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Message-ID: <CALUj-gvM+mupR6qhh=ruyFzY7VL8zGHpcJ9N0oLk4mT-UG_r6A@mail.gmail.com>
Date: Wed, 8 Apr 2020 21:46:15 +0530
From: rishi gupta <gupt21@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>, robh+dt@...nel.org
Cc: jslaby@...e.com, linux-serial@...r.kernel.org,
lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] tty/serial: ttvys: add null modem driver for emulation
Humble ping for feedback please!
Regards,
Rishi
On Sat, Feb 15, 2020 at 11:21 PM Rishi Gupta <gupt21@...il.com> wrote:
>
> The ttyvs driver creates virtual tty devices that can be
> used with standard POSIX APIs for serial port based applications.
> The driver is used mainly for testing user space applications.
>
> Devices can be created through device tree and through configfs.
> Various serial port events are emulated through a sysfs file.
>
> Signed-off-by: Rishi Gupta <gupt21@...il.com>
> ---
> Changes in v2:
> - Used configFS instead of misc subsystem
> - Added 'depends on CONFIGFS_FS' in Kconfig
> - Used IDR instead of associative array
> - Used tty_register_device_attr() to create sysfs with race with user-space
> - Used u16 wherever applicable instead of ushort
> - Use small x while defining hexadecimal numbers
> - Merged faulty cable sysfs into event sysfs node itself
> - Removed #define <linux/kernel.h>
> - Added #define <linux/uaccess.h>
> - Removed initial loopback & null-modem module parameters
> - Removed variables for device accounting (not needed due to configfs)
> - Used ATTRIBUTE_GROUPS macro
>
> MAINTAINERS | 8 +
> drivers/tty/Kconfig | 17 +
> drivers/tty/Makefile | 1 +
> drivers/tty/ttyvs.c | 2010 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 2036 insertions(+)
> create mode 100644 drivers/tty/ttyvs.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a0d8649..dedccfd 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -16973,6 +16973,14 @@ F: include/uapi/linux/serial_core.h
> F: include/uapi/linux/serial.h
> F: include/uapi/linux/tty.h
>
> +TTYVS VIRTUAL SERIAL DRIVER
> +M: Rishi Gupta <gupt21@...il.com>
> +L: linux-serial@...r.kernel.org
> +L: linux-kernel@...r.kernel.org
> +S: Maintained
> +F: Documentation/devicetree/bindings/serial/ttyvs.yaml
> +F: drivers/tty/ttyvs.c
> +
> TUA9001 MEDIA DRIVER
> M: Antti Palosaari <crope@....fi>
> L: linux-media@...r.kernel.org
> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> index a312cb3..3acb6d6 100644
> --- a/drivers/tty/Kconfig
> +++ b/drivers/tty/Kconfig
> @@ -477,4 +477,21 @@ config LDISC_AUTOLOAD
> dev.tty.ldisc_autoload sysctl, this configuration option will
> only set the default value of this functionality.
>
> +config TTY_VS
> + tristate "Virtual serial null modem emulation"
> + depends on CONFIGFS_FS
> + help
> + This driver creates virtual serial port devices (loopback and
> + null modem style) that can be used in the same way as real serial
> + port devices. Parity, frame, overflow, ring indicator, baudrate
> + mismatch, hardware and software flow control can be emulated.
> +
> + For information about how to create/delete devices, exchange data
> + and emulate events, please read:
> + <file:Documentation/devicetree/bindings/serial/ttyvs.yaml>.
> +
> + To compile this driver as a module, choose M here: the
> + module will be called ttyvs.ko. If you want to compile this driver
> + into the kernel, say Y here.
> +
> endif # TTY
> diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
> index 020b1cd..9d727ac 100644
> --- a/drivers/tty/Makefile
> +++ b/drivers/tty/Makefile
> @@ -33,6 +33,7 @@ obj-$(CONFIG_SYNCLINK) += synclink.o
> obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o
> obj-$(CONFIG_GOLDFISH_TTY) += goldfish.o
> obj-$(CONFIG_MIPS_EJTAG_FDC_TTY) += mips_ejtag_fdc.o
> +obj-$(CONFIG_TTY_VS) += ttyvs.o
> obj-$(CONFIG_VCC) += vcc.o
>
> obj-y += ipwireless/
> diff --git a/drivers/tty/ttyvs.c b/drivers/tty/ttyvs.c
> new file mode 100644
> index 0000000..3104900
> --- /dev/null
> +++ b/drivers/tty/ttyvs.c
> @@ -0,0 +1,2010 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Serial port null modem emulation driver
> + *
> + * Copyright (c) 2020, Rishi Gupta <gupt21@...il.com>
> + */
> +
> +/*
> + * Virtual multi-port serial card:
> + *
> + * This driver implements a virtual multi-port serial card in such a
> + * way that the card can have 0 to N number of virtual serial ports
> + * (tty devices). These devices can be used using standard termios
> + * and Linux/Posix APIs.
> + *
> + * DT bindings: Documentation/devicetree/bindings/serial/ttyvs.yaml
> + * Usage: Documentation/virtual/tty-ttyvs.rst
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/errno.h>
> +#include <linux/init.h>
> +#include <linux/idr.h>
> +#include <linux/module.h>
> +#include <linux/moduleparam.h>
> +#include <linux/slab.h>
> +#include <linux/wait.h>
> +#include <linux/tty.h>
> +#include <linux/tty_driver.h>
> +#include <linux/tty_flip.h>
> +#include <linux/serial.h>
> +#include <linux/sched.h>
> +#include <linux/version.h>
> +#include <linux/mutex.h>
> +#include <linux/device.h>
> +#include <linux/uaccess.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/configfs.h>
> +
> +/* Pin out configurations definitions */
> +#define VS_CON_CTS 0x0001
> +#define VS_CON_DCD 0x0002
> +#define VS_CON_DSR 0x0004
> +#define VS_CON_RI 0x0008
> +
> +/* Modem control register definitions */
> +#define VS_MCR_DTR 0x0001
> +#define VS_MCR_RTS 0x0002
> +#define VS_MCR_LOOP 0x0004
> +
> +/* Modem status register definitions */
> +#define VS_MSR_CTS 0x0008
> +#define VS_MSR_DCD 0x0010
> +#define VS_MSR_RI 0x0020
> +#define VS_MSR_DSR 0x0040
> +
> +/* UART frame structure definitions */
> +#define VS_CRTSCTS 0x0001
> +#define VS_XON 0x0002
> +#define VS_NONE 0x0004
> +#define VS_DATA_5 0x0008
> +#define VS_DATA_6 0x0010
> +#define VS_DATA_7 0x0020
> +#define VS_DATA_8 0x0040
> +#define VS_PARITY_NONE 0x0080
> +#define VS_PARITY_ODD 0x0100
> +#define VS_PARITY_EVEN 0x0200
> +#define VS_PARITY_MARK 0x0400
> +#define VS_PARITY_SPACE 0x0800
> +#define VS_STOP_1 0x1000
> +#define VS_STOP_2 0x2000
> +
> +/* Constants for the device type (odevtyp) */
> +#define VS_SNM 0x0001
> +#define VS_CNM 0x0002
> +#define VS_SLB 0x0003
> +#define VS_CLB 0x0004
> +
> +/* Attributes associated with a configfs item (folder/device) */
> +struct vs_cfs_dev_info {
> + struct config_group grp;
> + char *devtype;
> + int ownidx;
> + int peeridx;
> + u8 ortsmap;
> + u8 odtrmap;
> + u8 odtratopn;
> + u8 prtsmap;
> + u8 pdtrmap;
> + u8 pdtratopn;
> +};
> +
> +/* Represents a virtual tty device in this virtual card */
> +struct vs_dev {
> + /* index for this device in tty core */
> + unsigned int own_index;
> + /* index of the device to which this device is connected */
> + unsigned int peer_index;
> + /* shadow modem status register */
> + int msr_reg;
> + /* shadow modem control register */
> + int mcr_reg;
> + /* rts line connections for this device */
> + int rts_mappings;
> + /* dtr line connections for this device */
> + int dtr_mappings;
> + int set_odtr_at_open;
> + int set_pdtr_at_open;
> + int odevtyp;
> + /* mutual exclusion at device level */
> + struct mutex lock;
> + int is_break_on;
> + /* currently active baudrate */
> + int baud;
> + int uart_frame;
> + int waiting_msr_chg;
> + int tx_paused;
> + int faulty_cable;
> + struct tty_struct *own_tty;
> + struct tty_struct *peer_tty;
> + struct serial_struct serial;
> + struct async_icount icount;
> + struct device *device;
> +};
> +
> +/*
> + * Index radix tree based database of all devices managed by
> + * this driver.
> + */
> +static DEFINE_IDR(db);
> +
> +/* Used to create and destroy devices atomically/serially */
> +static DEFINE_MUTEX(card_lock);
> +
> +/* Describes this driver */
> +static struct tty_driver *ttyvs_driver;
> +
> +/* Maximum number of devices supported by this driver */
> +static ushort max_num_vs_devs = 64;
> +
> +/*
> + * Notifies tty core that a framing/parity/overrun error has happend
> + * while receiving data on serial port. When frame or parity error
> + * happens, -7/-8 (randomly selected number by this driver) is sent as
> + * byte that got corrupted to tty core. For emulation purpose 0 can
> + * not be taken as corrupted byte because parity and break both will
> + * have same sequence (octal \377 \0 \0) and therefore application
> + * will not be able to differentiate between these two.
