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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Boris,

On Monday 21 July 2014 15:43:13 Boris BREZILLON wrote:
> On Mon, 21 Jul 2014 15:30:35 +0200 Thierry Reding wrote:
> > On Mon, Jul 21, 2014 at 03:22:05PM +0200, Laurent Pinchart wrote:
> >> On Monday 21 July 2014 14:55:23 Thierry Reding wrote:
> >>> On Mon, Jul 21, 2014 at 02:34:28PM +0200, Boris BREZILLON wrote:
> >>>> On Mon, 21 Jul 2014 14:16:42 +0200 Laurent Pinchart wrote:
> >>>>> On Monday 21 July 2014 14:12:47 Thierry Reding wrote:
> >>>>>> On Mon, Jul 21, 2014 at 11:57:37AM +0200, Boris BREZILLON wrote:
> >>
> >> [snip]
> >> 
> >>>>>>> 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?
> >>>>> 
> >>>>> We do if we want to replace the color_formats and bpc fields.
> >>>> 
> >>>> Yes, that's what I was about to answer :-).
> >>> 
> >>> Maybe we don't need to replace color_formats and bpc field
> >>> immediately. That could be done in a follow-up patch.
> >> 
> >> We don't need to replace them right now, but we should at least agree on
> >> how to replace them. Introducing a new field that would need to be
> >> replaced in the near future when removing color_formats and bpc would
> >> be a waste of time.
> >
> > Sure. One of the problems I see with replacing color_formats and bpc
> > with the above is that some of the bits within color_formats are set
> > when the EDID is parsed. That implies that if they are replaced with
> > an array of formats, the array would need to be reallocated during EDID
> > parsing. That sounds like ugliness.
> > 
> > But if you can find a nice way to make it work that'd be great.
> 
> How about using a list instead of an array ?
> This way we can add elements to this list when parsing the EDID.
> 
> Or we can just define a maximum size for the bus_formats array when
> retrieving this info from EDID. If I'm correct we have at most 18 bus
> formats:
>  - 3 color formats:
>    * RGB 4:4:4
>    * YCbCr 4:4:4
>    * YCbCr 4:4:2
>  - 6 color depths: 6, 8, 10, 12, 14 and 16 bits per color

bpc isn't a bitmask, so EDID supports up to three formats only.

The color_formats field is computed in the drm_add_display_info() function. 
You could easily turn it into a local variable and allocate and fill the 
formats array at the end of the function.

-- 
Regards,

Laurent Pinchart