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Date:   Tue, 5 Oct 2021 14:59:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Jiri Slaby <jirislaby@...nel.org>, Suman Anna <s-anna@...com>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-remoteproc@...r.kernel.org
Subject: Re: [PATCH v8 2/2] tty: add rpmsg driver

On Thu, Sep 30, 2021 at 06:05:20PM +0200, Arnaud Pouliquen wrote:
> This driver exposes a standard TTY interface on top of the rpmsg
> framework through a rpmsg service.
> 
> This driver supports multi-instances, offering a /dev/ttyRPMSGx entry
> per rpmsg endpoint.
> 
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
> ---
>  Documentation/serial/tty_rpmsg.rst |  15 ++
>  drivers/tty/Kconfig                |   9 +
>  drivers/tty/Makefile               |   1 +
>  drivers/tty/rpmsg_tty.c            | 275 +++++++++++++++++++++++++++++
>  4 files changed, 300 insertions(+)
>  create mode 100644 Documentation/serial/tty_rpmsg.rst
>  create mode 100644 drivers/tty/rpmsg_tty.c
> 
> diff --git a/Documentation/serial/tty_rpmsg.rst b/Documentation/serial/tty_rpmsg.rst
> new file mode 100644
> index 000000000000..b055107866c9
> --- /dev/null
> +++ b/Documentation/serial/tty_rpmsg.rst
> @@ -0,0 +1,15 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========
> +RPMsg TTY
> +=========
> +
> +The rpmsg tty driver implements serial communication on the RPMsg bus to makes possible for
> +user-space programs to send and receive rpmsg messages as a standard tty protocol.
> +
> +The remote processor can instantiate a new tty by requesting a "rpmsg-tty" RPMsg service.
> +
> +The "rpmsg-tty" service is directly used for data exchange. No flow control is implemented.
> +
> +Information related to the RPMsg and associated tty device is available in
> +/sys/bus/rpmsg/devices/.


Why is this file needed?  Nothing references it, and this would be the
only file in this directory.

> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> index 23cc988c68a4..5095513029d7 100644
> --- a/drivers/tty/Kconfig
> +++ b/drivers/tty/Kconfig
> @@ -368,6 +368,15 @@ config VCC
>  
>  source "drivers/tty/hvc/Kconfig"
>  
> +config RPMSG_TTY
> +	tristate "RPMSG tty driver"
> +	depends on RPMSG
> +	help
> +	  Say y here to export rpmsg endpoints as tty devices, usually found
> +	  in /dev/ttyRPMSGx.
> +	  This makes it possible for user-space programs to send and receive
> +	  rpmsg messages as a standard tty protocol.

What is the module name going to be?


> +
>  endif # TTY
>  
>  source "drivers/tty/serdev/Kconfig"
> diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
> index a2bd75fbaaa4..07aca5184a55 100644
> --- a/drivers/tty/Makefile
> +++ b/drivers/tty/Makefile
> @@ -26,5 +26,6 @@ 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_VCC)		+= vcc.o
> +obj-$(CONFIG_RPMSG_TTY)		+= rpmsg_tty.o
>  
>  obj-y += ipwireless/
> diff --git a/drivers/tty/rpmsg_tty.c b/drivers/tty/rpmsg_tty.c
> new file mode 100644
> index 000000000000..0c99f54c2911
> --- /dev/null
> +++ b/drivers/tty/rpmsg_tty.c
> @@ -0,0 +1,275 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) STMicroelectronics 2021 - All Rights Reserved

Copyright needs a year, right?

> + */
> +
> +#include <linux/module.h>
> +#include <linux/rpmsg.h>
> +#include <linux/slab.h>
> +#include <linux/tty.h>
> +#include <linux/tty_flip.h>
> +
> +#define MAX_TTY_RPMSG	32

Why have a max at all?


> +
> +static DEFINE_IDR(tty_idr);	/* tty instance id */
> +static DEFINE_MUTEX(idr_lock);	/* protects tty_idr */

I didn't think an idr needed a lock anymore, are you sure this is
needed?


> +
> +static struct tty_driver *rpmsg_tty_driver;
> +
> +struct rpmsg_tty_port {
> +	struct tty_port		port;	 /* TTY port data */
> +	int			id;	 /* TTY rpmsg index */
> +	struct rpmsg_device	*rpdev;	 /* rpmsg device */
> +};
> +
> +static int rpmsg_tty_cb(struct rpmsg_device *rpdev, void *data, int len, void *priv, u32 src)
> +{
> +	struct rpmsg_tty_port *cport = dev_get_drvdata(&rpdev->dev);
> +	int copied;
> +
> +	if (!len)
> +		return -EINVAL;

How can len be 0?


> +	copied = tty_insert_flip_string(&cport->port, data, len);
> +	if (copied != len)
> +		dev_dbg(&rpdev->dev, "Trunc buffer: available space is %d\n",
> +			copied);

Is this the proper error handling?


> +	tty_flip_buffer_push(&cport->port);

Shouldn't you return the number of bytes sent?

> +
> +	return 0;
> +}
> +
> +static int rpmsg_tty_install(struct tty_driver *driver, struct tty_struct *tty)
> +{
> +	struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);
> +
> +	if (!cport) {
> +		dev_err(tty->dev, "Cannot get cport\n");

How can this happen?


> +		return -ENODEV;
> +	}
> +
> +	tty->driver_data = cport;
> +
> +	return tty_port_install(&cport->port, driver, tty);
> +}
> +
> +static int rpmsg_tty_open(struct tty_struct *tty, struct file *filp)
> +{
> +	return tty_port_open(tty->port, tty, filp);
> +}
> +
> +static void rpmsg_tty_close(struct tty_struct *tty, struct file *filp)
> +{
> +	return tty_port_close(tty->port, tty, filp);
> +}
> +
> +static int rpmsg_tty_write(struct tty_struct *tty, const u8 *buf, int len)
> +{
> +	struct rpmsg_tty_port *cport = tty->driver_data;
> +	struct rpmsg_device *rpdev;
> +	int msg_max_size, msg_size;
> +	int ret;
> +
> +	rpdev = cport->rpdev;
> +
> +	dev_dbg(&rpdev->dev, "Send msg from tty->index = %d, len = %d\n", tty->index, len);

ftrace is your friend, is this really still needed?

thanks,

greg k-h

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