Date:	Mon, 14 Jan 2013 10:54:55 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	James Hogan <james.hogan@...tec.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Cesar Eduardo Barros <cesarb@...arb.net>,
	Joe Perches <joe@...ches.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v3 43/44] tty/metag_da: Add metag DA TTY driver

Here's a new version addressing Jiri's feedback.

Add a TTY driver for communicating over a Meta DA (Debug Adapter)
channel using the bios channel SWITCH operation.

Signed-off-by: James Hogan <james.hogan@...tec.com>
Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Mauro Carvalho Chehab <mchehab@...hat.com>
Cc: Cesar Eduardo Barros <cesarb@...arb.net>
Cc: Joe Perches <joe@...ches.com>
Cc: "David S. Miller" <davem@...emloft.net>
---
 MAINTAINERS                            |    1 +
 arch/metag/Kconfig                     |    4 +-
 arch/metag/configs/meta1_defconfig     |    2 +
 arch/metag/configs/meta2_defconfig     |    2 +
 arch/metag/configs/meta2_smp_defconfig |    2 +
 arch/metag/kernel/setup.c              |   12 +
 drivers/tty/Kconfig                    |   13 +
 drivers/tty/Makefile                   |    1 +
 drivers/tty/metag_da.c                 |  679 ++++++++++++++++++++++++++++++++
 9 files changed, 715 insertions(+), 1 deletions(-)
 create mode 100644 drivers/tty/metag_da.c

diff --git a/MAINTAINERS b/MAINTAINERS
index dbc2bd6..63ccab6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5002,6 +5002,7 @@ S:	Supported
 F:	arch/metag/
 F:	Documentation/metag/
 F:	Documentation/devicetree/bindings/metag/
+F:	drivers/tty/metag_da.c
 
 MICROBLAZE ARCHITECTURE
 M:	Michal Simek <monstr@...str.eu>
diff --git a/arch/metag/Kconfig b/arch/metag/Kconfig
index 9bd0bc1..f4ef3bb 100644
--- a/arch/metag/Kconfig
+++ b/arch/metag/Kconfig
@@ -221,7 +221,9 @@ config METAG_DA
 	  of the DA will be detected automatically at boot, so it is safe to say
 	  Y to this option even when booting without a DA.
 
-	  This enables support for services provided by DA JTAG debug adapters.
+	  This enables support for services provided by DA JTAG debug adapters,
+	  such as:
+	  - communication over DA channels (such as the console driver).
 
 menu "Boot options"
 
diff --git a/arch/metag/configs/meta1_defconfig b/arch/metag/configs/meta1_defconfig
index 0773425..ad663ca 100644
--- a/arch/metag/configs/meta1_defconfig
+++ b/arch/metag/configs/meta1_defconfig
@@ -28,6 +28,8 @@ CONFIG_BLK_DEV_RAM_SIZE=16384
 # CONFIG_SERIO is not set
 # CONFIG_VT is not set
 # CONFIG_LEGACY_PTYS is not set
+CONFIG_DA_TTY=y
+CONFIG_DA_CONSOLE=y
 # CONFIG_DEVKMEM is not set
 # CONFIG_HW_RANDOM is not set
 # CONFIG_HWMON is not set
diff --git a/arch/metag/configs/meta2_defconfig b/arch/metag/configs/meta2_defconfig
index 001f9bf..47922e93 100644
--- a/arch/metag/configs/meta2_defconfig
+++ b/arch/metag/configs/meta2_defconfig
@@ -29,6 +29,8 @@ CONFIG_BLK_DEV_RAM_SIZE=16384
 # CONFIG_SERIO is not set
 # CONFIG_VT is not set
 # CONFIG_LEGACY_PTYS is not set
+CONFIG_DA_TTY=y
+CONFIG_DA_CONSOLE=y
 # CONFIG_DEVKMEM is not set
 # CONFIG_HW_RANDOM is not set
 # CONFIG_HWMON is not set
diff --git a/arch/metag/configs/meta2_smp_defconfig b/arch/metag/configs/meta2_smp_defconfig
index d6f7e46..f508250 100644
--- a/arch/metag/configs/meta2_smp_defconfig
+++ b/arch/metag/configs/meta2_smp_defconfig
@@ -30,6 +30,8 @@ CONFIG_BLK_DEV_RAM_SIZE=16384
 # CONFIG_SERIO is not set
 # CONFIG_VT is not set
 # CONFIG_LEGACY_PTYS is not set
+CONFIG_DA_TTY=y
+CONFIG_DA_CONSOLE=y
 # CONFIG_DEVKMEM is not set
 # CONFIG_HW_RANDOM is not set
 # CONFIG_HWMON is not set
diff --git a/arch/metag/kernel/setup.c b/arch/metag/kernel/setup.c
index 1410db0..0d46334 100644
--- a/arch/metag/kernel/setup.c
+++ b/arch/metag/kernel/setup.c
@@ -61,6 +61,11 @@ extern char _heap_start[];
 extern u32 __dtb_start[];
 #endif
 
