linux-kernel - Re: [PATCH 2/2] ARM: DT: tegra: pinctrl suspend resume hook

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Date:	Thu, 02 May 2013 12:33:31 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Bibek Basu <bbasu@...dia.com>
CC:	Thierry Reding <thierry.reding@...onic-design.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 2/2] ARM: DT: tegra: pinctrl suspend resume hook

On 04/28/2013 07:42 AM, Bibek Basu wrote:
>> -----Original Message-----
>> From: Thierry Reding [mailto:thierry.reding@...onic-design.de]
>> Sent: Saturday, April 27, 2013 1:19 AM
>> To: Bibek Basu
>> Cc: Rafael J. Wysocki; linus.walleij@...aro.org; swarren@...dotorg.org;
>> linux-tegra@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
>> pm@...r.kernel.org
>> Subject: Re: [PATCH 2/2] ARM: DT: tegra: pinctrl suspend resume hook
>>
>> * PGP Signed by an unknown key
>>
>> On Tue, Apr 23, 2013 at 11:39:02PM +0530, Bibek Basu wrote:
>>> Make pinmux as the first node of tegra DT so as to achieve pinctrl as
>>> last device to suspend and first device to resume.
>>
>> I don't think this is a good idea. For one it encodes Linux specific
>> implementation details within the device tree. Furthermore I seem to
>> remember that the device tree makes no guarantees that the order of nodes
>> in the blob is the same as the order in the DTS.
>>
>> That said I don't have a good alternative. Perhaps one solution would be to
>> use suspend_late() and resume_early() for the pinmux driver since they will
>> be called after and before the suspend() and resume() callbacks of all other
>> devices, respectively. Other than that I wasn't able to find anything about
>> forcing a particular order during suspend and resume.
>>
>> Cc'ing Rafael and the linux-pm mailing list, maybe somebody among them
>> knows a proper solution.
>
> Stephen actually suggested me earlier to add dummy pinmux state on all dependent devices node. And that will make sure that dependency of driver prevails.
> I tried that but I was not getting the desired result.
> Can anyone tell me correct syntax for adding dummy state?

I agree with Thierry that this patch is not the correct approach.

A dummy pinctrl state would look something like the following in each
affected device node:

                pinctrl-names = "default";
                pinctrl-0 = <>;

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