Re: [RESEND PATCH v3 06/11] drm: add DT bindings documentation for atmel-hlcdc-dc driver

[Thierry Reding <thierry.reding@gmail.com>]

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On Mon, Jul 21, 2014 at 11:57:37AM +0200, Boris BREZILLON wrote:
> On Mon, 21 Jul 2014 11:32:55 +0200
> Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote:
> 
> > Hi Boris,
> > 
> > On Monday 21 July 2014 11:24:38 Boris BREZILLON wrote:
> > > On Mon, 21 Jul 2014 10:59:12 +0200 Thierry Reding wrote:
> > > > On Fri, Jul 18, 2014 at 05:43:34PM +0200, Boris BREZILLON wrote:
> > > > [...]
> > > > 
> > > >>>>>>> + - 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.
> > 
> > I think it is, but just to make sure I understand you correctly, could you 
> > just show how the drm_display_info structure would look like ?
> > 
> 
> The new drm_display_info structure should look like this [2] (except
> that color_formats and bpc have not be removed yet), and [1] is just
> here to show how the video_bus_format enum would look like.
> 
> [1] http://code.bulix.org/rfd0yx-86557
> [2] http://code.bulix.org/7n03b4-86556

Quoting from your paste:

	+   const enum video_bus_format *bus_formats;
	+   int nbus_formats;

Do we really need more than one?

Thierry

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