> + *
> + * This is also used for asserting/de-asserting ring event on line and
> + * notifies tty core when a break condition has been detected on line.
> + *
> + * 1. Emulate framing error:
> + * $ echo "1" > /sys/class/tty/ttyvsN/event
> + *
> + * 2. Emulate parity error:
> + * $ echo "2" > /sys/class/tty/ttyvsN/event
> + *
> + * 3. Emulate overrun error:
> + * $ echo "3" > /sys/class/tty/ttyvsN/event
> + *
> + * 4. Emulate ring indicator (set RI signal):
> + * $ echo "4" > /sys/class/tty/ttyvsN/event
> + *
> + * 5. Emulate ring indicator (unset RI signal):
> + * $ echo "5" > /sys/class/tty/ttyvsN/event
> + *
> + * 6. Emulate break received:
> + * $ echo "6" > /sys/class/tty/ttyvsN/event
> + *
> + * 7. Emulate cable is faulty (data sent but not received):
> + * $ echo "7" > /sys/class/tty/ttyvsN/event
> + *
> + * 8. Remove faulty cable condition:
> + * $ echo "8" > /sys/class/tty/ttyvsN/event
> + */
> +static ssize_t event_store(struct device *dev,
> + struct device_attribute *attr, const char *buf, size_t count)
> +{
> + int ret, push = 1;
> + struct vs_dev *local_vsdev = dev_get_drvdata(dev);
> + struct tty_struct *tty_to_write = local_vsdev->own_tty;
> +
> + if (!buf || (count <= 0))
> + return -EINVAL;
> +
> + /*
> + * Ensure required structure has been allocated, initialized and
> + * port has been opened.
> + */
> + if (!tty_to_write || (tty_to_write->port == NULL)
> + || (tty_to_write->port->count <= 0))
> + return -EIO;
> + if (!test_bit(ASYNCB_INITIALIZED, &tty_to_write->port->flags))
> + return -EIO;
> +
> + mutex_lock(&local_vsdev->lock);
> +
> + switch (buf[0]) {
> + case '1':
> + ret = tty_insert_flip_char(tty_to_write->port, -7, TTY_FRAME);
> + if (ret < 0)
> + goto fail;
> + local_vsdev->icount.frame++;
> + break;
> + case '2':
> + ret = tty_insert_flip_char(tty_to_write->port, -8, TTY_PARITY);
> + if (ret < 0)
> + goto fail;
> + local_vsdev->icount.parity++;
> + break;
> + case '3':
> + ret = tty_insert_flip_char(tty_to_write->port, 0, TTY_OVERRUN);
> + if (ret < 0)
> + goto fail;
> + local_vsdev->icount.overrun++;
> + break;
> + case '4':
> + local_vsdev->msr_reg |= VS_MSR_RI;
> + local_vsdev->icount.rng++;
> + push = -1;
> + break;
> + case '5':
> + local_vsdev->msr_reg &= ~VS_MSR_RI;
> + local_vsdev->icount.rng++;
> + push = -1;
> + break;
> + case '6':
> + ret = tty_insert_flip_char(tty_to_write->port, 0, TTY_BREAK);
> + if (ret < 0)
> + goto fail;
> + local_vsdev->icount.brk++;
> + break;
> + case '7':
> + local_vsdev->faulty_cable = 1;
> + push = -1;
> + break;
> + case '8':
> + local_vsdev->faulty_cable = 0;
> + push = -1;
> + break;
> + default:
> + mutex_unlock(&local_vsdev->lock);
> + return -EINVAL;
> + }
> +
> + if (push)
> + tty_flip_buffer_push(tty_to_write->port);
> + ret = count;
> +
> +fail:
> + mutex_unlock(&local_vsdev->lock);
> + return ret;
> +}
> +static DEVICE_ATTR_WO(event);
> +
> +static struct attribute *ttyvs_attrs[] = {
> + &dev_attr_event.attr,
> + NULL,
> +};
> +ATTRIBUTE_GROUPS(ttyvs);
> +
> +/*
> + * Checks if the given serial port has received its carrier detect
> + * line raised or not. Return 1 if the carrier is raised otherwise 0.
> + */
> +static int vs_port_carrier_raised(struct tty_port *port)
> +{
> + struct vs_dev *local_vsdev = idr_find(&db, port->tty->index);
> +
> + return (local_vsdev->msr_reg & VS_MSR_DCD) ? 1 : 0;
> +}
> +
> +/* Shutdown the given serial port */
> +static void vs_port_shutdown(struct tty_port *port)
> +{
> + pr_debug("shutting down the port!\n");
> +}
> +
> +/*
> + * Invoked when tty is going to be destroyed and driver should
> + * release resources.
> + */
> +static void vs_port_destruct(struct tty_port *port)
> +{
> + pr_debug("destroying the port!\n");
> +}
> +
> +/* Activate the given serial port as opposed to shutdown */
> +static int vs_port_activate(struct tty_port *port, struct tty_struct *tty)
> +{
> + return 0;
> +}
> +
> +static const struct tty_port_operations vs_port_ops = {
> + .carrier_raised = vs_port_carrier_raised,
> + .shutdown = vs_port_shutdown,
> + .activate = vs_port_activate,
> + .destruct = vs_port_destruct,
> +};
> +
> +/*
> + * Update modem control and status registers according to the bit
> + * mask(s) provided. The RTS and DTR values can be set only if the
> + * current handshaking state of the tty device allows direct control
> + * of the modem control lines. The pin mappings are honoured.
> + *
> + * Caller holds lock of thegiven virtual tty device.
> + */
> +static int vs_update_modem_lines(struct tty_struct *tty,
> + unsigned int set, unsigned int clear)
> +{
> + int ctsint = 0;
> + int dcdint = 0;
> + int dsrint = 0;
> + int rngint = 0;
> + int mcr_ctrl_reg = 0;
> + int wakeup_blocked_open = 0;
> + int rts_mappings, dtr_mappings, msr_state_reg;
> + struct async_icount *evicount;
> + struct vs_dev *vsdev, *local_vsdev, *remote_vsdev;
> +
> + local_vsdev = idr_find(&db, tty->index);
> +
> + /* Read modify write MSR register */
> + if (tty->index != local_vsdev->peer_index) {
> + remote_vsdev = idr_find(&db, local_vsdev->peer_index);
> + msr_state_reg = remote_vsdev->msr_reg;
> + vsdev = remote_vsdev;
> + } else {
> + msr_state_reg = local_vsdev->msr_reg;
> + vsdev = local_vsdev;
> + }
> +
> + rts_mappings = local_vsdev->rts_mappings;
> + dtr_mappings = local_vsdev->dtr_mappings;
> +
> + if (set & TIOCM_RTS) {
> + mcr_ctrl_reg |= VS_MCR_RTS;
> + if ((rts_mappings & VS_CON_CTS) == VS_CON_CTS) {
> + msr_state_reg |= VS_MSR_CTS;
> + ctsint++;
> + }
> + if ((rts_mappings & VS_CON_DCD) == VS_CON_DCD) {
> + msr_state_reg |= VS_MSR_DCD;
> + dcdint++;
> + wakeup_blocked_open = 1;
> + }
> + if ((rts_mappings & VS_CON_DSR) == VS_CON_DSR) {
> + msr_state_reg |= VS_MSR_DSR;
> + dsrint++;
> + }
> + if ((rts_mappings & VS_CON_RI) == VS_CON_RI) {
> + msr_state_reg |= VS_MSR_RI;
> + rngint++;
> + }
> + }
> +
> + if (set & TIOCM_DTR) {
> + mcr_ctrl_reg |= VS_MCR_DTR;
> + if ((dtr_mappings & VS_CON_CTS) == VS_CON_CTS) {
> + msr_state_reg |= VS_MSR_CTS;
> + ctsint++;
> + }
> + if ((dtr_mappings & VS_CON_DCD) == VS_CON_DCD) {
> + msr_state_reg |= VS_MSR_DCD;
> + dcdint++;
> + wakeup_blocked_open = 1;
> + }
> + if ((dtr_mappings & VS_CON_DSR) == VS_CON_DSR) {
> + msr_state_reg |= VS_MSR_DSR;
> + dsrint++;
> + }
> + if ((dtr_mappings & VS_CON_RI) == VS_CON_RI) {
> + msr_state_reg |= VS_MSR_RI;
> + rngint++;
> + }
> + }
> +
> + if (clear & TIOCM_RTS) {
> + mcr_ctrl_reg &= ~VS_MCR_RTS;
> + if ((rts_mappings & VS_CON_CTS) == VS_CON_CTS) {
> + msr_state_reg &= ~VS_MSR_CTS;
> + ctsint++;
> + }
> + if ((rts_mappings & VS_CON_DCD) == VS_CON_DCD) {
> + msr_state_reg &= ~VS_MSR_DCD;
> + dcdint++;
> + }
> + if ((rts_mappings & VS_CON_DSR) == VS_CON_DSR) {
> + msr_state_reg &= ~VS_MSR_DSR;
> + dsrint++;
> + }
> + if ((rts_mappings & VS_CON_RI) == VS_CON_RI) {
> + msr_state_reg &= ~VS_MSR_RI;
> + rngint++;
> + }
> + }
> +
> + if (clear & TIOCM_DTR) {
> + mcr_ctrl_reg &= ~VS_MCR_DTR;
> + if ((dtr_mappings & VS_CON_CTS) == VS_CON_CTS) {
> + msr_state_reg &= ~VS_MSR_CTS;
> + ctsint++;
> + }
> + if ((dtr_mappings & VS_CON_DCD) == VS_CON_DCD) {
> + msr_state_reg &= ~VS_MSR_DCD;
> + dcdint++;
> + }
> + if ((dtr_mappings & VS_CON_DSR) == VS_CON_DSR) {
> + msr_state_reg &= ~VS_MSR_DSR;
> + dsrint++;
> + }
> + if ((dtr_mappings & VS_CON_RI) == VS_CON_RI) {
> + msr_state_reg &= ~VS_MSR_RI;
> + rngint++;
> + }
> + }
> +
> + local_vsdev->mcr_reg = mcr_ctrl_reg;
> + vsdev->msr_reg = msr_state_reg;
> +
> + evicount = &vsdev->icount;
> + evicount->cts += ctsint;
> + evicount->dsr += dsrint;
> + evicount->dcd += dcdint;
> + evicount->rng += rngint;
> +
> + if (vsdev->own_tty && vsdev->own_tty->port) {
> + /* Wake up process blocked on TIOCMIWAIT ioctl */
> + if ((vsdev->waiting_msr_chg == 1) &&
> + (vsdev->own_tty->port->count > 0)) {
> + wake_up_interruptible(
> + &vsdev->own_tty->port->delta_msr_wait);
> + }
> +
> + /* Wake up application blocked on carrier detect signal */
> + if ((wakeup_blocked_open == 1) &&
> + (vsdev->own_tty->port->blocked_open > 0)) {
> + wake_up_interruptible(&vsdev->own_tty->port->open_wait);
> + }
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Invoked when user space process opens a serial port. The tty core
> + * calls this to install tty and initialize the required resources.
