linux-kernel - Re: [PATCHv9 1/3] Runtime Interpreted Power Sequences

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Message-ID: <CACxGe6tLq7LAb_YwvJVnccJEJNEwKt6heEZER3L7tP1g1WnbXg@mail.gmail.com>
Date:	Thu, 22 Nov 2012 13:01:47 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Tomi Valkeinen <tomi.valkeinen@...com>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Stephen Warren <swarren@...dia.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Mark Zhang <markz@...dia.com>,
	Rob Herring <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv9 1/3] Runtime Interpreted Power Sequences

On Wed, Nov 21, 2012 at 10:00 AM, Alex Courbot <acourbot@...dia.com> wrote:
> On Wednesday 21 November 2012 16:48:45 Tomi Valkeinen wrote:
>> If the power-off sequence disables a regulator that was supposed to be
>> enabled by the power-on sequence (but wasn't enabled because of an
>> error), the regulator_disable is still called when the driver runs the
>> power-off sequence, isn't it? Regulator enables and disables are ref
>> counted, and the enables should match the disables.
>
> And there collapses my theory.
>
>> > Failures might be better handled if sequences have some "recovery policy"
>> > about what to do when they fail, as mentioned in the link above. As you
>> > pointed out, the driver might not always know enough about the resources
>> > involved to do the right thing.
>>
>> Yes, I think such recovery policy would be needed.
>
> Indeed, from your last paragraph this makes even more sense now.
>
> Oh, and I noticed I forgot to reply to this:
>
>> This I didn't understand. Doesn't "<&pwm 2 xyz>" point to a single
>> device, no matter where and how many times it's used?
>
> That's true - however when dereferencing the phandle, the underlying framework
> will try to acquire the PWM, which will result in failure if the same resource
> is referenced several times.
>
> One could compare the phandles to avoid this, but in your example you must
> know that for PWMs the "xyz" part is not relevant for comparison.
>
> This makes referencing of resources by name much easier to implement and more
> elegant with respect to frameworks leveraging.

I would rather (at least for how the DT bindings settle out) see the
design separate the resource references from the sequence. ie. Declare
which resources are used by a device's sequences all in one place and
have the commands index into that.

g.
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