tty: bfin_jtag_comm: emulate a TTY over the Blackfin EMUDAT/JTAG interface

The Blackfin JTAG interface has a 4 byte generic data field (EMUDAT).  With
a little creative thinking, we can turn this into a TTY device.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/Kconfig

@@ -97,6 +97,19 @@ config DEVKMEM
 	  kind of kernel debugging operations.
 	  When in doubt, say "N".
 
+config BFIN_JTAG_COMM
+	tristate "Blackfin JTAG Communication"
+	depends on BLACKFIN
+	help
+	  Add support for emulating a TTY device over the Blackfin JTAG.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called bfin_jtag_comm.
+
+config BFIN_JTAG_COMM_CONSOLE
+	bool "Console on Blackfin JTAG"
+	depends on BFIN_JTAG_COMM=y
+
 config SERIAL_NONSTANDARD
 	bool "Non-standard serial port support"
 	depends on HAS_IOMEM

drivers/char/Makefile

@@ -13,6 +13,7 @@ obj-$(CONFIG_LEGACY_PTYS)	+= pty.o
 obj-$(CONFIG_UNIX98_PTYS)	+= pty.o
 obj-y				+= misc.o
 obj-$(CONFIG_VT)		+= vt_ioctl.o vc_screen.o selection.o keyboard.o
+obj-$(CONFIG_BFIN_JTAG_COMM)	+= bfin_jtag_comm.o
 obj-$(CONFIG_CONSOLE_TRANSLATIONS) += consolemap.o consolemap_deftbl.o
 obj-$(CONFIG_HW_CONSOLE)	+= vt.o defkeymap.o
 obj-$(CONFIG_AUDIT)		+= tty_audit.o

