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

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Message-ID: <20100603123225.55f544ff@linux.intel.com>
Date:	Thu, 3 Jun 2010 12:32:25 +0100
From:	Alan Cox <alan@...ux.intel.com>
To:	Daniel Mack <daniel@...aq.de>
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,  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. However you patch makes complete sense in
terms of which way it is best to end up.
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