Date:	Wed, 21 Nov 2012 10:13:47 +0200
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Alex Courbot <acourbot@...dia.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

On 2012-11-21 03:56, Alex Courbot wrote:
> 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 

Right, I expected something like that.

> 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?

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?

>>> +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.

Ok. I'll need to dig up the conversation. Did you consider any examples
of how some driver could handle the error cases?

What I'm worried about is that, as far as I understand, the power
sequence is kinda like black box to the driver. The driver just does
"power-up", without knowing what really goes on in there.

And if it doesn't know what goes on in there, nor what's in "power-down"
sequence, how can it do anything when an error happens? The only option
I see is that the driver doesn't do anything, which will leave some
resources enabled, or it can run the power-down sequence, which may or
may not work.

 Tomi



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