On Mon, 21 Jul 2014 10:59:12 +0200
Thierry Reding [off-list ref] wrote:

On Fri, Jul 18, 2014 at 05:43:34PM +0200, Boris BREZILLON wrote:
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+ - atmel,panel: Should contain a phandle with 2 parameters.
+   The first cell is a phandle to a DRM panel device
+   The second cell encodes the RGB mode, which can take the following values:
+   * 0: RGB444
+   * 1: RGB565
+   * 2: RGB666
+   * 3: RGB888

These are properties of the panel and should be obtained from the panel
directly rather than an additional cell in this specifier.

Okay.
What's the preferred way of doing this ?
What about defining an rgb-mode property in the panel node.

There's .bpc in struct drm_display_info, I suspect that it could be used
for this. Alternatively, maybe we could extend the list of color formats
that go into drm_display_info.color_formats? RGB444 is already covered.

I forgot to ask about bpc meaning. If, as I think, it means "bits per
color" then it cannot be used to encode RGB565 where green color is
encoded on 6 bits and red and blue are encoded on 5 bits. 

Yes, I agree that bps is not a good fit for what you need here.

Okay, then I think we can replace bpc and color_formats by a bus_formats
table containing all supported formats, and use an enum (something
similar to v4l2_mbus_pixelcode defined in v4l2-mediabus.h [1]) to list
the available formats.

As this implies quite a few changes in crtc core and some drm drivers
(nouveau, i915 and radeon), I'd like to be sure this is what both of you
had in mind.

Best Regards,

Boris

[1]http://lxr.free-electrons.com/source/include/uapi/linux/v4l2-mediabus.h#L37

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com