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

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Message-ID: <4316169.5QXVzv7peZ@percival>
Date:	Wed, 21 Nov 2012 10:56:36 +0900
From:	Alex Courbot <acourbot@...dia.com>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
CC:	Anton Vorontsov <cbouatmailru@...il.com>,
	Stephen Warren <swarren@...dia.com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Mark Zhang <markz@...dia.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [PATCHv9 1/3] Runtime Interpreted Power Sequences

Hi Tomi,

On Tuesday 20 November 2012 22:48:18 Tomi Valkeinen wrote:
> I guess there's a reason, but the above looks a bit inconsistent. For
> gpio you define the gpio resource inside the step. For power and pwm the
> resource is defined before the steps. Why wouldn't "pwm = <&pwm 2
> 5000000>;" work in step2?

That's mostly a framework issue. Most frameworks do not export a function that 
allow to dereference a phandle - they expect resources to be declared right 
under the device node and accessed by name through foo_get(device, name). So 
using phandles in power sequences would require to export these additional 
functions and also opens the door to some inconsistencies - for instance, your 
PWM phandle could be referenced a second time in the sequence with a different 
period - how do you know that these are actually referring the same PWM 
device?

> > +When a power sequence is run, its steps is executed one after the other
> > until +one step fails or the end of the sequence is reached.
> 
> The document doesn't give any hint of what the driver should do if
> running the power sequence fails. Run the "opposite" power sequence?
> Will that work for all resources? I'm mainly thinking of a case where
> each enable of the resource should be matched by a disable, i.e. you
> can't call disable if no enable was called.

We discussed that issue already (around v5 I think) and the conclusion was 
that it should be up to the driver. When we simply enable/disable resources it 
is easy to revert, but in the future non-boolean properties will likely be 
introduced, and these cannot easily be reverted. Moreover some drivers might 
have more complex recovery needs. This deserves more discussion I think, as 
I'd like to have some "generic" recovery mechanism that covers most of the 
cases.

Alex.

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