> + */
> +static int vs_install(struct tty_driver *drv, struct tty_struct *tty)
> +{
> + int ret;
> + struct tty_port *port;
> +
> + port = kcalloc(1, sizeof(struct tty_port), GFP_KERNEL);
> + if (!port)
> + return -ENOMEM;
> +
> + /* First initialize and then set port operations */
> + tty_port_init(port);
> + port->ops = &vs_port_ops;
> +
> + ret = tty_port_install(port, drv, tty);
> + if (ret) {
> + kfree(port);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Invoked when there exist no user process or tty is to be
> + * released explicitly for whatever reason.
> + */
> +static void vs_cleanup(struct tty_struct *tty)
> +{
> + tty_port_put(tty->port);
> +}
> +
> +/*
> + * Called when open system call is called on virtual tty device node.
> + * The tty core allocates 'struct tty_struct' for this device and
> + * set up various resources, sets up line discipline and call this
> + * function. For first time allocation happens and from next time
> + * onwards only re-opening happens.
> + *
> + * The tty core finds the tty driver serving this device node and the
> + * index of this tty device as registered by this driver with tty core.
> + * From this inded we retrieve the virtual tty device to work on.
> + *
> + * If the same serial port is opened more than once, the tty structure
> + * passed to this function will be same but filp structure will be
> + * different every time. Caller holds tty lock.
> + *
> + * This driver does not set CLOCAL by default. This means that the
> + * open() system call will block until it find its carrier detect
> + * line raised. Application should use O_NONBLOCK/O_NDELAY flag if
> + * it does not want to wait for DCD line change.
> + */
> +static int vs_open(struct tty_struct *tty, struct file *filp)
> +{
> + int ret;
> + struct vs_dev *remote_vsdev;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + local_vsdev->own_tty = tty;
> +
> + /*
> + * If this device is one end of a null modem connection,
> + * provide its address to remote end.
> + */
> + if (tty->index != local_vsdev->peer_index) {
> + remote_vsdev = idr_find(&db, local_vsdev->peer_index);
> + remote_vsdev->peer_tty = tty;
> + }
> +
> + memset(&local_vsdev->serial, 0, sizeof(struct serial_struct));
> + memset(&local_vsdev->icount, 0, sizeof(struct async_icount));
> +
> + /*
> + * Handle DTR raising logic ourselve instead of tty_port helpers
> + * doing it. Locking virtual tty is not required here.
> + */
> + if (local_vsdev->set_odtr_at_open == 1)
> + vs_update_modem_lines(tty, TIOCM_DTR | TIOCM_RTS, 0);
> +
> + /* Associate tty with port and do port level opening. */
> + ret = tty_port_open(tty->port, tty, filp);
> + if (ret)
> + return ret;
> +
> + tty->port->close_delay = 0;
> + tty->port->closing_wait = ASYNC_CLOSING_WAIT_NONE;
> + tty->port->drain_delay = 0;
> +
> + return ret;
> +}
> +
> +/*
> + * Invoked by tty layer when release() is called on the file pointer
> + * that was previously created with a call to open().
> + */
> +static void vs_close(struct tty_struct *tty, struct file *filp)
> +{
> + if (test_bit(TTY_IO_ERROR, &tty->flags))
> + return;
> +
> + if (tty && filp && tty->port && (tty->port->count > 0))
> + tty_port_close(tty->port, tty, filp);
> +
> + if (tty && C_HUPCL(tty) && tty->port && (tty->port->count < 1))
> + vs_update_modem_lines(tty, 0, TIOCM_DTR | TIOCM_RTS);
> +}
> +
> +/*
> + * Invoked when write() system call is invoked on device node.
> + * This function constructs evry byte as per the current uart
> + * frame settings. Finally, the data is inserted into the tty
> + * buffer of the receiver tty device.
> + */
> +static int vs_write(struct tty_struct *tty,
> + const unsigned char *buf, int count)
> +{
> + int x;
> + unsigned char *data = NULL;
> + struct tty_struct *tty_to_write = NULL;
> + struct vs_dev *rx_vsdev = NULL;
> + struct vs_dev *tx_vsdev = idr_find(&db, tty->index);
> +
> + if (tx_vsdev->tx_paused || !tty || tty->stopped
> + || (count < 1) || !buf || tty->hw_stopped)
> + return 0;
> +
> + if (tx_vsdev->is_break_on == 1) {
> + pr_debug("break condition is on!\n");
> + return -EIO;
> + }
> +
> + if (tx_vsdev->faulty_cable == 1)
> + return count;
> +
> + if (tty->index != tx_vsdev->peer_index) {
> + /* Null modem */
> + tty_to_write = tx_vsdev->peer_tty;
> + rx_vsdev = idr_find(&db, tx_vsdev->peer_index);
> +
> + if ((tx_vsdev->baud != rx_vsdev->baud) ||
> + (tx_vsdev->uart_frame != rx_vsdev->uart_frame)) {
> + /*
> + * Emulate data sent but not received due to
> + * mismatched baudrate/framing.
> + */
> + pr_debug("mismatched serial port settings!\n");
> + tx_vsdev->icount.tx++;
> + return count;
> + }
> + } else {
> + /* Loop back */
> + tty_to_write = tty;
> + rx_vsdev = tx_vsdev;
> + }
> +
> + if (tty_to_write) {
> + if ((tty_to_write->termios.c_cflag & CSIZE) == CS8) {
> + data = (unsigned char *)buf;
> + } else {
> + data = kcalloc(count, sizeof(char), GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> +
> + /* Emulate correct number of data bits */
> + switch (tty_to_write->termios.c_cflag & CSIZE) {
> + case CS7:
> + for (x = 0; x < count; x++)
> + data[x] = buf[x] & 0x7F;
> + break;
> + case CS6:
> + for (x = 0; x < count; x++)
> + data[x] = buf[x] & 0x3F;
> + break;
> + case CS5:
> + for (x = 0; x < count; x++)
> + data[x] = buf[x] & 0x1F;
> + break;
> + default:
> + data = (unsigned char *)buf;
> + }
> + }
> +
> + tty_insert_flip_string(tty_to_write->port, data, count);
> + tty_flip_buffer_push(tty_to_write->port);
> + tx_vsdev->icount.tx++;
> + rx_vsdev->icount.rx++;
> +
> + if (data != buf)
> + kfree(data);
> + } else {
> + /*
> + * Other end is still not opened, emulate transmission from
> + * local end but don't make other end receive it as is the
> + * case in real world.
