linux-kernel - Re: [RFC 1/4] video: panel: add CLAA101WA01A panel support

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Date:	Thu, 31 Jan 2013 13:14:21 +0900
From:	Alexandre Courbot <acourbot@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Thierry Reding <thierry.reding@...onic-design.de>,
	Mark Zhang <markz@...dia.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Alexandre Courbot <gnurou@...il.com>
Subject: Re: [RFC 1/4] video: panel: add CLAA101WA01A panel support

On Thu, Jan 31, 2013 at 5:27 AM, Stephen Warren <swarren@...dotorg.org> wrote:
> So this looks like a reasonable binding to me. The one issue is that
> it's very generic, and if we go this route, we'll probably end up with
> tens or hundreds of identical or extremely similar simple bindings, and
> associated drivers.
>
> We can avoid this instead by defining something like a "simple-lcd"
> binding, and associated driver, that will work for perhaps 90%, 95%,
> 99%, even 100%(?) of panels.

That seems totally doable indeed. Actually the right way to do this
might be by extending the simple DPI panel driver Laurent included in
his patchset.

> Just like the above, but with:
>
> compatible="simple-panel", "chunghwa,claa101wa01a"
>
> instead, and the driver binding to "simple-panel" rather than
> "chunghwa,claa101wa01a".

Just out of curiosity, why don't we rather define

compatible="chunghwa,claa101wa01a", "simple-panel"

in that order? I thought DT compatible strings should go from more to
less specific. The device would still bind to "simple-panel" if no
more specific driver exists.

> The driver can assume that a specific set of supplies (and perhaps
> GPIOs) is always present, and that the /sequence/ of manipulating those
> is fixed. This will avoid the need for anything like the power sequences
> code. If a particular panel doesn't fit those assumptions, including the
> exact sequence of manipulations for each state transition (which should
> be documented in the binding) then it can get a custom driver, this also
> avoiding having to define custom sequences in DT.
>
> Things that might be parameterized/optional:
>
> * Perhaps some GPIOs aren't always present.
> * If some regulators aren't SW-controllable, DT should still provide a
> fixed/dummy regulator so the driver doesn't care.

How about making all regulators and GPIO optional in the driver?

> * Wait times between regulator/GPIO/... manipulation could be specified
> in DT.
> * For panels without EDID, CDF DT bindings can provide the list of
> supported modes, otherwise we assume that the display controller that
> drives the panel has been told how to access the EDID, just like it
> would for an "external" display.

Excellent. Thanks for the feedback.

Alex.
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