+#ifdef CONFIG_DA_CONSOLE
+/* Our early channel based console driver */
+extern struct console dash_console;
+#endif
+
 struct machine_desc *machine_desc __initdata;
 
 /*
@@ -182,6 +187,13 @@ void __init setup_arch(char **cmdline_p)
 	metag_cache_probe();
 
 	metag_da_probe();
+#ifdef CONFIG_DA_CONSOLE
+	if (metag_da_enabled()) {
+		/* An early channel based console driver */
+		register_console(&dash_console);
+		add_preferred_console("ttyDA", 1, NULL);
+	}
+#endif
 
 	/* try interpreting the argument as a device tree */
 	machine_desc = setup_machine_fdt(original_cmd_line);
diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 0ecf22b..5eef53d 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -388,3 +388,16 @@ config PPC_EARLY_DEBUG_EHV_BC_HANDLE
 	  If the number you specify is not a valid byte channel handle, then
 	  there simply will be no early console output.  This is true also
 	  if you don't boot under a hypervisor at all.
+
+config DA_TTY
+	bool "DA TTY"
+	depends on METAG_DA
+	select SERIAL_NONSTANDARD
+	help
+	  This enables a TTY on a Dash channel.
+
+config DA_CONSOLE
+	bool "DA Console"
+	depends on DA_TTY
+	help
+	  This enables a console on a Dash channel.
diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index 2953059..dbd7745 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -27,5 +27,6 @@ obj-$(CONFIG_SYNCLINK_GT)	+= synclink_gt.o
 obj-$(CONFIG_SYNCLINKMP)	+= synclinkmp.o
 obj-$(CONFIG_SYNCLINK)		+= synclink.o
 obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o
+obj-$(CONFIG_DA_TTY)	+= metag_da.o
 
