linux-kernel - Re: [PATCH v4 2/3] pwm_backlight: use power sequences

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Date:	Thu, 16 Aug 2012 12:42:24 -0600
From:	Stephen Warren <swarren@...dotorg.org>
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 2/3] pwm_backlight: use power sequences

On 08/16/2012 12:08 AM, Alexandre Courbot wrote:
> Make use of the power sequences specified in the device tree or platform
> data to control how the backlight is powered on and off.

> +++ b/Documentation/devicetree/bindings/video/backlight/pwm-backlight.txt

>  Required properties:
>    - compatible: "pwm-backlight"
> -  - pwms: OF device-tree PWM specification (see PWM binding[0])
>    - brightness-levels: Array of distinct brightness levels. Typically these
>        are in the range from 0 to 255, but any range starting at 0 will do.
>        The actual brightness level (PWM duty cycle) will be interpolated
> @@ -10,19 +9,72 @@ Required properties:
>        last value in the array represents a 100% duty cycle (brightest).
>    - default-brightness-level: the default brightness level (index into the
>        array defined by the "brightness-levels" property)
> +  - pwms: OF device-tree PWM specification (see PWM binding[0]). Exactly one PWM
> +      must be specified

There's probably no need to move that entry just to change it?

>  Optional properties:
> -  - pwm-names: a list of names for the PWM devices specified in the
> -               "pwms" property (see PWM binding[0])

> +  - *-supply: regulators used within a power sequence
> +  - *-gpio: GPIOs used within a power sequence

I don't think these really warrant mentioning here; such properties are
part of the standard regulator and GPIO bindings, and are required as a
side-effect of a power sequence using a resource of those types, rather
than being something actively defined or needed directly by the
pwm-backlight binding.

> +  - pwm-names: name for the PWM device specified in the "pwms" property (see PWM
> +      binding[0]). Necessary if power sequences are used

> +  - power-on-sequence: Power sequence (see Power sequences[1]) used to bring the
> +      backlight on. This sequence must reference the PWM specified in the pwms
> +      property by its name. It can also reference other resources supported by
> +      the power sequences mechanism
> +  - power-off-sequence: Power sequence (see Power sequences[1]) used to bring
> +      the backlight off. This sequence must reference the PWM specified in the
> +      pwms property by its name. It can also reference other resources supported
> +      by the power sequences mechanism

For these two, I would personally simply say that the pwm-backlight
binding requires that two power sequences named "on" and "off" must
exists, and are to defined according to [1].

>  [0]: Documentation/devicetree/bindings/pwm/pwm.txt
> +[1]: Documentation/devicetree/bindings/power_seq/power_seq.txt
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