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From:   "Matwey V. Kornilov" <matwey.kornilov@gmail.com>
Date:   Wed, 6 Jun 2018 21:55:22 +0300
Message-ID: <CAJs94EZx2ZdEL14SCEBomEfXLRPN4FfOp4yE44kfpnE+5+Ze-g@mail.gmail.com>
Subject: Re: [PATCH 1/4] serial: 8250: Copy em485 from port to real port.
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Giulio Benetti <giulio.benetti@micronovasrl.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Matthias Brugger <mbrugger@suse.com>,
        Kees Cook <keescook@chromium.org>,
        Allen Pais <allen.lkml@gmail.com>, Sean Young <sean@mess.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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2018-06-06 16:11 GMT+03:00 Andy Shevchenko <andriy.shevchenko@linux.intel.com>:
> On Wed, 2018-06-06 at 14:15 +0200, Giulio Benetti wrote:
>> Il 06/06/2018 13:56, Andy Shevchenko ha scritto:
>> > On Wed, 2018-06-06 at 11:49 +0200, Giulio Benetti wrote:
>> > > em485 gets lost during
>> > >
>> > > Copy em485 to final uart port.
>> > >
>> >
>> > Is it needed at all?
>> >
>> > The individual driver decides either to use software emulation (and
>> > calls explicitly serial8250_em485_init() for that) or do HW assisted
>> > stuff.
>>
>> In 8250_dw.c, during probe(), I need to call dw8250_rs485_config()
>> against local struct uart_8250_port uart = {};
>> Inside serial8250_register_8250_port() not all uart fields are
>> copied(em485 too).
>> So after probe, em485 is NULL.
>>
>> Another way could be to call dw8250_rs485_config() against real uart
>> port, after calling serial8250_register_8250_port(),
>> would it make sense?
>
> Look at OMAP case closely. They have a callback to configure RS485 which
> is called in uart_set_rs485_config()  which is called whenever user
> space does TIOCGRS485 IOCTL.
>
> So, it's completely driven by user space which makes sense by my
> opinion.

AFAIU, Giulio wants to add support for rs485-enabled-at-boot-time
device tree option (see bindings/serial/rs485.txt for reference).
I suppose it is only important for use-case when rs485 used as slave
(peripheral role).

>
> --
> Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Intel Finland Oy


-- 
With best regards,
Matwey V. Kornilov