> + */
> + tx_vsdev->icount.tx++;
> + }
> +
> + return count;
> +}
> +
> +/* Invoked by tty core to transmit single data byte. */
> +static int vs_put_char(struct tty_struct *tty, unsigned char ch)
> +{
> + unsigned char data;
> + struct tty_struct *tty_to_write;
> + struct vs_dev *rx_vsdev;
> + struct vs_dev *tx_vsdev = idr_find(&db, tty->index);
> +
> + if (tx_vsdev->tx_paused || !tty || tty->stopped || tty->hw_stopped)
> + return 0;
> +
> + if (tx_vsdev->is_break_on == 1)
> + return -EIO;
> +
> + if (tx_vsdev->faulty_cable == 1)
> + return 1;
> +
> + if (tty->index != tx_vsdev->peer_index) {
> + tty_to_write = tx_vsdev->peer_tty;
> + rx_vsdev = idr_find(&db, tx_vsdev->peer_index);
> + if ((tx_vsdev->baud != rx_vsdev->baud) ||
> + (tx_vsdev->uart_frame != rx_vsdev->uart_frame)) {
> + tx_vsdev->icount.tx++;
> + return 1;
> + }
> + } else {
> + tty_to_write = tty;
> + rx_vsdev = tx_vsdev;
> + }
> +
> + if (tty_to_write != NULL) {
> + switch (tty_to_write->termios.c_cflag & CSIZE) {
> + case CS8:
> + data = ch;
> + break;
> + case CS7:
> + data = ch & 0x7F;
> + break;
> + case CS6:
> + data = ch & 0x3F;
> + break;
> + case CS5:
> + data = ch & 0x1F;
> + break;
> + default:
> + data = ch;
> + }
> + tty_insert_flip_string(tty_to_write->port, &data, 1);
> + tty_flip_buffer_push(tty_to_write->port);
> + tx_vsdev->icount.tx++;
> + rx_vsdev->icount.rx++;
> + } else {
> + tx_vsdev->icount.tx++;
> + }
> +
> + return 1;
> +}
> +
> +/*
> + * Flush the data out of serial port. This driver immediately
> + * pushes data into receiver's tty buffer hence do nothing here.
> + */
> +static void vs_flush_chars(struct tty_struct *tty)
> +{
> + pr_debug("flushing the chars!\n");
> +}
> +
> +/*
> + * Discard the internal output buffer for this tty device. Typically
> + * it may be called when executing IOCTL TCOFLUSH, closing the
> + * serial port, when break is received in input stream (flushing
> + * is configured) or when hangup occurs.
> + *
> + * On the other hand, when TCIFLUSH IOCTL is invoked, tty flip buffer
> + * and line discipline queue gets emptied without involvement of tty
> + * driver. The driver is generally expected not to keep data but send
> + * it to tty layer as soon as possible when it receives data.
> + *
> + * As this driver immediately pushes data into receiver's tty buffer
> + * hence do nothing here.
> + */
> +static void vs_flush_buffer(struct tty_struct *tty)
> +{
> + pr_debug("flushing the buffer!\n");
> +}
> +
> +/* Provides information as a repsonse to TIOCGSERIAL IOCTL */
> +static int vs_get_serinfo(struct tty_struct *tty, unsigned long arg)
> +{
> + int ret;
> + struct serial_struct info;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> + struct serial_struct serial = local_vsdev->serial;
> +
> + if (!arg)
> + return -EFAULT;
> +
> + memset(&info, 0, sizeof(info));
> +
> + info.type = PORT_UNKNOWN;
> + info.line = serial.line;
> + info.port = tty->index;
> + info.irq = 0;
> + info.flags = tty->port->flags;
> + info.xmit_fifo_size = 0;
> + info.baud_base = 0;
> + info.close_delay = tty->port->close_delay;
> + info.closing_wait = tty->port->closing_wait;
> + info.custom_divisor = 0;
> + info.hub6 = 0;
> + info.io_type = SERIAL_IO_MEM;
> +
> + ret = copy_to_user((void __user *)arg, &info,
> + sizeof(struct serial_struct));
> +
> + return ret ? -EFAULT : 0;
> +}
> +
> +/* Returns number of bytes that can be queued to this device now */
> +static int vs_write_room(struct tty_struct *tty)
> +{
> + struct vs_dev *tx_vsdev = idr_find(&db, tty->index);
> +
> + if (tx_vsdev->tx_paused || !tty ||
> + tty->stopped || tty->hw_stopped)
> + return 0;
> +
> + return 2048;
> +}
> +
> +/*
> + * Invoked when serial terminal settings are chaged. The old_termios
> + * contains currently active settings and tty->termios contains new
> + * settings to be applied.
> + */
> +static void vs_set_termios(struct tty_struct *tty,
> + struct ktermios *old_termios)
> +{
> + u32 baud;
> + int uart_frame_settings;
> + unsigned int mask = TIOCM_DTR;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> +
> + /*
> + * Typically B0 is used to terminate the connection.
> + * Drop RTS and DTR.
> + */
> + if ((tty->termios.c_cflag & CBAUD) == B0) {
> + vs_update_modem_lines(tty, 0, TIOCM_DTR | TIOCM_RTS);
> + mutex_unlock(&local_vsdev->lock);
> + return;
> + }
> +
> + /* If coming out of B0, raise DTR and RTS. This might get
> + * overridden in next steps. Applications like minicom when
> + * opens a serial port, may drop speed to B0 and then back
> + * to normal speed again.
> + */
> + if (!old_termios || (old_termios->c_cflag & CBAUD) == B0) {
> + if (!(tty->termios.c_cflag & CRTSCTS) ||
> + !test_bit(TTY_THROTTLED, &tty->flags)) {
> + mask |= TIOCM_RTS;
> + vs_update_modem_lines(tty, mask, 0);
> + }
> + }
> +
> + baud = tty_get_baud_rate(tty);
> + if (!baud)
> + baud = 9600;
> +
> + tty_encode_baud_rate(tty, baud, baud);
> +
> + local_vsdev->baud = baud;
> +
> + uart_frame_settings = 0;
> + if (tty->termios.c_cflag & CRTSCTS) {
> + uart_frame_settings |= VS_CRTSCTS;
> + } else if ((tty->termios.c_iflag & IXON) ||
> + (tty->termios.c_iflag & IXOFF)) {
> + uart_frame_settings |= VS_XON;
> + } else {
> + uart_frame_settings |= VS_NONE;
> + }
> +
> + switch (tty->termios.c_cflag & CSIZE) {
> + case CS8:
> + uart_frame_settings |= VS_DATA_8;
> + break;
> + case CS7:
> + uart_frame_settings |= VS_DATA_7;
> + break;
> + case CS6:
> + uart_frame_settings |= VS_DATA_6;
> + break;
> + case CS5:
> + uart_frame_settings |= VS_DATA_5;
> + break;
> + default:
> + uart_frame_settings |= VS_DATA_8;
> + }
> +
> + if (tty->termios.c_cflag & CSTOPB)
> + uart_frame_settings |= VS_STOP_2;
> + else
> + uart_frame_settings |= VS_STOP_1;
> +
> + if (tty->termios.c_cflag & PARENB) {
> + if (tty->termios.c_cflag & CMSPAR) {
> + if (tty->termios.c_cflag & PARODD)
> + uart_frame_settings |= VS_PARITY_MARK;
> + else
> + uart_frame_settings |= VS_PARITY_SPACE;
> + } else {
> + if (tty->termios.c_cflag & PARODD)
> + uart_frame_settings |= VS_PARITY_ODD;
> + else
> + uart_frame_settings |= VS_PARITY_EVEN;
> + }
> + } else {
> + uart_frame_settings |= VS_PARITY_NONE;
> + }
> +
> + local_vsdev->uart_frame = uart_frame_settings;
> +
> + mutex_unlock(&local_vsdev->lock);
> +}
> +
> +/*
> + * Returns the number of bytes in device's output queue. This is
> + * invoked when TIOCOUTQ IOCTL is executed or by tty core as and
> + * when required. Because we all push all data into receiver's
> + * end tty buffer, always return 0 here.
> + */
> +static int vs_chars_in_buffer(struct tty_struct *tty)
> +{
> + return 0;
> +}
> +
> +/*
> + * Based on the number od interrupts check if any of the signal
> + * line has changed.
> + */
> +static int vs_check_msr_delta(struct tty_struct *tty,
> + struct vs_dev *local_vsdev, unsigned long mask,
> + struct async_icount *prev)
> +{
> + int delta;
> + struct async_icount now;
> +
> + /*
> + * Use tty-port initialised flag to detect all hangups
> + * including the disconnect(device destroy) event.
> + */
> + if (!test_bit(ASYNCB_INITIALIZED, &tty->port->flags))
> + return 1;
> +
> + mutex_lock(&local_vsdev->lock);
> + now = local_vsdev->icount;
> + mutex_unlock(&local_vsdev->lock);
> + delta = ((mask & TIOCM_RNG && prev->rng != now.rng) ||
> + (mask & TIOCM_DSR && prev->dsr != now.dsr) ||
> + (mask & TIOCM_CAR && prev->dcd != now.dcd) ||
> + (mask & TIOCM_CTS && prev->cts != now.cts));
> +
> + *prev = now;
> + return delta;
> +}
> +
> +/* Sleeps until at-least one of the modem lines changes */
> +static int vs_wait_change(struct tty_struct *tty, unsigned long mask)
> +{
> + int ret;
> + struct async_icount prev;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> +
> + local_vsdev->waiting_msr_chg = 1;
> + prev = local_vsdev->icount;
> +
> + mutex_unlock(&local_vsdev->lock);
> +
> + ret = wait_event_interruptible(tty->port->delta_msr_wait,
> + vs_check_msr_delta(tty, local_vsdev, mask, &prev));
> +
> + local_vsdev->waiting_msr_chg = 0;
> +
> + if (!ret && !test_bit(ASYNCB_INITIALIZED, &tty->port->flags))
> + ret = -EIO;
> +
> + return ret;
> +}
> +
> +/* Execute IOCTL commands */
> +static int vs_ioctl(struct tty_struct *tty,
> + unsigned int cmd, unsigned long arg)
> +{
> + switch (cmd) {
> + case TIOCGSERIAL:
> + return vs_get_serinfo(tty, arg);
> + case TIOCMIWAIT:
> + return vs_wait_change(tty, arg);
> + }
> +
> + return -ENOIOCTLCMD;
> +}
> +
> +/*
> + * Invoked when tty layer's input buffers are about to get full.