 obj-y += ipwireless/
diff --git a/drivers/tty/metag_da.c b/drivers/tty/metag_da.c
new file mode 100644
index 0000000..6a0b2e6
--- /dev/null
+++ b/drivers/tty/metag_da.c
@@ -0,0 +1,679 @@
+/*
+ *  dashtty.c - tty driver for Dash channels interface.
+ *
+ *  Copyright (C) 2007,2008,2012 Imagination Technologies
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ *
+ */
+
+#include <linux/atomic.h>
+#include <linux/completion.h>
+#include <linux/console.h>
+#include <linux/delay.h>
+#include <linux/export.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/kthread.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/serial.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/timer.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/tty_flip.h>
+#include <linux/uaccess.h>
+
+#include <asm/da.h>
+
+/* Channel error codes */
+#define CONAOK	0
+#define CONERR	1
+#define CONBAD	2
+#define CONPRM	3
+#define CONADR	4
+#define CONCNT	5
+#define CONCBF	6
+#define CONCBE	7
+#define CONBSY	8
+
+/* Default channel for the console */
+#define CONSOLE_CHANNEL      1
+
+#define NUM_TTY_CHANNELS     6
+
+/* Auto allocate */
+#define DA_TTY_MAJOR        0
+
+/* A speedy poll rate helps the userland debug process connection response.
+ * But, if you set it too high then no other userland processes get much
+ * of a look in.
+ */
+#define DA_TTY_POLL (HZ / 50)
+
+/*
+ * A short put delay improves latency but has a high throughput overhead
+ */
+#define DA_TTY_PUT_DELAY (HZ / 100)
+
+static atomic_t num_channels_need_poll = ATOMIC_INIT(0);
+
+static struct timer_list poll_timer;
+
+static struct tty_driver *channel_driver;
+
+static struct timer_list put_timer;
+static struct task_struct *dashtty_thread;
+
+#define RX_BUF_SIZE 1024
+
+enum {
+	INCHR = 1,
+	OUTCHR,
+	RDBUF,
+	WRBUF,
+	RDSTAT
+};
+
+/**
+ * struct dashtty_port - Wrapper struct for dashtty tty_port.
+ * @port:		TTY port data
+ * @rx_lock:		Lock for rx_buf.
+ *			This protects between the poll timer and user context.
+ *			It's also held during read SWITCH operations.
+ * @rx_buf:		Read buffer
+ * @xmit_lock:		Lock for xmit_*, and port.xmit_buf.
+ *			This protects between user context and kernel thread.
+ *			It's also held during write SWITCH operations.
+ * @xmit_cnt:		Size of xmit buffer contents
+ * @xmit_head:		Head of xmit buffer where data is written
+ * @xmit_tail:		Tail of xmit buffer where data is read
+ * @xmit_empty:		Completion for xmit buffer being empty
+ */
+struct dashtty_port {
+	struct tty_port		 port;
+	spinlock_t		 rx_lock;
+	void			*rx_buf;
+	struct mutex		 xmit_lock;
+	unsigned int		 xmit_cnt;
+	unsigned int		 xmit_head;
+	unsigned int		 xmit_tail;
+	struct completion	 xmit_empty;
+};
+
+static struct dashtty_port dashtty_ports[NUM_TTY_CHANNELS];
+
+static atomic_t dashtty_xmit_cnt = ATOMIC_INIT(0);
+static wait_queue_head_t dashtty_waitqueue;
+
+/*
+ * Low-level DA channel access routines
+ */
+static int chancall(int in_bios_function, int in_channel,
+		    int in_arg2, void *in_arg3,
+		    void *in_arg4)
+{
+	register int   bios_function asm("D1Ar1") = in_bios_function;
+	register int   channel       asm("D0Ar2") = in_channel;
+	register int   arg2          asm("D1Ar3") = in_arg2;
+	register void *arg3          asm("D0Ar4") = in_arg3;
+	register void *arg4          asm("D1Ar5") = in_arg4;
+	register int   bios_call     asm("D0Ar6") = 3;
+	register int   result        asm("D0Re0");
+
+	asm volatile (
+		"MSETL	[A0StP++], %6,%4,%2\n\t"
+		"ADD	A0StP, A0StP, #8\n\t"
+		"SWITCH	#0x0C30208\n\t"
