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[patch 0/1] staging: speakup: flush tty buffers and ensure hardware flow control

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  [patch 0/1] staging: speakup: flush tty buffers and ensure hardware flow control okash.khawaja@gmail.com - 2017-05-09 14:50 +0200
    [patch 1/1] staging: speakup: flush tty buffers and ensure hardware flow control okash.khawaja@gmail.com - 2017-05-09 14:50 +0200
      Re: [patch 1/1] staging: speakup: flush tty buffers and ensure  hardware flow control Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-05-10 21:50 +0200
        Re: [patch 1/1] staging: speakup: flush tty buffers and ensure  hardware flow control Okash Khawaja <okash.khawaja@gmail.com> - 2017-05-11 10:40 +0200
          Re: [patch 1/1] staging: speakup: flush tty buffers and ensure  hardware flow control Alan Cox <gnomes@lxorguk.ukuu.org.uk> - 2017-05-11 15:40 +0200

#1638102 — [patch 0/1] staging: speakup: flush tty buffers and ensure hardware flow control

Hi,

This patch applies on top of previous patchset which migrates synths to TTY [1]. It fixes couple of issues and tries to ensure hardware flow control is enabled.

Thanks,
Okash

[1] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1387738.html

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#1638104 — [patch 1/1] staging: speakup: flush tty buffers and ensure hardware flow control

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@ccs.covici.com>
Signed-off-by: Okash Khawaja <okash.khawaja@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

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,
@@ -92,6 +93,7 @@
 	.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);
 
@@ -99,6 +101,7 @@
 {
 	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 +130,18 @@
 	}
 
 	clear_bit(TTY_HUPPED, &tty->flags);
+	/* ensure hardware flow control is enabled */
+	down_read(&tty->termios_rwsem);
+	tmp_termios = tty->termios;
+	up_read(&tty->termios_rwsem);
+
+	if (!(tmp_termios.c_cflag & CRTSCTS)) {
+		tmp_termios.c_cflag |= CRTSCTS;
+		ret = tty_set_termios(tty, &tmp_termios);
+		if (ret)
+			pr_warn("speakup: Failed to set hardware flow control\n");
+	}
+
 	tty_unlock(tty);
 
 	ret = tty_set_ldisc(tty, N_SPEAKUP);
@@ -201,6 +216,11 @@
 	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);

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#1639058 — Re: [patch 1/1] staging: speakup: flush tty buffers and ensure hardware flow control

> +	if (!(tmp_termios.c_cflag & CRTSCTS)) {
> +		tmp_termios.c_cflag |= CRTSCTS;
> +		ret = tty_set_termios(tty, &tmp_termios);
> +		if (ret)
> +			pr_warn("speakup: Failed to set hardware flow control\n");

You should check the tty c_cflag after the call rather than rely on an
error code. Strictly speaking tty_set_termios should error if no tty bits
are changed by the request but it never has on Linux. Instead check the
tty gave you the result you wanted.

Alan

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#1639245 — Re: [patch 1/1] staging: speakup: flush tty buffers and ensure hardware flow control

Hi Alan,

On Wed, May 10, 2017 at 08:41:51PM +0100, Alan Cox wrote:
> > +	if (!(tmp_termios.c_cflag & CRTSCTS)) {
> > +		tmp_termios.c_cflag |= CRTSCTS;
> > +		ret = tty_set_termios(tty, &tmp_termios);
> > +		if (ret)
> > +			pr_warn("speakup: Failed to set hardware flow control\n");
> 
> You should check the tty c_cflag after the call rather than rely on an
> error code. Strictly speaking tty_set_termios should error if no tty bits
> are changed by the request but it never has on Linux. Instead check the
> tty gave you the result you wanted.
Thanks. I will replace the check for return value with check for c_cflag.

May be we should fix this in tty_set_termios?

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#1639440 — Re: [patch 1/1] staging: speakup: flush tty buffers and ensure hardware flow control

On Thu, 11 May 2017 09:29:14 +0100
Okash Khawaja <okash.khawaja@gmail.com> wrote:

> Hi Alan,
> 
> On Wed, May 10, 2017 at 08:41:51PM +0100, Alan Cox wrote:
> > > +	if (!(tmp_termios.c_cflag & CRTSCTS)) {
> > > +		tmp_termios.c_cflag |= CRTSCTS;
> > > +		ret = tty_set_termios(tty, &tmp_termios);
> > > +		if (ret)
> > > +			pr_warn("speakup: Failed to set hardware flow control\n");  
> > 
> > You should check the tty c_cflag after the call rather than rely on an
> > error code. Strictly speaking tty_set_termios should error if no tty bits
> > are changed by the request but it never has on Linux. Instead check the
> > tty gave you the result you wanted.  
> Thanks. I will replace the check for return value with check for c_cflag.
> 
> May be we should fix this in tty_set_termios?

Possibly. It however changes the external kernel ABI. It's also not a
simple memcmp because any undefined bits must be ignored.

Make a patch, try it and see what breaks ? If nothing breaks then yes it
makes sense IMHO too.

Alan

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