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

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Message-ID: <20130130074852.GB17547@avionic-0098.mockup.avionic-design.de>
Date:	Wed, 30 Jan 2013 08:48:52 +0100
From:	Thierry Reding <thierry.reding@...onic-design.de>
To:	Alex Courbot <acourbot@...dia.com>
Cc:	Mark Zhang <nvmarkzhang@...il.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Mark Zhang <markz@...dia.com>,
	"linux-kernel@...r.kernel.org" <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>,
	"gnurou@...il.com" <gnurou@...il.com>
Subject: Re: [RFC 1/4] video: panel: add CLAA101WA01A panel support

On Wed, Jan 30, 2013 at 04:27:11PM +0900, Alex Courbot wrote:
> On 01/30/2013 04:20 PM, Mark Zhang wrote:
[...]
> >>+static int panel_claa101_get_modes(struct display_entity *entity,
> >>+				   const struct videomode **modes)
> >>+{
> >>+	/* TODO get modes from EDID? */
> >
> >Why not move the "nvidia,ddc" from encoder's DT to panel's DT? In that
> >case, you can get EDID here. I know drm has some helpers to fetch EDID
> >but I recall there are some other functions which has no drm
> >dependencies which may be suitable for you.
> 
> I explained this in the cover letter - I'm not sure we want to have
> a dependency on DRM here, as CDF entities could also be connected to
> other subsystems. That's something we need to figure out. But yes,
> ultimately this should be the place where EDID is retrieved.

I already said this in another thread. I think we should only be using
the CDF .get_modes() for static modes that cannot be obtained from EDID.
Thinking about it, I'm not quite sure why EDID would be needed for this
kind of panel anyway. Ventana probably has it because it keeps us from
having to hardcode things, but if we provide drivers for the panel
anyway, we can just as well hard-code the supported mode(s) in those
drivers.

What I'm trying to say is that the existence of EDID is board-specific,
so boards other than Ventana may not have an EDID EEPROM. Or perhaps
this particular display has the EEPROM integrated? Even in that case,
some boards may use this panel and simply not connect the EEPROM to an
I2C controller.

Thierry

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