+		"GETD	%0, [A0StP+#-8]\n\t"
+		"SUB	A0StP, A0StP, #(4*6)+8\n\t"
+		: "=d" (result)   /* outs */
+		: "d" (bios_function),
+		  "d" (channel),
+		  "d" (arg2),
+		  "d" (arg3),
+		  "d" (arg4),
+		  "d" (bios_call) /* ins */
+		: "memory");
+
+	return result;
+}
+
+/*
+ * Attempts to fetch count bytes from channel and returns actual count.
+ */
+static int fetch_data(struct tty_struct *tty)
+{
+	unsigned int channel = tty->index;
+	struct dashtty_port *dport = &dashtty_ports[channel];
+	int received = 0;
+
+	spin_lock_bh(&dport->rx_lock);
+	/* check the port isn't being shut down */
+	if (!dport->rx_buf)
+		goto unlock;
+	if (chancall(RDBUF, channel, RX_BUF_SIZE,
+		     (void *)dport->rx_buf, &received) == CONAOK) {
+		if (received) {
+			int space;
+			unsigned char *cbuf;
+
+			space = tty_prepare_flip_string(tty, &cbuf, received);
+
+			if (space <= 0)
+				goto unlock;
+
+			memcpy(cbuf, dport->rx_buf, space);
+			tty_flip_buffer_push(tty);
+		}
+	}
+unlock:
+	spin_unlock_bh(&dport->rx_lock);
+
+	return received;
+}
+
+/**
+ * find_channel_to_poll() - Returns kref to the next channel tty to poll.
+ * Returns:	The TTY of the next channel to poll, or NULL if no TTY needs
+ *		polling. Release with tty_kref_put().
+ */
+static struct tty_struct *find_channel_to_poll(void)
+{
+	static int last_polled_channel;
+	int last = last_polled_channel;
+	int chan;
+	struct tty_struct *tty = NULL;
+
+	for (chan = last + 1; ; ++chan) {
+		if (chan >= NUM_TTY_CHANNELS)
+			chan = 0;
+
+		tty = tty_port_tty_get(&dashtty_ports[chan].port);
+		if (tty) {
+			last_polled_channel = chan;
+			return tty;
+		}
+
+		if (chan == last)
+			break;
+	}
+	return tty;
+}
+
+/**
+ * put_channel_data() - Write out a block of channel data.
+ * @chan:	DA channel number.
+ *
+ * Write a single block of data out to the debug adapter. If the circular buffer
+ * is wrapped then only the first block is written.
+ *
+ * Returns:	1 if the remote buffer was too full to accept data.
+ *		0 otherwise.
+ */
+static int put_channel_data(unsigned int chan)
+{
+	struct dashtty_port *dport;
+	struct tty_struct *tty;
+	int number_written;
+	unsigned int count = 0;
+
+	dport = &dashtty_ports[chan];
+	mutex_lock(&dport->xmit_lock);
+	if (dport->xmit_cnt) {
+		count = min((unsigned int)(SERIAL_XMIT_SIZE - dport->xmit_tail),
+			    dport->xmit_cnt);
+		chancall(WRBUF, chan, count,
+			 dport->port.xmit_buf + dport->xmit_tail,
+			 &number_written);
+		dport->xmit_cnt -= number_written;
+		if (!dport->xmit_cnt) {
+			/* reset pointers to avoid wraps */
+			dport->xmit_head = 0;
+			dport->xmit_tail = 0;
+			complete(&dport->xmit_empty);
+		} else {
+			dport->xmit_tail += number_written;
+			if (dport->xmit_tail >= SERIAL_XMIT_SIZE)
+				dport->xmit_tail -= SERIAL_XMIT_SIZE;
+		}
+		atomic_sub(number_written, &dashtty_xmit_cnt);
+	}
+	mutex_unlock(&dport->xmit_lock);
+
+	/* if we've made more data available, wake up tty */
+	if (count && number_written) {
+		tty = tty_port_tty_get(&dport->port);
+		if (tty) {
+			tty_wakeup(tty);
+			tty_kref_put(tty);
+		}
+	}
+
+	/* did the write fail? */
+	return count && !number_written;
+}
+
+/**
+ * put_data() - Kernel thread to write out blocks of channel data to DA.
+ * @arg:	Unused.
+ *
+ * This kernel thread runs while @dashtty_xmit_cnt != 0, and loops over the
+ * channels to write out any buffered data. If any of the channels stall due to
+ * the remote buffer being full, a hold off happens to allow the debugger to
+ * drain the buffer.
+ */
+static int put_data(void *arg)
+{