drivers/char/bfin_jtag_comm.c

@@ -0,0 +1,365 @@
+/*
+ * TTY over Blackfin JTAG Communication
+ *
+ * Copyright 2008-2009 Analog Devices Inc.
+ *
+ * Enter bugs at http://blackfin.uclinux.org/
+ *
+ * Licensed under the GPL-2 or later.
+ */
+
+#include <linux/circ_buf.h>
+#include <linux/console.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/kthread.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/tty_flip.h>
+#include <asm/atomic.h>
+
+/* See the Debug/Emulation chapter in the HRM */
+#define EMUDOF   0x00000001	/* EMUDAT_OUT full & valid */
+#define EMUDIF   0x00000002	/* EMUDAT_IN full & valid */
+#define EMUDOOVF 0x00000004	/* EMUDAT_OUT overflow */
+#define EMUDIOVF 0x00000008	/* EMUDAT_IN overflow */
+
+#define DRV_NAME "bfin-jtag-comm"
+#define DEV_NAME "ttyBFJC"
+
+#define pr_init(fmt, args...) ({ static const __initdata char __fmt[] = fmt; printk(__fmt, ## args); })
+#define debug(fmt, args...) pr_debug(DRV_NAME ": " fmt, ## args)
+
+static inline uint32_t bfin_write_emudat(uint32_t emudat)
+{
+	__asm__ __volatile__("emudat = %0;" : : "d"(emudat));
+	return emudat;
+}
+
+static inline uint32_t bfin_read_emudat(void)
+{
+	uint32_t emudat;
+	__asm__ __volatile__("%0 = emudat;" : "=d"(emudat));
+	return emudat;
+}
+
+static inline uint32_t bfin_write_emudat_chars(char a, char b, char c, char d)
+{
+	return bfin_write_emudat((a << 0) | (b << 8) | (c << 16) | (d << 24));
+}
+
+#define CIRC_SIZE 2048	/* see comment in tty_io.c:do_tty_write() */
+#define CIRC_MASK (CIRC_SIZE - 1)
+#define circ_empty(circ)     ((circ)->head == (circ)->tail)
+#define circ_free(circ)      CIRC_SPACE((circ)->head, (circ)->tail, CIRC_SIZE)
+#define circ_cnt(circ)       CIRC_CNT((circ)->head, (circ)->tail, CIRC_SIZE)
+#define circ_byte(circ, idx) ((circ)->buf[(idx) & CIRC_MASK])
+
+static struct tty_driver *bfin_jc_driver;
+static struct task_struct *bfin_jc_kthread;
+static struct tty_struct * volatile bfin_jc_tty;
+static unsigned long bfin_jc_count;
+static DEFINE_MUTEX(bfin_jc_tty_mutex);
+static volatile struct circ_buf bfin_jc_write_buf;
+
+static int
+bfin_jc_emudat_manager(void *arg)
+{
+	uint32_t inbound_len = 0, outbound_len = 0;
+
+	while (!kthread_should_stop()) {
+		/* no one left to give data to, so sleep */
+		if (bfin_jc_tty == NULL && circ_empty(&bfin_jc_write_buf)) {
+			debug("waiting for readers\n");
+			__set_current_state(TASK_UNINTERRUPTIBLE);
+			schedule();
+			__set_current_state(TASK_RUNNING);
+		}
+
+		/* no data available, so just chill */
+		if (!(bfin_read_DBGSTAT() & EMUDIF) && circ_empty(&bfin_jc_write_buf)) {
+			debug("waiting for data (in_len = %i) (circ: %i %i)\n",
+				inbound_len, bfin_jc_write_buf.tail, bfin_jc_write_buf.head);
+			if (inbound_len)
+				schedule();
+			else
+				schedule_timeout_interruptible(HZ);
+			continue;
+		}
+
+		/* if incoming data is ready, eat it */
+		if (bfin_read_DBGSTAT() & EMUDIF) {
+			struct tty_struct *tty;
+			mutex_lock(&bfin_jc_tty_mutex);
+			tty = (struct tty_struct *)bfin_jc_tty;
+			if (tty != NULL) {
+				uint32_t emudat = bfin_read_emudat();
+				if (inbound_len == 0) {
+					debug("incoming length: 0x%08x\n", emudat);
+					inbound_len = emudat;
+				} else {
+					size_t num_chars = (4 <= inbound_len ? 4 : inbound_len);
+					debug("  incoming data: 0x%08x (pushing %zu)\n", emudat, num_chars);