> + *
> + * When using RTS/CTS flow control, when RTS line is de-asserted,
> + * interrupt will be generated in hardware. The interrupt handler
> + * will raise a flag to indicate transmission should be stopped.
> + * This is achieved in this driver through tx_paused variable.
> + */
> +static void vs_throttle(struct tty_struct *tty)
> +{
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> + struct vs_dev *remote_vsdev = idr_find(&db, local_vsdev->peer_index);
> +
> + if (tty->termios.c_cflag & CRTSCTS) {
> + mutex_lock(&local_vsdev->lock);
> + remote_vsdev->tx_paused = 1;
> + vs_update_modem_lines(tty, 0, TIOCM_RTS);
> + mutex_unlock(&local_vsdev->lock);
> + } else if ((tty->termios.c_iflag & IXON) ||
> + (tty->termios.c_iflag & IXOFF)) {
> + vs_put_char(tty, STOP_CHAR(tty));
> + } else {
> + /* do nothing */
> + }
> +}
> +
> +/*
> + * Invoked when the tty layer's input buffers have been emptied out,
> + * and it now can accept more data. Throttle/Unthrottle is about
> + * notifying remote end to start or stop data as per the currently
> + * active flow control. On the other hand, Start/Stop is about what
> + * action to take at local end itself to start or stop data as per
> + * the currently active flow control.
> + */
> +static void vs_unthrottle(struct tty_struct *tty)
> +{
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> + struct vs_dev *remote_vsdev = idr_find(&db, local_vsdev->peer_index);
> +
> + if (tty->termios.c_cflag & CRTSCTS) {
> + /* hardware (RTS/CTS) flow control */
> + mutex_lock(&local_vsdev->lock);
> + remote_vsdev->tx_paused = 0;
> + vs_update_modem_lines(tty, TIOCM_RTS, 0);
> + mutex_unlock(&local_vsdev->lock);
> +
> + if (remote_vsdev->own_tty && remote_vsdev->own_tty->port)
> + tty_port_tty_wakeup(remote_vsdev->own_tty->port);
> + } else if ((tty->termios.c_iflag & IXON) ||
> + (tty->termios.c_iflag & IXOFF)) {
> + /* software flow control */
> + vs_put_char(tty, START_CHAR(tty));
> + } else {
> + /* do nothing */
> + }
> +}
> +
> +/*
> + * Invoked when this driver should stop sending data for example
> + * as a part of flow control mechanism.
> + *
> + * Line discipline n_tty calls this function if this device uses
> + * software flow control and an XOFF character is received from
> + * other end.
> + */
> +static void vs_stop(struct tty_struct *tty)
> +{
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> + local_vsdev->tx_paused = 1;
> + mutex_unlock(&local_vsdev->lock);
> +}
> +
> +/*
> + * Invoked when this driver should start sending data for example
> + * as a part of flow control mechanism.
> + *
> + * Line discipline n_tty calls this function if this device uses
> + * software flow control and an XON character is received from
> + * other end.
> + */
> +static void vs_start(struct tty_struct *tty)
> +{
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> + local_vsdev->tx_paused = 0;
> + mutex_unlock(&local_vsdev->lock);
> +
> + if (tty && tty->port)
> + tty_port_tty_wakeup(tty->port);
> +}
> +
> +/*
> + * Obtain the modem status bits for the given tty device. Invoked
> + * typically when TIOCMGET IOCTL is executed on the given
> + * tty device.
> + */
> +static int vs_tiocmget(struct tty_struct *tty)
> +{
> + int status, msr_reg, mcr_reg;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> + mcr_reg = local_vsdev->mcr_reg;
> + msr_reg = local_vsdev->msr_reg;
> + mutex_unlock(&local_vsdev->lock);
> +
> + status = ((mcr_reg & VS_MCR_DTR) ? TIOCM_DTR : 0) |
> + ((mcr_reg & VS_MCR_RTS) ? TIOCM_RTS : 0) |
> + ((mcr_reg & VS_MCR_LOOP) ? TIOCM_LOOP : 0) |
> + ((msr_reg & VS_MSR_DCD) ? TIOCM_CAR : 0) |
> + ((msr_reg & VS_MSR_RI) ? TIOCM_RI : 0) |
> + ((msr_reg & VS_MSR_CTS) ? TIOCM_CTS : 0) |
> + ((msr_reg & VS_MSR_DSR) ? TIOCM_DSR : 0);
> +
> + return status;
> +}
> +
> +/*
> + * Set the modem status bits. Invoked typically when TIOCMSET IOCTL
> + * is executed on the given tty device.
> + */
> +static int vs_tiocmset(struct tty_struct *tty,
> + unsigned int set, unsigned int clear)
> +{
> + int ret;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> + ret = vs_update_modem_lines(tty, set, clear);
> + mutex_unlock(&local_vsdev->lock);
> +
> + return ret;
> +}
> +
> +/*
> + * Unconditionally assert/de-assert break condition of the given
> + * tty device.
> + */
> +static int vs_break_ctl(struct tty_struct *tty, int break_state)
> +{
> + struct tty_struct *tty_to_write;
> + struct vs_dev *brk_rx_vsdev;
> + struct vs_dev *brk_tx_vsdev = idr_find(&db, tty->index);
> +
> + if (tty->index != brk_tx_vsdev->peer_index) {
> + tty_to_write = brk_tx_vsdev->peer_tty;
> + brk_rx_vsdev = idr_find(&db, brk_tx_vsdev->peer_index);
> + } else {
> + tty_to_write = tty;
> + brk_rx_vsdev = brk_tx_vsdev;
> + }
> +
> + mutex_lock(&brk_tx_vsdev->lock);
> +
> + if (break_state != 0) {
> + if (brk_tx_vsdev->is_break_on == 1)
> + return 0;
> +
> + brk_tx_vsdev->is_break_on = 1;
> + if (tty_to_write != NULL) {
> + tty_insert_flip_char(tty_to_write->port, 0, TTY_BREAK);
> + tty_flip_buffer_push(tty_to_write->port);
> + brk_rx_vsdev->icount.brk++;
> + }
> + } else {
> + brk_tx_vsdev->is_break_on = 0;
> + }
> +
> + mutex_unlock(&brk_tx_vsdev->lock);
> + return 0;
> +}
> +
> +/*
> + * Invoked by tty layer to inform this driver that it should hangup
> + * the tty device (lower modem control lines after last process
> + * using tty devices closes the device or exited).
> + *
> + * Drop DTR/RTS if HUPCL is set. This causes any attached modem to
> + * hang up the line.
> + *
> + * On the receiving end, if CLOCAL bit is set, DCD will be ignored
> + * otherwise SIGHUP may be generated to indicate a line disconnect
> + * event.
> + */
> +static void vs_hangup(struct tty_struct *tty)
> +{
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> +
> + /* Drops reference to tty */
> + tty_port_hangup(tty->port);
> +
> + if (tty && C_HUPCL(tty))
> + vs_update_modem_lines(tty, 0, TIOCM_DTR | TIOCM_RTS);
> +
> + mutex_unlock(&local_vsdev->lock);
> + pr_debug("hanged up!\n");
> +}
> +
> +/*
> + * Return number of interrupts as response to TIOCGICOUNT IOCTL.
> + * Both 1->0 and 0->1 transitions are counted, except for RI;
> + * where only 0->1 transitions are accounted.
> + */
> +static int vs_get_icount(struct tty_struct *tty,
> + struct serial_icounter_struct *icount)
> +{
> + struct async_icount cnow;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + mutex_lock(&local_vsdev->lock);
> + cnow = local_vsdev->icount;
> + mutex_unlock(&local_vsdev->lock);
> +
> + icount->cts = cnow.cts;
> + icount->dsr = cnow.dsr;
> + icount->rng = cnow.rng;
> + icount->dcd = cnow.dcd;
> + icount->tx = cnow.tx;
> + icount->rx = cnow.rx;
> + icount->frame = cnow.frame;
> + icount->parity = cnow.parity;
> + icount->overrun = cnow.overrun;
> + icount->brk = cnow.brk;
> + icount->buf_overrun = cnow.buf_overrun;
> +
> + return 0;
> +}
> +
> +/*
> + * Invoked by tty layer to execute TCIOFF and TCION IOCTL commands
> + * generally because user space process called tcflow() function.
> + * It send a high priority character to the tty device end even if
> + * stopped.
