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

[Boris BREZILLON <boris.brezillon@free-electrons.com>]

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



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