+	unsigned int chan, stall;
+
+	__set_current_state(TASK_RUNNING);
+	while (!kthread_should_stop()) {
+		/*
+		 * For each channel see if there's anything to transmit in the
+		 * port's xmit_buf.
+		 */
+		stall = 0;
+		for (chan = 0; chan < NUM_TTY_CHANNELS; ++chan)
+			stall += put_channel_data(chan);
+
+		/*
+		 * If some of the buffers are full, hold off for a short while
+		 * to allow them to empty.
+		 */
+		if (stall)
+			msleep(25);
+
+		wait_event_interruptible(dashtty_waitqueue,
+					 atomic_read(&dashtty_xmit_cnt));
+	}
+
+	return 0;
+}
+
+/*
+ *	This gets called every DA_TTY_POLL and polls the channels for data
+ */
+static void dashtty_timer(unsigned long ignored)
+{
+	struct tty_struct *tty;
+
+	/* If there are no ports open do nothing and don't poll again. */
+	if (!atomic_read(&num_channels_need_poll))
+		return;
+
+	tty = find_channel_to_poll();
+
+	/* Did we find a channel to poll? */
+	if (tty) {
+		fetch_data(tty);
+		tty_kref_put(tty);
+	}
+
+	mod_timer_pinned(&poll_timer, jiffies + DA_TTY_POLL);
+}
+
+static void add_poll_timer(struct timer_list *poll_timer)
+{
+	setup_timer(poll_timer, dashtty_timer, 0);
+	poll_timer->expires = jiffies + DA_TTY_POLL;
+
+	/*
+	 * Always attach the timer to the boot CPU. The DA channels are per-CPU
+	 * so all polling should be from a single CPU.
+	 */
+	add_timer_on(poll_timer, 0);
+}
+
+static int dashtty_port_activate(struct tty_port *port, struct tty_struct *tty)
+{
+	struct dashtty_port *dport = container_of(port, struct dashtty_port,
+						  port);
+	void *rx_buf;
+
+	/* Allocate the buffer we use for writing data */
+	if (tty_port_alloc_xmit_buf(port) < 0)
+		goto err;
+
+	/* Allocate the buffer we use for reading data */
+	rx_buf = kzalloc(RX_BUF_SIZE, GFP_KERNEL);
+	if (!rx_buf)
+		goto err_free_xmit;
+
+	spin_lock_bh(&dport->rx_lock);
+	dport->rx_buf = rx_buf;
+	spin_unlock_bh(&dport->rx_lock);
+
+	/*
+	 * Don't add the poll timer if we're opening a console. This
+	 * avoids the overhead of polling the Dash but means it is not
+	 * possible to have a login on /dev/console.
+	 *
+	 */
+	if (dport != &dashtty_ports[CONSOLE_CHANNEL])
+		if (atomic_inc_return(&num_channels_need_poll) == 1)
+			add_poll_timer(&poll_timer);
+
+	return 0;
+err_free_xmit:
+	tty_port_free_xmit_buf(port);
+err:
+	return -ENOMEM;
+}
+
+static void dashtty_port_shutdown(struct tty_port *port)
+{
+	struct dashtty_port *dport = container_of(port, struct dashtty_port,
+						  port);
+	void *rx_buf;
+	unsigned int count;
+
+	/* stop reading */
+	if (dport != &dashtty_ports[CONSOLE_CHANNEL])
+		if (atomic_dec_and_test(&num_channels_need_poll))
+			del_timer_sync(&poll_timer);
+
+	mutex_lock(&dport->xmit_lock);
+	count = dport->xmit_cnt;
+	mutex_unlock(&dport->xmit_lock);
+	if (count) {
+		/*
+		 * There's still data to write out, so wake and wait for the
+		 * writer thread to drain the buffer.
+		 */
+		del_timer(&put_timer);
+		wake_up_interruptible(&dashtty_waitqueue);
+		wait_for_completion(&dport->xmit_empty);
+	}
+
+	/* Null the read buffer (timer could still be running!) */
+	spin_lock_bh(&dport->rx_lock);
+	rx_buf = dport->rx_buf;
+	dport->rx_buf = NULL;
+	spin_unlock_bh(&dport->rx_lock);
+	/* Free the read buffer */
+	kfree(rx_buf);
+
+	/* Free the write buffer */
+	tty_port_free_xmit_buf(port);
+}
+
+static const struct tty_port_operations dashtty_port_ops = {
+	.activate	= dashtty_port_activate,
+	.shutdown	= dashtty_port_shutdown,
+};
+
+static int dashtty_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	return tty_port_install(&dashtty_ports[tty->index].port, driver, tty);