> + *
> + * If this function (send_xchar) is defined by tty device driver,
> + * tty core will call this function. If it is not specified then
> + * tty core will first instruct this driver to start transmission
> + * (start()) and then invoke write() of this driver passing character
> + * to be written and then it will call stop() of this driver.
> + */
> +static void vs_send_xchar(struct tty_struct *tty, char ch)
> +{
> + int was_paused;
> + struct vs_dev *local_vsdev = idr_find(&db, tty->index);
> +
> + was_paused = local_vsdev->tx_paused;
> + if (was_paused)
> + local_vsdev->tx_paused = 0;
> +
> + vs_put_char(tty, ch);
> + if (was_paused)
> + local_vsdev->tx_paused = 1;
> +}
> +
> +/*
> + * Invoked by tty core in response to tcdrain() call. As this driver
> + * drains on write() itself, we return immediately from here.
> + */
> +static void vs_wait_until_sent(struct tty_struct *tty, int timeout)
> +{
> + pr_debug("returned wait until sent!\n");
> +}
> +
> +/*
> + * Unregister tty device specified by minor number ownidx
> + * and remove sysfs files associate with it. Caller must
> + * hold card lock. First tty must be released and then port.
> + *
> + * It is common to reset environment before launching new test
> + * suite during automated testing. To support this we allow
> + * removing devices even when it was created using DT as of
> + * now till we find any valid reason not do so.
> + */
> +static void vs_unreg_one_dev(int ownidx, struct vs_dev *vsdev)
> +{
> + struct tty_struct *tty;
> +
> + if (vsdev->own_tty && vsdev->own_tty->port) {
> + tty = tty_port_tty_get(vsdev->own_tty->port);
> + if (tty) {
> + tty_vhangup(tty);
> + tty_kref_put(tty);
> + }
> + }
> +
> + tty_unregister_device(ttyvs_driver, ownidx);
> +}
> +
> +/*
> + * Destroy a virtual tty device specified by the given index.
> + * Whether IDR id will be freed or not is specified by the
> + * caller through free_idr.
> + */
> +static int vs_del_specific_devs(int ownidx, int free_idr)
> +{
> + struct vs_dev *vsdev1, *vsdev2;
> +
> + /*
> + * If user just created configfs item but did not populated valid
> + * index, device will not exist, so bail out early.
> + */
> + vsdev1 = idr_find(&db, ownidx);
> + if (!vsdev1)
> + return 0;
> +
> + vs_unreg_one_dev(ownidx, vsdev1);
> +
> + /* If this device is part of a null modem, delete peer also */
> + if (vsdev1->own_index != vsdev1->peer_index) {
> + vsdev2 = idr_find(&db, vsdev1->peer_index);
> + if (vsdev2) {
> + vs_unreg_one_dev(vsdev2->own_index, vsdev2);
> + if (free_idr)
> + idr_remove(&db, vsdev2->own_index);
> + kfree(vsdev2);
> + }
> + }
> +
> + if (free_idr)
> + idr_remove(&db, ownidx);
> + kfree(vsdev1);
> +
> + return 0;
> +}
> +
> +/*
> + * Destroy all tty devices created, mark all the indexes as
> + * available for allocation; reset IDR for re-use.
> + */
> +static void vs_del_all_devs(void)
> +{
> + int x;
> + struct vs_dev *vsdev;
> +
> + mutex_lock(&card_lock);
> +
> + idr_for_each_entry(&db, vsdev, x)
> + vs_del_specific_devs(vsdev->own_index, 0);
> +
> + idr_destroy(&db);
> +
> + mutex_unlock(&card_lock);
> +}
> +
> +/*
> + * Allocate per device private data (vsdev) for this driver, register
> + * with tty core and create custom sysfs nodes for emulating serial
> + * port events. Caller should hold card lock.
> + */
> +static int vs_alloc_reg_one_dev(int oidx, int pidx, int rtsmap,
> + int dtrmap, int dtropn)
> +{
> + int ret, id;
> + struct vs_dev *vsdev;
> + struct device *dev;
> +
> + /* Allocate and init virtual tty device's private data */
> + vsdev = kcalloc(1, sizeof(struct vs_dev), GFP_KERNEL);
> + if (!vsdev)
> + return -ENOMEM;
> +
> + id = idr_alloc(&db, vsdev, oidx, oidx + 1, GFP_KERNEL);
> + if (id < 0) {
> + ret = id;
> + goto fail_id;
> + }
> +
> + vsdev->own_tty = NULL;
> + vsdev->peer_tty = NULL;
> + vsdev->own_index = oidx;
> + vsdev->peer_index = pidx;
> + vsdev->rts_mappings = rtsmap;
> + vsdev->dtr_mappings = dtrmap;
> + vsdev->set_odtr_at_open = dtropn;
> + vsdev->msr_reg = 0;
> + vsdev->mcr_reg = 0;
> + vsdev->waiting_msr_chg = 0;
> + vsdev->tx_paused = 0;
> + vsdev->faulty_cable = 0;
> + mutex_init(&vsdev->lock);
> +
> + /*
> + * Register with tty core with a specific minor number.
> + * Driver core itself will create sysfs nodes (ttyvs_groups).
> + */
> + dev = tty_register_device_attr(ttyvs_driver, oidx, NULL,
> + vsdev, ttyvs_groups);
> + if (!dev) {
> + ret = -ENOMEM;
> + goto fail_reg;
> + }
> +
> + vsdev->device = dev;
> + return 0;
> +
> +fail_reg:
> + idr_remove(&db, id);
> +fail_id:
> + kfree(vsdev);
> + return ret;
> +}
> +
> +/*
> + * Extract pin mappings from local to remote tty devices.
> + * The map contains bits setted by user. Returns 0 on success
> + * or negative error code on error. The *mapping will contain
> + * pin connections (bit map as used by this driver) when this
> + * function returns.
> + */
> +static int vs_extract_pin_mapping(int usrval, int *mapping)
> +{
> + if (usrval > (VS_CON_CTS | VS_CON_DCD | VS_CON_DSR | VS_CON_RI))
> + return -EINVAL;
> +
> + /* No pin connections by-default */
> + *mapping = 0;
> +
> + if ((usrval & VS_CON_CTS) == VS_CON_CTS)
> + *mapping |= VS_CON_CTS;
> +
> + if ((usrval & VS_CON_DCD) == VS_CON_DCD)
> + *mapping |= VS_CON_DCD;
> +
> + if ((usrval & VS_CON_DSR) == VS_CON_DSR)
> + *mapping |= VS_CON_DSR;
> +
> + if ((usrval & VS_CON_RI) == VS_CON_RI)
> + *mapping |= VS_CON_RI;
> +
> + return 0;
> +}
> +
> +/*
> + * The devtyp is 1 for null modem and 0 for loop-back. We extract
> + * user supplied information, validate it and convert it as
> + * required by this driver to create a device.
> + */
> +static int vs_extract_dev_param_cfs(const struct vs_cfs_dev_info *di,
> + unsigned int *idx, int *rtsmap, int *dtrmap,
> + int *dtratopen, int devtyp)
> +{
> + int ret;
> +
> + if (devtyp) {
> + if (di->peeridx >= max_num_vs_devs)
> + return -EINVAL;
> +
> + *idx = di->peeridx;
> +
> + ret = vs_extract_pin_mapping(di->prtsmap, rtsmap);
> + if (ret)
> + return ret;
> +
> + ret = vs_extract_pin_mapping(di->pdtrmap, rtsmap);
> + if (ret)
> + return ret;
> +
> + *dtratopen = di->pdtratopn ? 1 : 0;
> + } else {
> + if (di->ownidx >= max_num_vs_devs)
> + return -EINVAL;
> +
> + *idx = di->ownidx;
> +
> + ret = vs_extract_pin_mapping(di->ortsmap, rtsmap);
> + if (ret)
> + return ret;
> +
> + ret = vs_extract_pin_mapping(di->odtrmap, rtsmap);
> + if (ret)
> + return ret;
> +
> + *dtratopen = di->odtratopn ? 1 : 0;
> + }
> +
> + return 0;
> +}
> +
> +/* Converts pin mappings from dt node to this driver specific bit map */
> +static int vs_parse_dt_get_map(const struct device_node *np,
> + const char *prop, int *mapping)
> +{
> + int x, ret, num_map;
> + int val[4];
> +
> + /*
> + * If the RTS/DTR pin is unconnected (property doesn't exist)
> + * set mapping to 0 and return success.
> + */
> + ret = of_property_count_u32_elems(np, prop);
> + if (ret < 0) {
> + if (ret == -EINVAL) {
> + *mapping = 0;
> + return 0;
> + }
> + return ret;
> + }
> +
> + /*
> + * A given pin can be connected to 1,6,8,9 pins. Therefore if
> + * more then 4 mappings are defined in DT, ignore it.
> + */
> + num_map = ret;
> + if (ret > 4)
> + num_map = 4;
> +
> + ret = of_property_read_u32_array(np, prop, val, num_map);
> + if (ret < 0)
> + return ret;
> +
> + *mapping = 0;
> + for (x = 0; x < num_map; x++) {
> + switch (val[x]) {
> + case 8:
> + *mapping |= VS_CON_CTS;
> + break;
> + case 1:
> + *mapping |= VS_CON_DCD;
> + break;
> + case 6:
> + *mapping |= VS_CON_DSR;
> + break;
> + case 9:
> + *mapping |= VS_CON_RI;
> + break;
> + default:
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Extract index of device, RTS mappings, DTR mappings and
> + * whether to assert DTR at device open or not from dt node.
