linux-kernel - Re: [PATCH 0/3] serial: samsung: Fix UART status handling and other fixes

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Message-id: <55F0CD8B.8080403@samsung.com>
Date:	Thu, 10 Sep 2015 09:23:39 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Robert Baldyga <r.baldyga@...sung.com>, gregkh@...uxfoundation.org
Cc:	jslaby@...e.com, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, m.szyprowski@...sung.com
Subject: Re: [PATCH 0/3] serial: samsung: Fix UART status handling and other
 fixes

On 09.09.2015 18:15, Robert Baldyga wrote:
> On 09/09/2015 01:47 AM, Krzysztof Kozlowski wrote:
>> On 08.09.2015 18:38, Robert Baldyga wrote:
>>> Hello,
>>>
>>> This patch set contains three patches: two minor fixes and one quite
>>> important bugfix enabling UART status handling in DMA mode, which was
>>> missing so far. It enables, among others, 'break' contition handling,
>>> which is necessary if we want to use Magic SysRq. So this patch fixes
>>> Magic SysRq handling for serial consoles using UART in DMA mode,
>>
>> Is it even worth using UART for serial console in DMA mode? How many
>> benefits it brings? Anyone measured real data?
>>
>> The patch which enabled DMA for all serial ports on Exynos4 uncovered
>> some issues. That is one benefit... but was it worth it?
> 
> Well, UART in DMA mode should work at least as good as in PIO, so there
> is nothing wrong in having serial console configured in DMA. Sure, it
> rather barely reduces number of interrupts while used as typical serial
> console, but in some cases (eg. using zmodem) it can be more profitable.

That's some reason... and mentioned earlier testing of DMA which
uncovered some interesting issues. :)

> 
> To be honest, I have no strong feeling about that. I've decided to
> utilize new possibility opened by introducing DMA mode in serial driver,
> so I've send patch enabling it for each port on Exynos4. But if it
> turned out to be unneeded I will not insist on it.

I was just thinking loud... I don't have any data neither so let's go
ahead with serial DMA.

Best regards,
Krzysztof
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