staging: speakup: add send_xchar, tiocmset and input functionality for tty

[Okash Khawaja]

This patch adds further TTY-based functionality, specifically implementation
of send_xchar and tiocmset methods, and input. send_xchar and tiocmset
methods simply delegate to corresponding TTY operations.

For input, it implements the receive_buf2 callback in tty_ldisc_ops of
speakup's ldisc. If a synth defines read_buff_add method then receive_buf2
simply delegates to that and returns.

For spk_ttyio_in, the data is passed from receive_buf2 thread to
spk_ttyio_in thread through spk_ldisc_data structure. It has following
members:

- char buf: represents data received
- struct semaphore sem: used to signal to spk_ttyio_in thread that data
	is available to be read without having to busy wait
- bool buf_free: this is used in comination with mb() calls to syncronise
	the two threads over buf

receive_buf2 only writes to buf if buf_free is true. The check for buf_free
and writing to buf are separated by mb() to ensure that spk_ttyio_in has read
buf before receive_buf2 writes to it. After writing, it ups the semaphore to
signal to spk_ttyio_in that there is now data to read.

spk_ttyio_in waits for data to read by downing the semaphore. Thus when
signalled by receive_buf2 thread above, it reads from buf and sets buf_free
to true. These two operations are separated by mb() to ensure that
receive_buf2 thread finds buf_free to be true only after buf has been read.
After that spk_ttyio_in calls tty_schedule_flip for subsequent data to come
in through receive_buf2.

Signed-off-by: Okash Khawaja <okash.khawaja at gmail.com>

Index: linux-staging/drivers/staging/speakup/spk_ttyio.c
===================================================================
--- linux-staging.orig/drivers/staging/speakup/spk_ttyio.c
+++ linux-staging/drivers/staging/speakup/spk_ttyio.c
@@ -1,36 +1,97 @@
 #include <linux/types.h>
 #include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/slab.h>
 
 #include "speakup.h"
 #include "spk_types.h"
+#include "spk_priv.h"
 
+struct spk_ldisc_data {
+	char buf;
+	struct semaphore sem;
+	bool buf_free;
+};
+
+static struct spk_synth *spk_ttyio_synth;
 static struct tty_struct *speakup_tty;
 
 static int spk_ttyio_ldisc_open(struct tty_struct *tty)
 {
+	struct spk_ldisc_data *ldisc_data;
+
 	if (tty->ops->write == NULL)
 		return -EOPNOTSUPP;
 	speakup_tty = tty;
 
+	ldisc_data = kmalloc(sizeof(struct spk_ldisc_data), GFP_KERNEL);
+	if (!ldisc_data) {
+		pr_err("speakup: Failed to allocate ldisc_data.\n");
+		return -ENOMEM;
+	}
+
+	sema_init(&ldisc_data->sem, 0);
+	ldisc_data->buf_free = true;
+	speakup_tty->disc_data = ldisc_data;
+
 	return 0;
 }
 
 static void spk_ttyio_ldisc_close(struct tty_struct *tty)
 {
+	kfree(speakup_tty->disc_data);
 	speakup_tty = NULL;
 }
 
+static int spk_ttyio_receive_buf2(struct tty_struct *tty,
+		const unsigned char *cp, char *fp, int count)
+{
+	struct spk_ldisc_data *ldisc_data = tty->disc_data;
+
+	if (spk_ttyio_synth->read_buff_add) {
+		int i;
+		for (i = 0; i < count; i++)
+			spk_ttyio_synth->read_buff_add(cp[i]);
+
+		return count;
+	}
+
+	if (!ldisc_data->buf_free)
+		/* ttyio_in will tty_schedule_flip */
+		return 0;
+
+	/* Make sure the consumer has read buf before we have seen
+         * buf_free == true and overwrite buf */
+	mb();
+
+	ldisc_data->buf = cp[0];
+	ldisc_data->buf_free = false;
+	up(&ldisc_data->sem);
+
+	return 1;
+}
+
 static struct tty_ldisc_ops spk_ttyio_ldisc_ops = {
 	.owner          = THIS_MODULE,
 	.magic          = TTY_LDISC_MAGIC,
 	.name           = "speakup_ldisc",
 	.open           = spk_ttyio_ldisc_open,
 	.close          = spk_ttyio_ldisc_close,
+	.receive_buf2	= spk_ttyio_receive_buf2,
 };
 