> + */
> +static int vs_extract_dev_param_dt(const struct device_node *np,
> + unsigned int *idx, int *rtsmap, int *dtrmap,
> + int *dtratopen, int exclude)
> +{
> + int ret;
> +
> + ret = of_property_read_u32(np, "dev-num", idx);
> + if (ret)
> + return ret;
> +
> + if (*idx >= max_num_vs_devs)
> + return -EINVAL;
> +
> + ret = vs_parse_dt_get_map(np, "rtsmap", rtsmap);
> + if (ret)
> + return ret;
> +
> + ret = vs_parse_dt_get_map(np, "dtrmap", dtrmap);
> + if (ret)
> + return ret;
> +
> + *dtratopen = of_property_read_bool(np,
> + "set-dtr-at-open") ? 1 : 0;
> +
> + return 0;
> +}
> +
> +/*
> + * Create a loop-back style device:
> + *
> + * 0. Information about device parameters can come through either
> + * configfs node or device-tree node.
> + * 1. Decide index to use; the number is specified by user. If the
> + * given index is used already through error.
> + * 2. Extract RTS and DTR mappings. A pin can map to pin numbers
> + * 1,6,8,9 only or might be un-connected. Through error if
> + * invalid mapping is given.
> + * 3. Find if DTR should be asserted when tty device is opened or
> + * not.
> + * 4. Allocate and initialize 'struct vs_dev' instance with info
> + * from steps 1,2 & 3.
> + * 5. Register one tty device with tty core and associate this tty
> + * device with vsdev instance from step 4.
> + * 6. Create custom sysfs nodes to emulate serial port events for
> + * this device.
> + */
> +static int vs_add_lb(const struct vs_cfs_dev_info *di,
> + const struct device_node *np)
> +{
> + int ret, rtsmap, dtrmap, dtratopen;
> + unsigned int idx;
> +
> + mutex_lock(&card_lock);
> +
> + if (di) {
> + ret = vs_extract_dev_param_cfs(di, &idx, &rtsmap,
> + &dtrmap, &dtratopen, 0);
> + } else {
> + ret = vs_extract_dev_param_dt(np, &idx, &rtsmap,
> + &dtrmap, &dtratopen, -1);
> + }
> + if (ret)
> + goto fail;
> +
> + ret = vs_alloc_reg_one_dev(idx, idx, rtsmap, dtrmap, dtratopen);
> + if (ret)
> + goto fail;
> +
> +fail:
> + mutex_unlock(&card_lock);
> + return ret;
> +}
> +
> +/*
> + * Create a null-modem style pair of devices:
> + *
> + * Steps are same as for creating loop-back style device except,
> + * we create both the devices on success or none of them on error.
> + */
> +static int vs_add_nm(const struct vs_cfs_dev_info *di,
> + const struct device_node *np1,
> + const struct device_node *np2)
> +{
> + int ret, rtsmap1, dtrmap1, dtratopen1;
> + int rtsmap2, dtrmap2, dtratopen2;
> + unsigned int idx1, idx2;
> +
> + mutex_lock(&card_lock);
> +
> + if (di) {
> + ret = vs_extract_dev_param_cfs(di, &idx1, &rtsmap1, &dtrmap1,
> + &dtratopen1, 0);
> + if (ret)
> + goto out;
> +
> + ret = vs_extract_dev_param_cfs(di, &idx2, &rtsmap2, &dtrmap2,
> + &dtratopen2, 1);
> + } else {
> + ret = vs_extract_dev_param_dt(np1, &idx1, &rtsmap1,
> + &dtrmap1, &dtratopen1, -1);
> + if (ret)
> + goto out;
> +
> + ret = vs_extract_dev_param_dt(np2, &idx2, &rtsmap2,
> + &dtrmap2, &dtratopen2, idx1);
> + }
> + if (ret)
> + goto out;
> +
> + ret = vs_alloc_reg_one_dev(idx1, idx2, rtsmap1, dtrmap1, dtratopen1);
> + if (ret)
> + goto out;
> +
> + ret = vs_alloc_reg_one_dev(idx2, idx1, rtsmap2, dtrmap2, dtratopen2);
> + if (ret)
> + vs_del_specific_devs(idx1, 1);
> +
> +out:
> + mutex_unlock(&card_lock);
> + return ret;
> +}
> +
> +static const struct tty_operations vs_serial_ops = {
> + .install = vs_install,
> + .cleanup = vs_cleanup,
> + .open = vs_open,
> + .close = vs_close,
> + .write = vs_write,
> + .put_char = vs_put_char,
> + .flush_chars = vs_flush_chars,
> + .write_room = vs_write_room,
> + .chars_in_buffer = vs_chars_in_buffer,
> + .ioctl = vs_ioctl,
> + .set_termios = vs_set_termios,
> + .throttle = vs_throttle,
> + .unthrottle = vs_unthrottle,
> + .stop = vs_stop,
> + .start = vs_start,
> + .hangup = vs_hangup,
> + .break_ctl = vs_break_ctl,
> + .flush_buffer = vs_flush_buffer,
> + .wait_until_sent = vs_wait_until_sent,
> + .send_xchar = vs_send_xchar,
> + .tiocmget = vs_tiocmget,
> + .tiocmset = vs_tiocmset,
> + .get_icount = vs_get_icount,
> +};
> +
> +static int vs_register_with_tty_core(void)
> +{
> + int ret;
> +
> + /* Initialize and register this driver with tty core */
> + ttyvs_driver = tty_alloc_driver(max_num_vs_devs, 0);
> + if (IS_ERR(ttyvs_driver))
> + return PTR_ERR(ttyvs_driver);
> +
> + ttyvs_driver->owner = THIS_MODULE;
> + ttyvs_driver->driver_name = "ttyvs";
> + ttyvs_driver->name = "ttyvs";
> + ttyvs_driver->major = 0;
> + ttyvs_driver->minor_start = 0;
> + ttyvs_driver->type = TTY_DRIVER_TYPE_SERIAL;
> + ttyvs_driver->subtype = SERIAL_TYPE_NORMAL;
> + ttyvs_driver->flags = TTY_DRIVER_REAL_RAW
> + | TTY_DRIVER_RESET_TERMIOS
> + | TTY_DRIVER_DYNAMIC_DEV;
> + ttyvs_driver->init_termios = tty_std_termios;
> + ttyvs_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL;
> + ttyvs_driver->init_termios.c_ispeed = 9600;
> + ttyvs_driver->init_termios.c_ospeed = 9600;
> +
> + tty_set_operations(ttyvs_driver, &vs_serial_ops);
> +
> + ret = tty_register_driver(ttyvs_driver);
> + if (ret)
> + put_tty_driver(ttyvs_driver);
> +
> + return ret;
> +}
> +
> +/*
> + * Information passed through device tree is given more preference
> + * then through module params. This parses all device nodes and
> + * creates loop-back and null-modem ttyvsX devices in the process.
> + */
> +static int ttyvs_device_probe(struct platform_device *pdev)
> +{
> + int ret;
> + u32 max_num;
> + struct device_node *child, *peer_node;
> + phandle peer;
> + struct device *dev = &pdev->dev;
> + struct device_node *np = dev->of_node;
> +
> + /*
> + * We register with tty core again only if maximum number of
> + * devices registered during module_init is changed by device
> + * tree.
> + */
> + max_num = 0;
> + ret = of_property_read_u32(np, "max-num-vs-devs", &max_num);
> + if (!ret && (max_num != max_num_vs_devs)) {
> + tty_unregister_driver(ttyvs_driver);
> + put_tty_driver(ttyvs_driver);
> +
> + max_num_vs_devs = max_num;
> + ret = vs_register_with_tty_core();
> + if (ret)
> + return ret;
> + }
> +
> + /*
> + * If we fail to create any device emit error log and move to
> + * the next dt node.
