linux-kernel - Re: [PATCH v2 1/2] serial: 8250_early: do not save and restore IER in write callback

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Date:	Thu, 29 Oct 2015 14:21:45 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	linux-serial@...r.kernel.org,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Kevin Cernekee <cernekee@...il.com>,
	Jiri Slaby <jslaby@...e.com>, Rob Herring <robh@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 1/2] serial: 8250_early: do not save and restore IER in
 write callback

2015-10-28 23:36 GMT+09:00 Peter Hurley <peter@...leysoftware.com>:
> On 10/27/2015 11:27 PM, Masahiro Yamada wrote:
>> Hi Peter,
>>
>> 2015-10-27 22:54 GMT+09:00 Peter Hurley <peter@...leysoftware.com>:
>>> Hi Masahiro,
>>>
>>> On 10/24/2015 12:17 AM, Masahiro Yamada wrote:
>>>> The IER has already been masked in early_serial8250_setup(), there is
>>>> no reason to save and restore it every time early_serial8250_write()
>>>> is called.
>>>>
>>>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>>>> ---
>>>>
>>>>  drivers/tty/serial/8250/8250_early.c | 12 ------------
>>>>  1 file changed, 12 deletions(-)
>>>>
>>>> diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
>>>> index 7aff3d8..559b681 100644
>>>> --- a/drivers/tty/serial/8250/8250_early.c
>>>> +++ b/drivers/tty/serial/8250/8250_early.c
>>>> @@ -99,20 +99,8 @@ static void __init early_serial8250_write(struct console *console,
>>>>  {
>>>>       struct earlycon_device *device = console->data;
>>>>       struct uart_port *port = &device->port;
>>>> -     unsigned int ier;
>>>> -
>>>> -     /* Save the IER and disable interrupts preserving the UUE bit */
>>>> -     ier = serial8250_early_in(port, UART_IER);
>>>> -     if (ier)
>>>> -             serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
>>>>
>>>>       uart_console_write(port, s, count, serial_putc);
>>>
>>>
>>>
>>>> -
>>>> -     /* Wait for transmitter to become empty and restore the IER */
>>>> -     wait_for_xmitr(port);
>>>
>>> This wait_for_xmitr() change needs to be in patch 2/2.
>>>
>>
>>
>> Why?
>
> Because if someone reports a regression bisected to this commit,
> we won't know if the regression is because we're not saving/restoring IER
> or because the transmitter is still running.
>

Good point.

I will send v3.
Thanks!



-- 
Best Regards
Masahiro Yamada
--
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