linux-kernel - Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

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Date:	Fri, 3 Aug 2012 10:15:46 +0900
From:	Alex Courbot <acourbot@...dia.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Stephen Warren <swarren@...dia.com>,
	Simon Glass <sjg@...omium.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.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>,
	Thierry Reding <thierry.reding@...onic-design.de>
Subject: Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

On Fri 03 Aug 2012 03:11:12 AM JST, Mark Brown wrote:
> On Thu, Aug 02, 2012 at 10:21:57AM +0200, Thierry Reding wrote:
>> On Thu, Aug 02, 2012 at 05:00:13PM +0900, Alex Courbot wrote:
>
>>> The problem is, how do we turn these phandles into the resource of
>>> interest. The type of the resource can be infered by the name of the
>>> property. The hard part is resolving the resource from the phandle -
>>> it seems like the API just does not allow to do this. GPIO has
>>> of_get_named_gpio, but AFAIK there are no equivalent for regulator
>>> consumer and PWM: the only way to use the DT with them is through
>>> get_regulator and get_pwm which work at the device level.
>
>>> Or is there a way that I overlooked?
>
>> No, you are right. Perhaps we should add exported functions that do the
>> equivalent of of_pwm_request() or the regulator_dev_lookup() and
>> of_get_regulator() pair.
>
> I missed some of the earlier bits of the thread here but why can't we do
> device based lookups?

That is because the phandles would not be properties of the device node 
but rather of its sub-nodes:

backlight {
     compatible = "pwm-backlight";
     ...
     power-on-sequence {
         step@0 {
             regulator = <&backlight_reg>;
             enable;
         };


So here simply using regulator_get on the backlight device would not work.

Alex.
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