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

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Message-ID: <501A4669.9090707@nvidia.com>
Date:	Thu, 2 Aug 2012 18:20:41 +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 05:45:41 PM JST, Thierry Reding wrote:
> * PGP Signed by an unknown key
>
> On Thu, Aug 02, 2012 at 05:27:44PM +0900, Alex Courbot wrote:
>> On Thu 02 Aug 2012 05:21:57 PM JST, Thierry Reding wrote:
>>>> Old 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?
>
> Yes, I think that's exactly what will happen.

Probably not worth to try this then?

Alex.
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