linux-kernel - Re: [PATCH v4 0/3] Runtime Interpreted Power Sequences

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Date:	Thu, 16 Aug 2012 23:47:34 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	Stephen Warren <swarren@...dia.com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Simon Glass <sjg@...omium.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Anton Vorontsov <cbou@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>,
	Arnd Bergmann <arnd@...db.de>,
	Leela Krishna Amudala <leelakrishna.a@...il.com>,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 0/3] Runtime Interpreted Power Sequences

On Thursday, August 16, 2012, Alexandre Courbot wrote:
> Overdue revision of this new feature, some changes required additional thought
> and rework.
> 
> The most important change is in the way power sequences are expressed in the
> device tree. In order to avoid having to specify #address-cells, #size-cells and
> reg properties, the @ notation in the step names is dropped, and instead a
> fixed, sequential naming is adopted. The type of the resource used by a step is
> decided by the presence of some recognized properties:
> 
> power-on-sequence {
> 	step0 {
> 		regulator = "power";
> 		enable;
> 	};
> 	step1 {
> 		delay = <10000>;
> 	};
> 	step2 {
> 		pwm = "backlight";
> 		enable;
> 	};
> 	...
> 
> To me this looks safe, clear and close to the platform data representation, but
> needs approval from DT experts.
> 
> Resources are still referenced by name instead of having their phandles defined
> directly inside the sequences, as previous discussion came to the conclusion
> that doing so would require controversial changes to the regulator and PWM
> frameworks, and that having the resources declared at the device level was
> making sense logically speaking.
> 
> Other changes/fixes since last revision:
> * Move to drivers/power/ (hope this is ok with the maintainers?)
> * Use microseconds for delay
> * Use devm for PWM resources and remove cleanup function as all resources are
>   devm-managed
> * Remove "-gpio" suffix for GPIO reference in the driver
> * Remove params structure
> * Make power_seq structure private
> * Number of steps in a sequence is explicitly stated instead of resorting to a
>   "stop" sequence step
> * Delays are a step instead of being a step parameter
> * Use flexible member arrays to limit number of memory allocations
> * Add documentation to DT bindings
> 
> There was a lot of feedback on the previous version (thanks!) so if I forgot
> to address some important point, please bring it to my attention again.
> 
> Alexandre Courbot (3):
>   Runtime Interpreted Power Sequences
>   pwm_backlight: use power sequences
>   tegra: add pwm backlight device tree nodes

May I ask that the next version of this patchset be CCed to
linux-pm@...r.kernel.org?

Thanks,
Rafael
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