> + */
> + for_each_available_child_of_node(np, child) {
> + if (of_node_test_and_set_flag(child, OF_POPULATED))
> + continue;
> +
> + if (of_property_read_u32(child, "peer-dev", &peer)) {
> + ret = vs_add_lb(NULL, child);
> + if (ret) {
> + pr_err("can't create lb %s %d\n",
> + child->name, ret);
> + continue;
> + }
> + } else {
> + peer_node = of_find_node_by_phandle(peer);
> + if (peer_node) {
> + of_node_set_flag(peer_node, OF_POPULATED);
> + ret = vs_add_nm(NULL, child, peer_node);
> + if (ret) {
> + pr_err("can't create nm %s <-> %s %d\n",
> + child->name, peer_node->name,
> + ret);
> + continue;
> + }
> + } else {
> + pr_err("can't find peer for %s %d\n",
> + child->name, ret);
> + }
> + }
> + }
> +
> + return 0;
> +}
> +
> +static inline struct vs_cfs_dev_info *to_vs_dinfo(
> + struct config_item *item)
> +{
> + return container_of(to_config_group(item),
> + struct vs_cfs_dev_info, grp);
> +}
> +
> +#define VS_DEV_ATTR_WR_U8(_name) \
> +static ssize_t vs_dev_##_name##_store(struct config_item *item, \
> + const char *page, size_t len) \
> +{ \
> + u8 val; \
> + int ret; \
> + ret = kstrtou8(page, 0, &val); \
> + if (ret) \
> + return ret; \
> + to_vs_dinfo(item)->_name = val; \
> + return len; \
> +} \
> +static ssize_t vs_dev_##_name##_show(struct config_item *item, \
> + char *buf) \
> +{ \
> + return snprintf(buf, PAGE_SIZE, "%u\n", to_vs_dinfo(item)->_name); \
> +}
> +
> +#define VS_DEV_ATTR_WR_U16(_name) \
> +static ssize_t vs_dev_##_name##_store(struct config_item *item, \
> + const char *page, size_t len) \
> +{ \
> + u16 val; \
> + int ret; \
> + ret = kstrtou16(page, 0, &val); \
> + if (ret) \
> + return ret; \
> + to_vs_dinfo(item)->_name = val; \
> + return len; \
> +} \
> +static ssize_t vs_dev_##_name##_show(struct config_item *item, \
> + char *buf) \
> +{ \
> + return snprintf(buf, PAGE_SIZE, "%u\n", to_vs_dinfo(item)->_name); \
> +}
> +
> +#define VS_DEV_ATTR_WR_STR(_name) \
> +static ssize_t vs_dev_##_name##_store(struct config_item *item, \
> + const char *page, size_t len) \
> +{ \
> + char *devtype; \
> + devtype = kstrdup(page, GFP_KERNEL); \
> + if (!devtype) \
> + return -ENOMEM; \
> + if (devtype[len - 1] == '\n') \
> + devtype[len - 1] = '\0'; \
> + to_vs_dinfo(item)->devtype = devtype; \
> + return len; \
> +} \
> +static ssize_t vs_dev_##_name##_show(struct config_item *item, \
> + char *buf) \
> +{ \
> + return snprintf(buf, PAGE_SIZE, "%s\n", to_vs_dinfo(item)->devtype); \
> +}
> +
> +/*
> + * Once all parameters for the device has been set, this finally
> + * creates the device.
> + */
> +static ssize_t vs_dev_create_store(struct config_item *item,
> + const char *page, size_t len)
> +{
> + u8 val;
> + int ret;
> + struct vs_cfs_dev_info *di;
> +
> + ret = kstrtou8(page, 0, &val);
> + if (ret)
> + return ret;
> +
> + /* User must write 1 to this node create device */
> + if (val != 1)
> + return -EINVAL;
> +
> + di = to_vs_dinfo(item);
> +
> + /* devtype must be defined to proceed further */
> + if (!di->devtype)
> + return -EINVAL;
> +
> + if (strncmp(di->devtype, "lb", 2) == 0)
> + ret = vs_add_lb(di, NULL);
> + else if (strncmp(di->devtype, "nm", 2) == 0)
> + ret = vs_add_nm(di, NULL, NULL);
> + else
> + return -EINVAL;
> +
> + if (ret)
> + return ret;
> + return len;
> +}
> +
> +VS_DEV_ATTR_WR_STR(devtype)
> +VS_DEV_ATTR_WR_U16(ownidx)
> +VS_DEV_ATTR_WR_U16(peeridx)
> +VS_DEV_ATTR_WR_U8(ortsmap)
> +VS_DEV_ATTR_WR_U8(odtrmap)
> +VS_DEV_ATTR_WR_U8(odtratopn)
> +VS_DEV_ATTR_WR_U8(prtsmap)
> +VS_DEV_ATTR_WR_U8(pdtrmap)
> +VS_DEV_ATTR_WR_U8(pdtratopn)
> +
> +CONFIGFS_ATTR(vs_dev_, devtype);
> +CONFIGFS_ATTR(vs_dev_, ownidx);
> +CONFIGFS_ATTR(vs_dev_, ortsmap);
> +CONFIGFS_ATTR(vs_dev_, odtrmap);
> +CONFIGFS_ATTR(vs_dev_, odtratopn);
> +CONFIGFS_ATTR(vs_dev_, peeridx);
> +CONFIGFS_ATTR(vs_dev_, prtsmap);
> +CONFIGFS_ATTR(vs_dev_, pdtrmap);
> +CONFIGFS_ATTR(vs_dev_, pdtratopn);
> +CONFIGFS_ATTR_WO(vs_dev_, create);
> +
> +static struct configfs_attribute *vs_dev_attrs[] = {
> + &vs_dev_attr_devtype,
> + &vs_dev_attr_ownidx,
> + &vs_dev_attr_ortsmap,
> + &vs_dev_attr_odtrmap,
> + &vs_dev_attr_odtratopn,
> + &vs_dev_attr_peeridx,
> + &vs_dev_attr_prtsmap,
> + &vs_dev_attr_pdtrmap,
> + &vs_dev_attr_pdtratopn,
> + &vs_dev_attr_create,
> + NULL,
> +};
> +
> +static const struct config_item_type vs_cfs_root_type = {
> + .ct_attrs = vs_dev_attrs,
> + .ct_owner = THIS_MODULE,
> +};
> +
> +static struct config_group *vs_cfs_grp_make(
> + struct config_group *group,
> + const char *name)
> +{
> + struct vs_cfs_dev_info *di;
> +
> + di = kzalloc(sizeof(*di), GFP_KERNEL);
> + if (!di)
> + return ERR_PTR(-ENOMEM);
> +
> + config_group_init_type_name(&di->grp, name, &vs_cfs_root_type);
> +
> + return &di->grp;
> +}
> +
> +static void vs_cfs_grp_drop(struct config_group *group,
> + struct config_item *item)
> +{
> + struct vs_cfs_dev_info *di = to_vs_dinfo(item);
> +
> + mutex_lock(&card_lock);
> + vs_del_specific_devs(di->ownidx, 1);
> + mutex_unlock(&card_lock);
> +
> + kfree(di);
> + config_item_put(item);
> +}
> +
> +static struct configfs_group_operations vs_cfs_grp_ops = {
> + .make_group = &vs_cfs_grp_make,
> + .drop_item = &vs_cfs_grp_drop,
> +};
> +
> +static const struct config_item_type vs_cfs_grp_type = {
> + .ct_group_ops = &vs_cfs_grp_ops,
> + .ct_owner = THIS_MODULE,
> +};
> +
> +struct configfs_subsystem vs_cfs_subsys = {
> + .su_group = {
> + .cg_item = {
> + .ci_namebuf = "ttyvs",
> + .ci_type = &vs_cfs_grp_type,
> + },
> + },
> + .su_mutex = __MUTEX_INITIALIZER(vs_cfs_subsys.su_mutex),
> +};
> +
> +static const struct of_device_id ttyvs_dev_match_tbl[] = {
> + { .compatible = "ttyvs,virtual-uart-card" },
> + { }
> +};
> +MODULE_DEVICE_TABLE(of, ttyvs_dev_match_tbl);
> +
> +static struct platform_driver ttyvs_platform_drv = {
> + .probe = ttyvs_device_probe,
> + .driver = {
> + .name = "ttyvs",
> + .of_match_table = ttyvs_dev_match_tbl,
> + },
> +};
> +
> +static int __init ttyvs_init(void)
> +{
> + int ret;
> +
> + config_group_init(&vs_cfs_subsys.su_group);
> +
> + ret = configfs_register_subsystem(&vs_cfs_subsys);
> + if (ret)
> + return ret;
> +
> + ret = vs_register_with_tty_core();
> + if (ret)
> + goto fail_drv;
> +
> + /* Register as platform driver to handle device tree nodes */
> + ret = platform_driver_register(&ttyvs_platform_drv);
> + if (ret)
> + goto fail_plat;
> +
> + pr_info("serial port null modem emulation driver\n");
> + return 0;
> +
> +fail_plat:
> + tty_unregister_driver(ttyvs_driver);
> + put_tty_driver(ttyvs_driver);
> +
> +fail_drv:
> + configfs_unregister_subsystem(&vs_cfs_subsys);
> +
> + return ret;
> +}
> +
> +static void __exit ttyvs_exit(void)
> +{
> + vs_del_all_devs();
> +
> + configfs_unregister_subsystem(&vs_cfs_subsys);
> + platform_driver_unregister(&ttyvs_platform_drv);
> +
> + tty_unregister_driver(ttyvs_driver);
> + put_tty_driver(ttyvs_driver);
> +}
> +
> +module_init(ttyvs_init);
> +module_exit(ttyvs_exit);
> +
> +/*
> + * By default this driver supports upto 64 virtual devices. This
> + * can be overridden through max_num_vs_devs module parameter or
> + * through max-num-vs-devs device tree property.
> + */
> +module_param(max_num_vs_devs, ushort, 0);
> +MODULE_PARM_DESC(max_num_vs_devs,
> + "Maximum virtual tty devices to be supported");
> +
> +MODULE_AUTHOR("Rishi Gupta <gupt21@...il.com>");
> +MODULE_DESCRIPTION("Serial port null modem emulation driver");
> +MODULE_LICENSE("GPL v2");
> --
> 2.7.4
>
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