linux-kernel - Re: [PATCH 4/4] serial: core: Mask mctrl with TIOCM_RTS too if rs485 on and RTS_AFTER

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Date:   Wed, 6 Jun 2018 14:07:45 +0200
From:   Giulio Benetti <giulio.benetti@...ronovasrl.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     matwey.kornilov@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Matthias Brugger <mbrugger@...e.com>,
        Kees Cook <keescook@...omium.org>, Sean Young <sean@...s.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] serial: core: Mask mctrl with TIOCM_RTS too if rs485
 on and RTS_AFTER_SEND set.

Il 06/06/2018 14:03, Andy Shevchenko ha scritto:
> On Wed, 2018-06-06 at 11:49 +0200, Giulio Benetti wrote:
>> If rs485 is enabled and RTS_AFTER_SEND is set on startup need to keep
>> TIOCM_RTS asserted to keep rs485 transceiver in RX when idle.
>>
>> Check if rs485 is on and RTS_AFTER_SEND is set and mask port->mctrl
>> with
>> TIOCM_RTS too and not only TIOCM_DTR.
>>
> 
> This one feels wrong to be in serial_core.c. Perhaps in 8250/8250*.c.

I've tried to avoid modifying serial_core.c but if it masks mctrl only 
with TIOCM_DTR, it forces RTS unasserted.
Another way could be:
If rs485 ON and RTS_AFTER_SEND set, then ignore RTS driving in 
8250_set_mctrl, would it make sense?

Thanks

-- 
Giulio Benetti
CTO

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