+					inbound_len -= num_chars;
+					tty_insert_flip_string(tty, (unsigned char *)&emudat, num_chars);
+					tty_flip_buffer_push(tty);
+				}
+			}
+			mutex_unlock(&bfin_jc_tty_mutex);
+		}
+
+		/* if outgoing data is ready, post it */
+		if (!(bfin_read_DBGSTAT() & EMUDOF) && !circ_empty(&bfin_jc_write_buf)) {
+			if (outbound_len == 0) {
+				outbound_len = circ_cnt(&bfin_jc_write_buf);
+				bfin_write_emudat(outbound_len);
+				debug("outgoing length: 0x%08x\n", outbound_len);
+			} else {
+				struct tty_struct *tty;
+				int tail = bfin_jc_write_buf.tail;
+				size_t ate = (4 <= outbound_len ? 4 : outbound_len);
+				uint32_t emudat =
+				bfin_write_emudat_chars(
+					circ_byte(&bfin_jc_write_buf, tail + 0),
+					circ_byte(&bfin_jc_write_buf, tail + 1),
+					circ_byte(&bfin_jc_write_buf, tail + 2),
+					circ_byte(&bfin_jc_write_buf, tail + 3)
+				);
+				bfin_jc_write_buf.tail += ate;
+				outbound_len -= ate;
+				mutex_lock(&bfin_jc_tty_mutex);
+				tty = (struct tty_struct *)bfin_jc_tty;
+				if (tty)
+					tty_wakeup(tty);
+				mutex_unlock(&bfin_jc_tty_mutex);
+				debug("  outgoing data: 0x%08x (pushing %zu)\n", emudat, ate);
+			}
+		}
+	}
+
+	__set_current_state(TASK_RUNNING);
+	return 0;
+}
+
+static int
+bfin_jc_open(struct tty_struct *tty, struct file *filp)
+{
+	mutex_lock(&bfin_jc_tty_mutex);
+	debug("open %lu\n", bfin_jc_count);
+	++bfin_jc_count;
+	bfin_jc_tty = tty;
+	wake_up_process(bfin_jc_kthread);
+	mutex_unlock(&bfin_jc_tty_mutex);
+	return 0;
+}
+
+static void
+bfin_jc_close(struct tty_struct *tty, struct file *filp)
+{
+	mutex_lock(&bfin_jc_tty_mutex);
+	debug("close %lu\n", bfin_jc_count);
+	if (--bfin_jc_count == 0)
+		bfin_jc_tty = NULL;
+	wake_up_process(bfin_jc_kthread);
+	mutex_unlock(&bfin_jc_tty_mutex);
+}
+
+/* XXX: we dont handle the put_char() case where we must handle count = 1 */
+static int
+bfin_jc_circ_write(const unsigned char *buf, int count)
+{
+	int i;
+	count = min(count, circ_free(&bfin_jc_write_buf));
+	debug("going to write chunk of %i bytes\n", count);
+	for (i = 0; i < count; ++i)
+		circ_byte(&bfin_jc_write_buf, bfin_jc_write_buf.head + i) = buf[i];
+	bfin_jc_write_buf.head += i;
+	return i;
+}
+
+#ifndef CONFIG_BFIN_JTAG_COMM_CONSOLE
+# define acquire_console_sem()
+# define release_console_sem()
+#endif
+static int
+bfin_jc_write(struct tty_struct *tty, const unsigned char *buf, int count)
+{
+	int i;
+	acquire_console_sem();
+	i = bfin_jc_circ_write(buf, count);
+	release_console_sem();
+	wake_up_process(bfin_jc_kthread);
+	return i;
+}
+
+static void
+bfin_jc_flush_chars(struct tty_struct *tty)
+{
+	wake_up_process(bfin_jc_kthread);
+}
+
+static int
+bfin_jc_write_room(struct tty_struct *tty)
+{
+	return circ_free(&bfin_jc_write_buf);
+}
+
+static int
+bfin_jc_chars_in_buffer(struct tty_struct *tty)
+{
+	return circ_cnt(&bfin_jc_write_buf);
+}
+
+static void
+bfin_jc_wait_until_sent(struct tty_struct *tty, int timeout)
+{
+	unsigned long expire = jiffies + timeout;
+	while (!circ_empty(&bfin_jc_write_buf)) {
+		if (signal_pending(current))
+			break;
+		if (time_after(jiffies, expire))
+			break;
+	}
+}
+
+static struct tty_operations bfin_jc_ops = {
+	.open            = bfin_jc_open,
+	.close           = bfin_jc_close,
+	.write           = bfin_jc_write,
+	/*.put_char        = bfin_jc_put_char,*/
