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

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Message-ID: <501A3A00.7070207@nvidia.com>
Date:	Thu, 2 Aug 2012 17:27:44 +0900
From:	Alex Courbot <acourbot@...dia.com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
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>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	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>
Subject: Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

On Thu 02 Aug 2012 05:21:57 PM JST, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Thu, Aug 02, 2012 at 05:00:13PM +0900, Alex Courbot wrote:
>> On 07/31/2012 07:45 AM, Stephen Warren wrote:
>>> Oh I see. That's a little confusing. Why not just reference the relevant
>>> resources directly in each step; something more like:
>>>
>>> 		gpio@1 {
>>> 			action = "enable-gpio";
>>> 			gpio = <&gpio 1 0>;
>>> 		};
>>>
>>> I guess that might make parsing/building a little harder, since you'd
>>> have to detect when you'd already done gpio_request() on a given GPIO
>>> and not repeat it or something like that, but to me this makes the DT a
>>> lot easier to comprehend.
>>
>> I tried to move towards having the phandles directly in the
>> sequences themselves - that reminded me why I did not do that in the
>> first place. Let's say we have a sequence like this (reg property
>> omitted on purpose):
>>
>> 	power-on-sequence {
>> 		step@0 {
>> 			regulator = <&backlight_reg>;
>> 			enable;
>> 		};
>> 		step@1 {
>> 			delay = <10000>;
>> 		};
>> 		step@2 {
>> 			pwm = <&pwm 2 5000000>;
>> 			enable;
>> 		};
>> 		step@3 {
>> 			gpio = <&gpio 28 0>;
>> 			enable;
>> 		};
>> 	};
>>
>> 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.

How would that be looked with respect to "good DT practices"? I can 
somehow understand the wish to restrain DT access to these functions 
that integrate well with current workflows. Aren't we going to be 
frowned upon if we make more low-level functions public?

Alex.
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