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

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Date:	Mon, 30 Jul 2012 16:26:28 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Rob Herring <robherring2@...il.com>
CC:	Alexandre Courbot <acourbot@...dia.com>,
	Stephen Warren <swarren@...dia.com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Simon Glass <sjg@...omium.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arnd Bergmann <arnd@...db.de>, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

On 07/30/2012 09:44 AM, Rob Herring wrote:
> On 07/27/2012 07:05 AM, Alexandre Courbot wrote:
>> Some device drivers (panel backlights especially) need to follow precise
>> sequences for powering on and off, involving gpios, regulators, PWMs
>> with a precise powering order and delays to respect between each steps.
>> These sequences are board-specific, and do not belong to a particular
>> driver - therefore they have been performed by board-specific hook
>> functions to far.
>>
>> With the advent of the device tree and of ARM kernels that are not
>> board-tied, we cannot rely on these board-specific hooks anymore but
>> need a way to implement these sequences in a portable manner. This patch
>> introduces a simple interpreter that can execute such power sequences
>> encoded either as platform data or within the device tree.
>>
> 
> Why not? We'll always have some amount of board code. The key is to
> limit parts that are just data. I'm not sure this is something that
> should be in devicetree.
> 
> Perhaps what is needed is a better way to hook into the driver like
> notifiers?

I would answer that by asking the reverse question - why should we have
to put some data in DT, and some data into board files still?

I'd certainly argue that the sequence of which GPIOs/regulators/PWMs to
manipulate is just data.

To be honest, if we're going to have to put some parts of a board's
configuration into board files anyway, then the entirety of DT seems
useless; I'd far rather see all the configuration in one cohesive place
than arbitrarily split into two/n different locations - that would make
everything harder to maintain.
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