linux-kernel - Re: [PATCH 1/2] pinctrl: samsung: fix suspend/resume functionality

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Date:	Fri, 17 May 2013 00:08:34 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Kukjin Kim <kgene.kim@...sung.com>,
	Olof Johansson <olof@...om.net>,
	Stephen Warren <swarren@...dotorg.org>,
	Thomas Abraham <thomas.abraham@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Prathyush K <prathyush.k@...sung.com>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Heiko Stübner <heiko@...ech.de>
Subject: Re: [PATCH 1/2] pinctrl: samsung: fix suspend/resume functionality

On Thursday 16 of May 2013 14:51:53 Doug Anderson wrote:
> Tomasz,
> 
> On Thu, May 16, 2013 at 2:27 PM, Tomasz Figa <tomasz.figa@...il.com> 
wrote:
> > OK. I will be fine to go with your patches, after addressing the
> > comments. In the end it's good that you posted them, as reviewing
> > them allowed me to find even better ways of doing some things than I
> > had in mine ;) .
> Yes.  I often find that the best way to review code is to think about
> how I would implement it myself.  Certainly I think we've ended up
> with something better / less buggy this way.  ;)
> 
> > How all of this works is basically a good question. I couldn't find
> > any
> > mention about pins switching from power down to normal mode in the
> > documentation, but maybe there is a small side note somewhere, which I
> > could miss.
> > 
> > On S3C6410, for example, there are two modes. State is switched to
> > power down mode automatically, but can be switched out either
> > automatically on wake-up (exact timing is unknown to me) or by
> > clearing a special bit, depending on value of other special bit.
> > 
> > IMHO this is rather important, so we should find out how it work on
> > other SoCs and make the code account for it.
> 
> Agreed that it's important.  ...but it's also good not to have tons of
> complexity when it's not needed.  It sounds like S3C6410 could be
> handled OK by just using the special bits and waiting to take things
> out of power down mode.
> 
> ...thinking about it, all SoCs that have power down modes (which you
> _must_ have if your pinctrl state is lost across a low power) would be
> slightly broken if they didn't have a bit to switch out of power down
> mode.  Otherwise you're asking for at least some type of glitch
> because you'll end up in the default state of pins for a little while
> during resume.
> 
> That's not to say that there aren't broken SoCs out there and it's
> entirely possible that people even designed systems around them
> (knowing that the default state of each pin after wakeup is not
> harmful to whatever is connected to that pin).  If there are any cases
> like this then they would need the special code like my V1 patch had.
> Do you know of any SoCs like this that we need to support on kernel
> 3.10 and higher?

Hmm, I just checked documentation of S3C2440 and S3C2416 they seem to 
retain GPIO settings completely in sleep mode. This would mean that they 
don't require any suspend/resume support in pinctrl driver. Heiko, can you 
confirm this?

Best regards,
Tomasz

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