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

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Message-ID: <20120801071743.GC29673@avionic-0098.adnet.avionic-design.de>
Date:	Wed, 1 Aug 2012 09:17:43 +0200
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	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 Wed, Aug 01, 2012 at 11:50:35AM +0900, Alex Courbot wrote:
> On 07/31/2012 07:19 PM, Thierry Reding wrote:
> >* PGP Signed by an unknown key
> >
> >On Tue, Jul 31, 2012 at 06:51:03PM +0900, Alex Courbot wrote:
> >>I would like to do that actually. The issue is that it did not work
> >>go well with the legacy pwm_backlight behavior: a power sequence
> >>needs to be constructed out of a PWM obtained through
> >>pwm_request(int pwm_id, char *label) and this behavior cannot be
> >>emulated using the new platform data interface (which only works
> >>with pwm_get()). But if I remove this old behavior, then I could
> >>make power_seq opaque. I don't think many drivers are using it. What
> >>do you think?
> >
> >I don't see how that is relevant here, since this power-sequencing code
> >is supposed to be generic and not tied to any specific implementation.
> >Can you explain further?
> >
> >In any case you shouldn't be using pwm_request() in new code.
> 
> Power sequences only rely on pwm_get, and never call pwm_request
> since it is, as you stated, deprecated. However there are still
> boards that use the old pwm_id member of the
> pwm_backlight_platform_data. For these, we must call pwm_request
> from the pwm_backlight driver in order to resolve the PWM (see
> pwm_backlight_legacy_probe of the seconds patch). As the PWM is
> being resolved by the backlight driver, and not within the power
> sequences parser, the resolved data structure must be visible to
> pwm_backlight so it can construct it. There are two ways to solve
> this and keep the power sequences structure private:
> 
> 1) Add a way to resolve a PWM by id using pwm_request in the power
> sequences (we probably should not do that)

No. But I think we don't need that either. If you use power sequences,
then you shouldn't be using the pwm_id member. Both methods should be
exclusive.

> 2) Port the old platform pwm_request code to use pwm_add_table and
> pwm_get instead.

In the long term, every PWM user should move to pwm_add_table() and
pwm_get(), but there are quite a lot of boards that need conversion.

> Do I get points if I do 2)? :)

Yes. =) I have a sample patch for PXA EZX, but as I said, many more
boards need conversion.

Thierry

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