linux-kernel - Re: [PATCH v4 1/3] Runtime Interpreted Power Sequences

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Message-ID: <1345535069.4085.7.camel@deskari>
Date:	Tue, 21 Aug 2012 10:44:29 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
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 1/3] Runtime Interpreted Power Sequences

Hi,

On Thu, 2012-08-16 at 15:08 +0900, Alexandre Courbot wrote:

> +Problem
> +-------
> +One very common board-dependent code is the out-of-driver code that is used to
> +turn a device on or off. For instance, SoC boards very commonly use a GPIO
> +(abstracted to a regulator or not) to control the power supply of a backlight,
> +disabling it when the backlight is not used in order to save power. The GPIO
> +that should be used, however, as well as the exact power sequence that may
> +also involve other resources, is board-dependent and thus unknown of the driver.
> +
> +This was previously addressed by having hooks in the device's platform data that
> +are called whenever the state of the device might reflect a power change. This
> +approach, however, introduces board-dependant code into the kernel and is not
> +compatible with the device tree.

I've been having the same problems on OMAP display related code, but the
problem has always been fixable by just having the driver to use a
common framework to do the job (a framework which may not have existed
at the time). The problems have never been board specific in the end,
but device specific.

Can you describe your particular HW problem a bit more? In the backlight
case, what exactly requires the delays and the sequence you show in the
example to enable/disable the backlight?

 Tomi


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