linux-kernel - Re: [PATCH] usb-serial/ftdi

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Message-ID: <20100603122309.GJ2698@buzzloop.caiaq.de>
Date:	Thu, 3 Jun 2010 14:23:09 +0200
From:	Daniel Mack <daniel@...aq.de>
To:	Alan Cox <alan@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Johan Hovold <jhovold@...il.com>, linux-usb@...r.kernel.org
Subject: Re: [PATCH] usb-serial/ftdi_sio: fix DTR/RTS line modes

On Thu, Jun 03, 2010 at 12:32:25PM +0100, Alan Cox wrote:
> On Thu,  3 Jun 2010 13:55:02 +0200
> Daniel Mack <daniel@...aq.de> wrote:
> 
> > Call set_mctrl() and clear_mctrl() according to the flow control mode
> > selected. This makes serial communication for FT232 connected devices
> > work when CRTSCTS is not set.
> > 
> > This fixes a regression introduced by 4175f3e31 ("tty_port: If we are
> > opened non blocking we still need to raise the carrier"). This patch
> > calls the low-level driver's dtr_rts() function which consequently
> > sets TIOCM_DTR | TIOCM_RTS. A later call to set_termios() without
> > CRTSCTS in cflags, however, does not reset these bits, and so data is
> > not actually sent out on the serial wire.
> 
> If you've got hardware the other end expecting RTS/CTS signals you
> really ought to set CRTSCTS. 

I know. It is, however, a regression in my case, and there might be
other cases where RTS/CTS aren't connected at all. The core of the
problem is that the driver sets hardware flow control, even though the
userspace asked for not doing that.

> However you patch makes complete sense in
> terms of which way it is best to end up.

And it shouldn't break anything I'd say.

Thanks,
Daniel

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