linux-kernel - Re: [RFC PATCH] mmc: Enable wakeup

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Date:	Wed, 26 Jun 2013 22:57:13 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Zoran Markovic <zoran.markovic@...aro.org>
Cc:	Colin Cross <ccross@...roid.com>,
	lkml <linux-kernel@...r.kernel.org>, linux-mmc@...r.kernel.org,
	San Mehat <san@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	Chris Ball <cjb@...top.org>,
	Johan Rudholm <johan.rudholm@...ricsson.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Konstantin Dorfman <kdorfman@...eaurora.org>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] mmc: Enable wakeup_sources for mmc core

On 24 June 2013 21:58, Zoran Markovic <zoran.markovic@...aro.org> wrote:
>>> This patch is ported from the Android common tree, so you've probably
>>> been using it.
>>
>> We removed more or less all Android code in the mmc subsystem, since
>> it just didn't work. :-)
>>
>> The "deferred resume" was very useful though, so after some rework we
>> kept it and could then improve the system resume time significantly.
>
> For what it's worth, I fixed one bug I noticed in the Android kernel:
> if a system has a non-removable MMC device, a suspend/resume cycle on
> this device would hold a wake lock forever. This was a visible issue
> on the panda board I am using.
>
> If there are doubts on whether or not the system should stay awake
> during a MMC mount, we have the option to make the calls to
> wakeup_source_register/unregister configurable. Skipping these calls
> would leave the .ws field NULL, in which case
> __pm_stay_awake/__pm_relax/__pm_wakeup_event would do nothing.

Even if we make this feature configurable, I can't see any host driver
that would benefit from it as of today. The reason is simply that host
drivers do not configure it's card detect irq as a wakeup irq. Myself
is also having quite hard to see the benefit of doing that, but I
don't know all the use cases.

Let's see if we can get someone else to provide input...

>
> Thoughts?
>
> - Zoran


Kind regards
Ulf Hansson
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