* artpec.c / serial_core.c hardware flow control problem
@ 2012-06-28 15:29 Mikael Johansson
2012-06-28 16:24 ` Alan Cox
0 siblings, 1 reply; 4+ messages in thread
From: Mikael Johansson @ 2012-06-28 15:29 UTC (permalink / raw)
To: linux-serial; +Cc: Mikael Starvik, Jesper Nilsson, Johan Adolfsson
Greetings,
We have a problem with drivers/serial/artpec.c (Not yet in main tree)
which uses hardware supported flow control (XON/XOFF). We do cfmakeraw()
and tcsetattr() from userspace to set a termios struct where (c_iflag &
IXON) is not set. The problem is that the call to tcsetattr() is not
propagated down to serial_artpec_set_termios(), the reason being that
uart_set_termios() doesn't think that IXON is a RELEVANT_IFLAG and
returns prematurely instead of calling uart_change_speed -->
ops->set_termios().
Could this be fixed by making IXON a RELEVANT_IFLAG?:
diff --git a/drivers/serial/serial_core.c b/drivers/serial/serial_core.c
index 7f28307..d45473d 100644
--- a/drivers/serial/serial_core.c
+++ b/drivers/serial/serial_core.c
@@ -1211,7 +1211,7 @@ static void uart_set_termios(struct tty_struct *tty,
* bits in c_cflag; c_[io]speed will always be set
* appropriately by set_termios() in tty_ioctl.c
*/
-#define RELEVANT_IFLAG(iflag) ((iflag) &
(IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK))
+#define RELEVANT_IFLAG(iflag) ((iflag) &
(IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK|IXON))
if ((cflag ^ old_termios->c_cflag) == 0 &&
tty->termios->c_ospeed == old_termios->c_ospeed &&
tty->termios->c_ispeed == old_termios->c_ispeed &&
Or should it be fixed at some other level?
Note: This was tested on 2.6.35 but appears to have the same code in the
newer kernels. Not many drivers seem to look at the IXON flag, only
crisv10, omap_serial and jsm_neo.
Best regards,
Mikael Johansson
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: artpec.c / serial_core.c hardware flow control problem
2012-06-28 15:29 artpec.c / serial_core.c hardware flow control problem Mikael Johansson
@ 2012-06-28 16:24 ` Alan Cox
2012-06-29 15:16 ` Johan Adolfsson
0 siblings, 1 reply; 4+ messages in thread
From: Alan Cox @ 2012-06-28 16:24 UTC (permalink / raw)
To: Mikael Johansson
Cc: linux-serial, Mikael Starvik, Jesper Nilsson, Johan Adolfsson
On Thu, 28 Jun 2012 17:29:27 +0200
Mikael Johansson <mikael.lars.johansson@axis.com> wrote:
> Greetings,
>
> We have a problem with drivers/serial/artpec.c (Not yet in main tree)
> which uses hardware supported flow control (XON/XOFF). We do cfmakeraw()
> and tcsetattr() from userspace to set a termios struct where (c_iflag &
> IXON) is not set. The problem is that the call to tcsetattr() is not
> propagated down to serial_artpec_set_termios(), the reason being that
> uart_set_termios() doesn't think that IXON is a RELEVANT_IFLAG and
> returns prematurely instead of calling uart_change_speed -->
> ops->set_termios().
>
> Could this be fixed by making IXON a RELEVANT_IFLAG?:
That's actually insufficient for those cases - you can set the characters
used for things as well plus IXANY and IXOFF.
It's a stupid "optimisation" and the only reason I didn't get rid of it
before was in case it broke something else. Time for it to go.
So yeah - I'd just delete it.
If you are doing hardware XON/XOFF watch c_cc[VSTART] and c_cc[VSTOP].
Those control the symbol used for soft flow control.
Alan
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: artpec.c / serial_core.c hardware flow control problem
2012-06-28 16:24 ` Alan Cox
@ 2012-06-29 15:16 ` Johan Adolfsson
2012-06-29 16:31 ` Alan Cox
0 siblings, 1 reply; 4+ messages in thread
From: Johan Adolfsson @ 2012-06-29 15:16 UTC (permalink / raw)
To: Alan Cox, Mikael Lars Johansson
Cc: linux-serial, Mikael Starvik, Jesper Nilsson, Johan Adolfsson
> -----Original Message-----
> From: linux-serial-owner@vger.kernel.org [mailto:linux-serial-
> owner@vger.kernel.org] On Behalf Of Alan Cox
> Sent: den 28 juni 2012 18:24
>
> On Thu, 28 Jun 2012 17:29:27 +0200
> Mikael Johansson <mikael.lars.johansson@axis.com> wrote:
>
> > Greetings,
> >
> > We have a problem with drivers/serial/artpec.c (Not yet in main tree)
> > which uses hardware supported flow control (XON/XOFF). We do
> cfmakeraw()
> > and tcsetattr() from userspace to set a termios struct where (c_iflag
> &
> > IXON) is not set. The problem is that the call to tcsetattr() is not
> > propagated down to serial_artpec_set_termios(), the reason being that
> > uart_set_termios() doesn't think that IXON is a RELEVANT_IFLAG and
> > returns prematurely instead of calling uart_change_speed -->
> > ops->set_termios().
> >
> > Could this be fixed by making IXON a RELEVANT_IFLAG?:
>
> That's actually insufficient for those cases - you can set the
> characters
> used for things as well plus IXANY and IXOFF.
>
> It's a stupid "optimisation" and the only reason I didn't get rid of it
> before was in case it broke something else. Time for it to go.
>
> So yeah - I'd just delete it.
Do you mean the entire if () { return; } statement or just the RELEVANT_IFLAG part?
> If you are doing hardware XON/XOFF watch c_cc[VSTART] and c_cc[VSTOP].
> Those control the symbol used for soft flow control.
We use STOP_CHAR(tty), we only have hardware support for stopping transfer,
the tty layer kicks in and enables it again.
> Alan
/Johan
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: artpec.c / serial_core.c hardware flow control problem
2012-06-29 15:16 ` Johan Adolfsson
@ 2012-06-29 16:31 ` Alan Cox
0 siblings, 0 replies; 4+ messages in thread
From: Alan Cox @ 2012-06-29 16:31 UTC (permalink / raw)
To: Johan Adolfsson
Cc: Mikael Lars Johansson, linux-serial, Mikael Starvik,
Jesper Nilsson, Johan Adolfsson
> Do you mean the entire if () { return; } statement or just the RELEVANT_IFLAG part?
It's not enough to check the iflag in this case - a termios changing
c_cc[VSTOP) - which is what STOP_CHAR(tty) is, also might need
the stop handling reprogramming.
Alan
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2012-06-29 16:27 UTC | newest]
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2012-06-28 15:29 artpec.c / serial_core.c hardware flow control problem Mikael Johansson
2012-06-28 16:24 ` Alan Cox
2012-06-29 15:16 ` Johan Adolfsson
2012-06-29 16:31 ` Alan Cox
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