linux-kernel - Re: [RFC][PATCH 0/4] lcd: platform-lcd: Add lcd panel and device tree support

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Message-ID: <CAJuYYwTGWHCpEnE5w8b7mmg_oaFiygQSSey7ra+nR+Q9_Bi_tA@mail.gmail.com>
Date:	Mon, 2 Jan 2012 23:01:54 +0530
From:	Thomas Abraham <thomas.abraham@...aro.org>
To:	Olof Johansson <olof@...om.net>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	rpurdie@...ys.net, linux-samsung-soc@...r.kernel.org,
	grant.likely@...retlab.ca, rob.herring@...xeda.com,
	kgene.kim@...sung.com, jg1.han@...sung.com,
	broonie@...nsource.wolfsonmicro.com, kyungmin.park@...sung.com,
	cbou@...l.ru, kwangwoo.lee@...il.com, augulis.darius@...il.com,
	ben-linux@...ff.org, patches@...aro.org
Subject: Re: [RFC][PATCH 0/4] lcd: platform-lcd: Add lcd panel and device tree support

Hi Olof,

On 2 January 2012 12:18, Olof Johansson <olof@...om.net> wrote:
> Hi,
>
> On Sun, Jan 1, 2012 at 9:54 PM, Thomas Abraham
> <thomas.abraham@...aro.org> wrote:
>> The platform-lcd driver depends on platform-specific callbacks to setup the
>> lcd panel. These callbacks are supplied using driver's platform data. But
>> for adding device tree support for platform-lcd driver, providing such
>> callbacks is not possible (without using auxdata).
>>
>> Since the callbacks are usually lcd panel specific, it is possible to include
>> the lcd panel specific setup and control functionality in the platform-lcd
>> driver itself, thereby eliminating the need for supplying platform specific
>> callbacks to the driver. The platform-lcd driver can include support for
>> multiple lcd panels.
>>
>> This patchset removes the need for platform data for platform-lcd driver and
>> adds support which can be used to implement lcd panel specific functionality
>> in the driver. As an example, the support for Hydis hv070wsa lcd panel is added
>> to the platform-lcd driver which is then used on the Exynos4 based Origen board.
>> This currently breaks build for other users of platform-lcd driver. Those can be
>> fixed if this approach is acceptable.
>
> I think it would be a better idea to provide a generic binding for the
> simple LCD panels that just need one or two power GPIOs to be turned
> on (some tend to need one to activate and one for power control --
> second might in some cases be handled through a regulator I suppose).
> I'm sure there will be exceptions to this; panels that have quirks or
> requirements on various things that will either require an expanded
> binding, or custom probe functions.

A majority of the existing users of the platform-lcd driver are using
a single gpio to enable or disable the display. As you mentioned, a
generic binding can be added for such lcd panels. There are other
implementations that use one or more gpios but requires toggling those
gpios in a panel specific way (usually with some delay). Such
implementations will require custom panel support included in the
platfrom-lcd driver. I will prepare a patch for these cases.

>
> Especially in the case you are providing -- that lcd driver is only
> using a single gpio, and it would be much more valuable to have a
> trivial binding for this that uses shared code for this. Otherwise
> every single simple panel will need to be added over time.

Yes. I agree. It is better to have a common binding and there are many
panels that can use this generic binding. I will make these changes.

Thanks for your review.

Regards,
Thomas.

>
>
> -Olof
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