[patch v2 1/1] staging: speakup: flush tty buffers and ensure hardware flow control

[Okash Khawaja]

This patch fixes the issue where TTY-migrated synths would take a while to shut up after hitting numpad enter key. When calling synth_flush, even though XOFF character is sent as high priority, data buffered in TTY layer is still sent to the synth. This patch flushes that buffered data when synth_flush is called.

It also tries to ensure that hardware flow control is enabled, by setting CRTSCTS using tty's termios.

Reported-by: John Covici <covici@xxxxxxxxxxxxxx>
Signed-off-by: Okash Khawaja <okash.khawaja@xxxxxxxxx>
Reviewed-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>

Index: linux-staging/drivers/staging/speakup/serialio.c
===================================================================
--- linux-staging.orig/drivers/staging/speakup/serialio.c
+++ linux-staging/drivers/staging/speakup/serialio.c
@@ -30,6 +30,7 @@
 static void spk_serial_tiocmset(unsigned int set, unsigned int clear);
 static unsigned char spk_serial_in(void);
 static unsigned char spk_serial_in_nowait(void);
+static void spk_serial_flush_buffer(void);
 
 struct spk_io_ops spk_serial_io_ops = {
 	.synth_out = spk_serial_out,
@@ -37,6 +38,7 @@
 	.tiocmset = spk_serial_tiocmset,
 	.synth_in = spk_serial_in,
 	.synth_in_nowait = spk_serial_in_nowait,
+	.flush_buffer = spk_serial_flush_buffer,
 };
 EXPORT_SYMBOL_GPL(spk_serial_io_ops);
 
@@ -268,6 +270,11 @@
 	return inb_p(speakup_info.port_tts + UART_RX);
 }
 
+static void spk_serial_flush_buffer(void)
+{
+	/* TODO: flush the UART 16550 buffer */
+}
+
 static int spk_serial_out(struct spk_synth *in_synth, const char ch)
 {
 	if (in_synth->alive && spk_wait_for_xmitr(in_synth)) {
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
@@ -85,6 +85,7 @@
 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);
+static void spk_ttyio_flush_buffer(void);
 
 struct spk_io_ops spk_ttyio_ops = {
 	.synth_out = spk_ttyio_out,
@@ -92,13 +93,22 @@
 	.tiocmset = spk_ttyio_tiocmset,
 	.synth_in = spk_ttyio_in,
 	.synth_in_nowait = spk_ttyio_in_nowait,
+	.flush_buffer = spk_ttyio_flush_buffer,
 };
 EXPORT_SYMBOL_GPL(spk_ttyio_ops);
 
+static inline void get_termios(struct tty_struct *tty, struct ktermios *out_termios)
+{
+	down_read(&tty->termios_rwsem);
+	*out_termios = tty->termios;
+	up_read(&tty->termios_rwsem);
+}
+
 static int spk_ttyio_initialise_ldisc(int ser)
 {
 	int ret = 0;
 	struct tty_struct *tty;
+	struct ktermios tmp_termios;
 
 	ret = tty_register_ldisc(N_SPEAKUP, &spk_ttyio_ldisc_ops);
 	if (ret) {
@@ -127,6 +137,20 @@
 	}
 
 	clear_bit(TTY_HUPPED, &tty->flags);
+	/* ensure hardware flow control is enabled */
+	get_termios(tty, &tmp_termios);
+	if (!(tmp_termios.c_cflag & CRTSCTS)) {
+		tmp_termios.c_cflag |= CRTSCTS;
+		tty_set_termios(tty, &tmp_termios);
+		/* 
+		 * check c_cflag to see if it's updated as tty_set_termios may not return
+		 * error even when no tty bits are changed by the request.
+		 */
+		get_termios(tty, &tmp_termios);
+		if (!(tmp_termios.c_cflag & CRTSCTS))
+			pr_warn("speakup: Failed to set hardware flow control\n");
+	}
+
 	tty_unlock(tty);
 
 	ret = tty_set_ldisc(tty, N_SPEAKUP);
@@ -201,6 +225,11 @@
 	return (rv == 0xff) ? 0 : rv;
 }
 
+static void spk_ttyio_flush_buffer(void)
+{
+	speakup_tty->ops->flush_buffer(speakup_tty);
+}
+
 int spk_ttyio_synth_probe(struct spk_synth *synth)
 {
 	int rv = spk_ttyio_initialise_ldisc(synth->ser);
Index: linux-staging/drivers/staging/speakup/spk_types.h
===================================================================
--- linux-staging.orig/drivers/staging/speakup/spk_types.h
+++ linux-staging/drivers/staging/speakup/spk_types.h
@@ -154,6 +154,7 @@
 	void (*tiocmset)(unsigned int set, unsigned int clear);
 	unsigned char (*synth_in)(void);
 	unsigned char (*synth_in_nowait)(void);
+	void (*flush_buffer)(void);
 };
 
 struct spk_synth {
Index: linux-staging/drivers/staging/speakup/speakup_audptr.c
===================================================================
--- linux-staging.orig/drivers/staging/speakup/speakup_audptr.c
+++ linux-staging/drivers/staging/speakup/speakup_audptr.c
@@ -127,6 +127,7 @@
 
 static void synth_flush(struct spk_synth *synth)
 {
+	synth->io_ops->flush_buffer();
 	synth->io_ops->send_xchar(SYNTH_CLEAR);
 	synth->io_ops->synth_out(synth, PROCSPEECH);
 }
Index: linux-staging/drivers/staging/speakup/speakup_decext.c
===================================================================
--- linux-staging.orig/drivers/staging/speakup/speakup_decext.c
+++ linux-staging/drivers/staging/speakup/speakup_decext.c
@@ -221,6 +221,7 @@
 static void synth_flush(struct spk_synth *synth)
 {
 	in_escape = 0;
+	synth->io_ops->flush_buffer();
 	synth->synth_immediate(synth, "\033P;10z\033\\");
 }
 
Index: linux-staging/drivers/staging/speakup/speakup_dectlk.c
===================================================================
--- linux-staging.orig/drivers/staging/speakup/speakup_dectlk.c
+++ linux-staging/drivers/staging/speakup/speakup_dectlk.c
@@ -293,6 +293,7 @@
 		synth->io_ops->synth_out(synth, ']');
 	in_escape = 0;
 	is_flushing = 1;
+	synth->io_ops->flush_buffer();
 	synth->io_ops->synth_out(synth, SYNTH_CLEAR);
 }
 
Index: linux-staging/drivers/staging/speakup/speakup_spkout.c
===================================================================
--- linux-staging.orig/drivers/staging/speakup/speakup_spkout.c
+++ linux-staging/drivers/staging/speakup/speakup_spkout.c
@@ -125,6 +125,7 @@
 
 static void synth_flush(struct spk_synth *synth)
 {
+	synth->io_ops->flush_buffer();
 	synth->io_ops->send_xchar(SYNTH_CLEAR);
 }
 
Index: linux-staging/drivers/staging/speakup/synth.c
===================================================================
--- linux-staging.orig/drivers/staging/speakup/synth.c
+++ linux-staging/drivers/staging/speakup/synth.c
@@ -120,6 +120,7 @@
 
 void spk_synth_flush(struct spk_synth *synth)
 {
+	synth->io_ops->flush_buffer();
 	synth->io_ops->synth_out(synth, synth->clear);
 }
 EXPORT_SYMBOL_GPL(spk_synth_flush);