Re: [PATCH 1/4] serial: 8250: Copy em485 from port to real port.

From: Giulio Benetti <giulio.benetti@micronovasrl.com>
To: "Matwey V. Kornilov" <matwey.kornilov@gmail.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: 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>
Subject: Re: [PATCH 1/4] serial: 8250: Copy em485 from port to real port.
Date: Wed, 6 Jun 2018 21:15:15 +0200	[thread overview]
Message-ID: <d3c4e356-2c04-731f-a665-a445a6bf68af@micronovasrl.com> (raw)
In-Reply-To: <CAJs94EZx2ZdEL14SCEBomEfXLRPN4FfOp4yE44kfpnE+5+Ze-g@mail.gmail.com>

Il 06/06/2018 20:55, Matwey V. Kornilov ha scritto:
> 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).

Yes, I want to add support for "rs485-enabled-at-boot-time" property,
maybe I had to write better commit log and a cover letter. Sorry.

> I suppose it is only important for use-case when rs485 used as slave
> (peripheral role).

It's important also for master, because RTS, if RTS_AFTER_SEND is set, 
remains not asserted(trasnmission) until userspace opens that serial port.

Sorry again for not explaining myself well.

-- 
Giulio Benetti
CTO

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