+}
+
+static int dashtty_open(struct tty_struct *tty, struct file *filp)
+{
+	return tty_port_open(tty->port, tty, filp);
+}
+
+static void dashtty_close(struct tty_struct *tty, struct file *filp)
+{
+	return tty_port_close(tty->port, tty, filp);
+}
+
+static void dashtty_hangup(struct tty_struct *tty)
+{
+	int channel;
+	struct dashtty_port *dport;
+
+	channel = tty->index;
+	dport = &dashtty_ports[channel];
+
+	/* drop any data in the xmit buffer */
+	mutex_lock(&dport->xmit_lock);
+	if (dport->xmit_cnt) {
+		atomic_sub(dport->xmit_cnt, &dashtty_xmit_cnt);
+		dport->xmit_cnt = 0;
+		dport->xmit_head = 0;
+		dport->xmit_tail = 0;
+		complete(&dport->xmit_empty);
+	}
+	mutex_unlock(&dport->xmit_lock);
+
+	tty_port_hangup(tty->port);
+}
+
+/**
+ * dashtty_put_timer() - Delayed wake up of kernel thread.
+ * @ignored:	unused
+ *
+ * This timer function wakes up the kernel thread if any data exists in the
+ * buffers. It is used to delay the expensive writeout until the writer has
+ * stopped writing.
+ */
+static void dashtty_put_timer(unsigned long ignored)
+{
+	if (atomic_read(&dashtty_xmit_cnt))
+		wake_up_interruptible(&dashtty_waitqueue);
+}
+
+static int dashtty_write(struct tty_struct *tty, const unsigned char *buf,
+			 int total)
+{
+	int channel, count, block;
+	struct dashtty_port *dport;
+
+	/* Determine the channel */
+	channel = tty->index;
+	dport = &dashtty_ports[channel];
+
+	/*
+	 * Write to output buffer.
+	 *
+	 * The reason that we asynchronously write the buffer is because if we
+	 * were to write the buffer synchronously then because DA channels are
+	 * per-CPU the buffer would be written to the channel of whatever CPU
+	 * we're running on.
+	 *
+	 * What we actually want to happen is have all input and output done on
+	 * one CPU.
+	 */
+	mutex_lock(&dport->xmit_lock);
+	/* work out how many bytes we can write to the xmit buffer */
+	total = min(total, (int)(SERIAL_XMIT_SIZE - dport->xmit_cnt));
+	atomic_add(total, &dashtty_xmit_cnt);
+	dport->xmit_cnt += total;
+	/* write the actual bytes (may need splitting if it wraps) */
+	for (count = total; count; count -= block) {
+		block = min(count, (int)(SERIAL_XMIT_SIZE - dport->xmit_head));
+		memcpy(dport->port.xmit_buf + dport->xmit_head, buf, block);
+		dport->xmit_head += block;
+		if (dport->xmit_head >= SERIAL_XMIT_SIZE)
+			dport->xmit_head -= SERIAL_XMIT_SIZE;
+		buf += block;
+	}
+	count = dport->xmit_cnt;
+	/* xmit buffer no longer empty? */
+	if (count)
+		INIT_COMPLETION(dport->xmit_empty);
+	mutex_unlock(&dport->xmit_lock);
+
+	if (total) {
+		/*
+		 * If the buffer is full, wake up the kthread, otherwise allow
+		 * some more time for the buffer to fill up a bit before waking
+		 * it.
+		 */
+		if (count == SERIAL_XMIT_SIZE) {
+			del_timer(&put_timer);
+			wake_up_interruptible(&dashtty_waitqueue);
+		} else {
+			mod_timer(&put_timer, jiffies + DA_TTY_PUT_DELAY);
+		}
+	}
+	return total;
+}
+
+static int dashtty_write_room(struct tty_struct *tty)
+{
+	struct dashtty_port *dport;
+	int channel;
+	int room;
+
+	channel = tty->index;
+	dport = &dashtty_ports[channel];
+
+	/* report the space in the xmit buffer */
+	mutex_lock(&dport->xmit_lock);
+	room = SERIAL_XMIT_SIZE - dport->xmit_cnt;
+	mutex_unlock(&dport->xmit_lock);
+
+	return room;
+}
+
+static int dashtty_chars_in_buffer(struct tty_struct *tty)
+{
+	struct dashtty_port *dport;
+	int channel;
+	int chars;
+
+	channel = tty->index;
+	dport = &dashtty_ports[channel];
+
