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SubjectRe: [PATCH v1 0/3] console, serial8250: Disable PM and DMA ops
On Wed, May 16, 2018 at 1:08 PM, Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
> On 2018-05-15 21:37:18 [+0300], Andy Shevchenko wrote:
>> On Tue, 2018-05-15 at 21:34 +0300, Andy Shevchenko wrote:
>> > Kernel console is sensitive to any kind of complex work needed to
>> > print
>> > out anything on it. One such case is emergency print during Oops.
>> >
>> > This series proposes to disable runtime PM and DMA operations on 8250
>> > serial console.
>> >
>> > More detailed explanation why is provided in patch 2.
>> >
>> > The series has been in our internal trees for years already with no
>> > problems observed.
>>
>> +Cc: Tony.
>>
>> You might have some thoughts / test means for this.
>
> I haven't look at the patches, just your cover letter. Disabling DMA on
> kernel-console should be fine.

Would you mind to give an Ack for it?

> The output is usually short so there
> shouldn't be much benefit from using it.

> I remember Tony wanted runtime-pm on the kernel console, too. And he
> told me explicit how to test it so that it works. Once the UART goes
> into PM (down), the whole IP block can go into power save mode. The
> board can be woken up by sending a character via the UART. The first few
> (incoming / read) characters are lost until the IP block is up again the
> frequency stable. This is known / expected.

Don't consider world the OMAP only. The things more complicated if we
go out of it. Which I tried to explain in the commit message of patch
2.

> In order to achieve the same thing you would have to disable the kernel
> console on that UART. I leave this to Tony.

Precisely the point of the series.


--
With Best Regards,
Andy Shevchenko

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