linux-kernel - Re: SDHCI long sleep with interrupts off

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Date:	Thu, 17 Dec 2015 15:54:54 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	David Jander <david@...tonic.nl>
Cc:	Lucas Stach <l.stach@...gutronix.de>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	Pierre Ossman <pierre@...man.eu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: SDHCI long sleep with interrupts off

[...]

>> If/when you decide to fix this issue. Please keep in mind the following
>> things.
>>
>> - Try to convert the SDHCI into a pure library. No more quirks or callbacks.
>> - I assume we can simplify lots of code if we convert SDHCI into using
>> a threaded IRQ in favour of the tasklet.
>>
>> Any patches that moves SDHCI into this direction will be greatly appreciated!
>
> Ok, this sounds like a good way to go. Unfortunately it also sounds like a
> major endeavor, for which good knowledge of the SDHCI standard is necessary.
> This knowledge is based on documentation that is not openly available without
> cost AFAIK. This probably also explains why there hasn't been a real fix ever.
> On top of that, the whole sdhci code is unmaintained currently as it seems.
> I was studying the code a bit more, and I now understand that I am not even
> close to having the experience and standards-knowledge it takes to pull this
> off reliably. I guess the one who takes on this task may as well become
> official maintainer afterwards...

You are right, a maintainer is needed for sdhci.

Also, I am a bit surprised that none have stepped up, especially since
it's indeed being *very* widely used.

> OTOH, we pretty much depend on this driver now, since all of our new i.MX6/7
> boards have eMMC flash. We also use the flexcan peripheral on all designs,
> which is specially sensible to these latency spikes, so we will have to do
> something on the long run.... we cannot live forever with disabled PM ;-)
>

Unfortunate, PM is only one of the problems.

The code is in general fragile. We have have kind of reached the
point, when I apply changes that fixes one issue it may cause another.

Kind regards
Uffe
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