linux-kernel - Re: [PATCH] USB: cdc-acm: only raise DTR on transitions from B0

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Date:	Wed, 29 Oct 2014 16:58:40 +0100
From:	Johan Hovold <johan@...nel.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Johan Hovold <johan@...nel.org>, linux-usb@...r.kernel.org,
	Jim Paris <jim@...n.com>, Oliver Neukum <oliver@...kum.org>,
	linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: Re: [PATCH] USB: cdc-acm: only raise DTR on transitions from B0

On Wed, Oct 29, 2014 at 11:56:02PM +0800, Greg Kroah-Hartman wrote:
> On Wed, Oct 29, 2014 at 04:30:40PM +0100, Johan Hovold wrote:
> > Make sure to only raise DTR on transitions from B0 in set_termios.
> > 
> > Also allow set_termios to be called from open with a termios_old of
> > NULL. Note that DTR will not be raised prematurely in this case.
> > 
> > Signed-off-by: Johan Hovold <johan@...nel.org>
> > ---
> >  drivers/usb/class/cdc-acm.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
> > index e934e19f49f5..7e58bbfd6319 100644
> > --- a/drivers/usb/class/cdc-acm.c
> > +++ b/drivers/usb/class/cdc-acm.c
> > @@ -980,11 +980,12 @@ static void acm_tty_set_termios(struct tty_struct *tty,
> >  	/* FIXME: Needs to clear unsupported bits in the termios */
> >  	acm->clocal = ((termios->c_cflag & CLOCAL) != 0);
> >  
> > -	if (!newline.dwDTERate) {
> > +	if (C_BAUD(tty) == B0) {
> >  		newline.dwDTERate = acm->line.dwDTERate;
> >  		newctrl &= ~ACM_CTRL_DTR;
> > -	} else
> > +	} else if (termios_old && (termios_old->c_cflag & CBAUD) == B0) {
> >  		newctrl |=  ACM_CTRL_DTR;
> > +	}
> >  
> >  	if (newctrl != acm->ctrlout)
> >  		acm_set_control(acm, acm->ctrlout = newctrl);
> 
> This should go to older kernels as well, right?

Yes, if you want.

It's fixing handling of B0, but I doubt many people care (hence the
missing stable tag). Note that set_termios is currently not called
during open() (but Jim's patch will be relying on this one).

Johan
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