 static int spk_ttyio_out(struct spk_synth *in_synth, const char ch);
+static void spk_ttyio_send_xchar(char ch);
+static void spk_ttyio_tiocmset(unsigned int set, unsigned int clear);
+static unsigned char spk_ttyio_in(void);
+static unsigned char spk_ttyio_in_nowait(void);
+
 struct spk_io_ops spk_ttyio_ops = {
 	.synth_out = spk_ttyio_out,
+	.send_xchar = spk_ttyio_send_xchar,
+	.tiocmset = spk_ttyio_tiocmset,
+	.synth_in = spk_ttyio_in,
+	.synth_in_nowait = spk_ttyio_in_nowait,
 };
 EXPORT_SYMBOL_GPL(spk_ttyio_ops);
 
@@ -95,6 +156,48 @@
 	return 0;
 }
 
+static void spk_ttyio_send_xchar(char ch)
+{
+	speakup_tty->ops->send_xchar(speakup_tty, ch);
+}
+
+static void spk_ttyio_tiocmset(unsigned int set, unsigned int clear)
+{
+	speakup_tty->ops->tiocmset(speakup_tty, set, clear);
+}
+
+static unsigned char ttyio_in(int timeout)
+{
+	struct spk_ldisc_data *ldisc_data = speakup_tty->disc_data;
+	char rv;
+
+	if (down_timeout(&ldisc_data->sem, usecs_to_jiffies(timeout)) != 0) {
+		pr_warn("spk_ttyio: timeout (%d)  while waiting for input\n",
+				timeout);
+		return 0xff;
+	}
+
+	rv = ldisc_data->buf;
+	/* Make sure we have read buf before we set buf_free to let
+	 * the producer overwrite it */
+	mb();
+	ldisc_data->buf_free = true;
+	/* Let TTY push more characters */
+	tty_schedule_flip(speakup_tty->port);
+
+	return rv;
+}
+
+static unsigned char spk_ttyio_in(void)
+{
+	return ttyio_in(SPK_SYNTH_TIMEOUT);
+}
+
+static unsigned char spk_ttyio_in_nowait(void)
+{
+	return ttyio_in(0);
+}
+
 int spk_ttyio_synth_probe(struct spk_synth *synth)
 {
 	int rv = spk_ttyio_initialise_ldisc(synth->ser);
@@ -103,6 +206,7 @@
 		return rv;
 
 	synth->alive = 1;
+	spk_ttyio_synth = synth;
 
 	return 0;
 }
Index: linux-staging/drivers/staging/speakup/serialio.h
===================================================================
--- linux-staging.orig/drivers/staging/speakup/serialio.h
+++ linux-staging/drivers/staging/speakup/serialio.h
@@ -8,6 +8,8 @@
 #endif
 #include <linux/serial_core.h>
 
+#include "spk_priv.h"
+
 /*
  * this is cut&paste from 8250.h. Get rid of the structure, the definitions
  * and this whole broken driver.
@@ -21,7 +23,7 @@
 };
 
 /* countdown values for serial timeouts in us */
-#define SPK_SERIAL_TIMEOUT 100000
+#define SPK_SERIAL_TIMEOUT SPK_SYNTH_TIMEOUT
 /* countdown values transmitter/dsr timeouts in us */
 #define SPK_XMITR_TIMEOUT 100000
 /* countdown values cts timeouts in us */
Index: linux-staging/drivers/staging/speakup/spk_priv.h
===================================================================
--- linux-staging.orig/drivers/staging/speakup/spk_priv.h
+++ linux-staging/drivers/staging/speakup/spk_priv.h
@@ -39,6 +39,7 @@
 #endif
 
 #define KT_SPKUP 15
+#define SPK_SYNTH_TIMEOUT 100000 /* in micro-seconds */
 
 const struct old_serial_port *spk_serial_init(int index);
 void spk_stop_serial_interrupt(void);