+	/* report the number of bytes in the xmit buffer */
+	mutex_lock(&dport->xmit_lock);
+	chars = dport->xmit_cnt;
+	mutex_unlock(&dport->xmit_lock);
+
+	return chars;
+}
+
+static const struct tty_operations dashtty_ops = {
+	.install		= dashtty_install,
+	.open			= dashtty_open,
+	.close			= dashtty_close,
+	.hangup			= dashtty_hangup,
+	.write			= dashtty_write,
+	.write_room		= dashtty_write_room,
+	.chars_in_buffer	= dashtty_chars_in_buffer,
+};
+
+static int __init dashtty_init(void)
+{
+	int ret;
+	int nport;
+	struct dashtty_port *dport;
+
+	if (!metag_da_enabled())
+		return -ENODEV;
+
+	channel_driver = tty_alloc_driver(NUM_TTY_CHANNELS,
+					  TTY_DRIVER_REAL_RAW);
+	if (IS_ERR(channel_driver))
+		return PTR_ERR(channel_driver);
+
+	channel_driver->driver_name = "metag_da";
+	channel_driver->name = "ttyDA";
+	channel_driver->major = DA_TTY_MAJOR;
+	channel_driver->minor_start = 0;
+	channel_driver->type = TTY_DRIVER_TYPE_SERIAL;
+	channel_driver->subtype = SERIAL_TYPE_NORMAL;
+	channel_driver->init_termios = tty_std_termios;
+	channel_driver->init_termios.c_cflag |= CLOCAL;
+
+	tty_set_operations(channel_driver, &dashtty_ops);
+	for (nport = 0; nport < NUM_TTY_CHANNELS; nport++) {
+		dport = &dashtty_ports[nport];
+		tty_port_init(&dport->port);
+		dport->port.ops = &dashtty_port_ops;
+		spin_lock_init(&dport->rx_lock);
+		mutex_init(&dport->xmit_lock);
+		/* the xmit buffer starts empty, i.e. completely written */
+		init_completion(&dport->xmit_empty);
+		complete(&dport->xmit_empty);
+	}
+
+	setup_timer(&put_timer, dashtty_put_timer, 0);
+
+	init_waitqueue_head(&dashtty_waitqueue);
+	dashtty_thread = kthread_create(put_data, NULL, "ttyDA");
+	if (IS_ERR(dashtty_thread)) {
+		pr_err("Couldn't create dashtty thread\n");
+		ret = PTR_ERR(dashtty_thread);
+		goto err_destroy_ports;
+	}
+	/*
+	 * Bind the writer thread to the boot CPU so it can't migrate.
+	 * DA channels are per-CPU and we want all channel I/O to be on a single
+	 * predictable CPU.
+	 */
+	kthread_bind(dashtty_thread, 0);
+	wake_up_process(dashtty_thread);
+
+	ret = tty_register_driver(channel_driver);
+
+	if (ret < 0) {
+		pr_err("Couldn't install dashtty driver: err %d\n",
+		       ret);
+		goto err_stop_kthread;
+	}
+
+	return 0;
+
+err_stop_kthread:
+	kthread_stop(dashtty_thread);
+err_destroy_ports:
+	for (nport = 0; nport < NUM_TTY_CHANNELS; nport++) {
+		dport = &dashtty_ports[nport];
+		tty_port_destroy(&dport->port);
+	}
+	put_tty_driver(channel_driver);
+	return ret;
+}
+
+static void dashtty_exit(void)
+{
+	int nport;
+	struct dashtty_port *dport;
+
+	del_timer_sync(&put_timer);
+	kthread_stop(dashtty_thread);
+	del_timer_sync(&poll_timer);
+	tty_unregister_driver(channel_driver);
+	for (nport = 0; nport < NUM_TTY_CHANNELS; nport++) {
+		dport = &dashtty_ports[nport];
+		tty_port_destroy(&dport->port);
+	}
+	put_tty_driver(channel_driver);
+}
+
+module_init(dashtty_init);
+module_exit(dashtty_exit);
+
+#ifdef CONFIG_DA_CONSOLE
+
+static void dash_console_write(struct console *co, const char *s,
+			       unsigned int count)
+{
+	int actually_written;
+
+	chancall(WRBUF, CONSOLE_CHANNEL, count, (void *)s, &actually_written);
+}
+
+static struct tty_driver *dash_console_device(struct console *c, int *index)
+{
+	*index = c->index;
+	return channel_driver;
+}
+
+struct console dash_console = {
+	.name = "ttyDA",
+	.write = dash_console_write,
+	.device = dash_console_device,
+	.flags = CON_PRINTBUFFER,
+	.index = 1,
+};
+
+#endif
-- 
1.7.7.6



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