+	.flush_chars     = bfin_jc_flush_chars,
+	.write_room      = bfin_jc_write_room,
+	.chars_in_buffer = bfin_jc_chars_in_buffer,
+	.wait_until_sent = bfin_jc_wait_until_sent,
+};
+
+static int __init bfin_jc_init(void)
+{
+	int ret;
+
+	bfin_jc_kthread = kthread_create(bfin_jc_emudat_manager, NULL, DRV_NAME);
+	if (IS_ERR(bfin_jc_kthread))
+		return PTR_ERR(bfin_jc_kthread);
+
+	ret = -ENOMEM;
+
+	bfin_jc_write_buf.head = bfin_jc_write_buf.tail = 0;
+	bfin_jc_write_buf.buf = kmalloc(CIRC_SIZE, GFP_KERNEL);
+	if (!bfin_jc_write_buf.buf)
+		goto err;
+
+	bfin_jc_driver = alloc_tty_driver(1);
+	if (!bfin_jc_driver)
+		goto err;
+
+	bfin_jc_driver->owner        = THIS_MODULE;
+	bfin_jc_driver->driver_name  = DRV_NAME;
+	bfin_jc_driver->name         = DEV_NAME;
+	bfin_jc_driver->type         = TTY_DRIVER_TYPE_SERIAL;
+	bfin_jc_driver->subtype      = SERIAL_TYPE_NORMAL;
+	bfin_jc_driver->init_termios = tty_std_termios;
+	tty_set_operations(bfin_jc_driver, &bfin_jc_ops);
+
+	ret = tty_register_driver(bfin_jc_driver);
+	if (ret)
+		goto err;
+
+	pr_init(KERN_INFO DRV_NAME ": initialized\n");
+
+	return 0;
+
+ err:
+	put_tty_driver(bfin_jc_driver);
+	kfree(bfin_jc_write_buf.buf);
+	kthread_stop(bfin_jc_kthread);
+	return ret;
+}
+module_init(bfin_jc_init);
+
+static void __exit bfin_jc_exit(void)
+{
+	kthread_stop(bfin_jc_kthread);
+	kfree(bfin_jc_write_buf.buf);
+	tty_unregister_driver(bfin_jc_driver);
+	put_tty_driver(bfin_jc_driver);
+}
+module_exit(bfin_jc_exit);
+
+#if defined(CONFIG_BFIN_JTAG_COMM_CONSOLE) || defined(CONFIG_EARLY_PRINTK)
+static void
+bfin_jc_straight_buffer_write(const char *buf, unsigned count)
+{
+	unsigned ate = 0;
+	while (bfin_read_DBGSTAT() & EMUDOF)
+		continue;
+	bfin_write_emudat(count);
+	while (ate < count) {
+		while (bfin_read_DBGSTAT() & EMUDOF)
+			continue;
+		bfin_write_emudat_chars(buf[ate], buf[ate+1], buf[ate+2], buf[ate+3]);
+		ate += 4;
+	}
+}
+#endif
+
+#ifdef CONFIG_BFIN_JTAG_COMM_CONSOLE
+static void
+bfin_jc_console_write(struct console *co, const char *buf, unsigned count)
+{
+	if (bfin_jc_kthread == NULL)
+		bfin_jc_straight_buffer_write(buf, count);
+	else
+		bfin_jc_circ_write(buf, count);
+}
+
+static struct tty_driver *
+bfin_jc_console_device(struct console *co, int *index)
+{
+	*index = co->index;
+	return bfin_jc_driver;
+}
+
+static struct console bfin_jc_console = {
+	.name    = DEV_NAME,
+	.write   = bfin_jc_console_write,
+	.device  = bfin_jc_console_device,
+	.flags   = CON_ANYTIME | CON_PRINTBUFFER,
+	.index   = -1,
+};
+
+static int __init bfin_jc_console_init(void)
+{
+	register_console(&bfin_jc_console);
+	return 0;
+}
+console_initcall(bfin_jc_console_init);
+#endif
+
+#ifdef CONFIG_EARLY_PRINTK
+static void __init
+bfin_jc_early_write(struct console *co, const char *buf, unsigned int count)
+{
+	bfin_jc_straight_buffer_write(buf, count);
+}
+
+static struct __initdata console bfin_jc_early_console = {
+	.name   = "early_BFJC",
+	.write   = bfin_jc_early_write,
+	.flags   = CON_ANYTIME | CON_PRINTBUFFER,
+	.index   = -1,
+};
+
+struct console * __init
+bfin_jc_early_init(unsigned int port, unsigned int cflag)
+{
+	return &bfin_jc_early_console;
+}
+#endif
+
+MODULE_AUTHOR("Mike Frysinger <vapier@gentoo.org>");
+MODULE_DESCRIPTION("TTY over Blackfin JTAG Communication");
+MODULE_LICENSE("GPL");