linux-kernel - Re: [PATCH 6/8] serial: 8250: Copy mctrl when register port.

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Date:   Wed, 6 Jun 2018 16:44:13 +0200
From:   Giulio Benetti <giulio.benetti@...ronovasrl.com>
To:     Aaron Sierra <asierra@...-inc.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Matthias Brugger <mbrugger@...e.com>,
        Allen Pais <allen.lkml@...il.com>, Sean Young <sean@...s.org>,
        Ed Blake <ed.blake@...drel.com>,
        Stefan Potyra <Stefan.Potyra@...ktrobit.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Joshua Scott <joshua.scott@...iedtelesis.co.nz>,
        Vignesh R <vigneshr@...com>,
        Rolf Evers-Fischer <rolf.evers.fischer@...iv.com>,
        Rafael Gago <rafael.gago@...il.com>,
        Joel Stanley <joel@....id.au>,
        Sean Wang <sean.wang@...iatek.com>,
        linux-serial <linux-serial@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/8] serial: 8250: Copy mctrl when register port.

Hi Aaron,

Il 06/06/2018 16:31, Aaron Sierra ha scritto:
> ----- Original Message -----
>> From: "Giulio Benetti" <giulio.benetti@...ronovasrl.com>
>> Sent: Friday, June 1, 2018 7:40:19 AM
> 
>> RS485 can modify mctrl on startup, especially when RTS_AFTER_SEND is on
>> TIOCM_RTS is set, then need to keep it set when registering port.
>>
>> Copy mctrl to new port too.
>>
>> Signed-off-by: Giulio Benetti <giulio.benetti@...ronovasrl.com>
>> ---
>> drivers/tty/serial/8250/8250_core.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/tty/serial/8250/8250_core.c
>> b/drivers/tty/serial/8250/8250_core.c
>> index c8c2b260c681..c8e62fbd6570 100644
>> --- a/drivers/tty/serial/8250/8250_core.c
>> +++ b/drivers/tty/serial/8250/8250_core.c
>> @@ -993,6 +993,7 @@ int serial8250_register_8250_port(struct uart_8250_port *up)
>> 		uart->port.unthrottle	= up->port.unthrottle;
>> 		uart->port.rs485_config	= up->port.rs485_config;
>> 		uart->port.rs485	= up->port.rs485;
>> +		uart->port.mctrl	= up->port.mctrl;
> 
> Hi Guilio,
> 
> I ran into this same thing about six months ago, but I was able to
> accomplish what I needed by assigning a set_mctrl() function in my
> port definition. Perhaps that would be enough for your case, too?

Thanks for pointing me.
But wouldn't it be better copying mctrl?
In any case, serial8250_register_8250_port() will call:
- uart_add_one_port()
- uart_configure_port()
- port->ops->set_mctrl(port, mctrl);

So it would be a double call IMHO.
Are there any drawbacks on doing what I'm saying?
Maybe I'm missing something.

> You should see a little lower in this file that set_mctrl is copied
> to the new port. > -Aaron
> 
>> 		uart->dma		= up->dma;
>> 		uart->em485		= up->em485;
>>
>> --
>> 2.17.0

-- 
Giulio Benetti
CTO

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