Re: [RFC/PATCH] drm: Add XRGB8626262 (RGB 6:6:6) pixel format

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

Hi Ville,

On Wednesday 27 March 2013 13:06:20 Ville Syrjälä wrote:
> On Wed, Mar 27, 2013 at 10:19:29AM +0100, Laurent Pinchart wrote:
> > This format is an odd beast, implemented by Renesas R-Car hardware. It
> > stores RGB 6:6:6 pixels in 32 bits as
> > 
> > [31:0] x:R:x:G:x:B:x 8:6:2:6:2:6:2 little endian
> > 
> > Signed-off-by: Laurent Pinchart
> > <laurent.pinchart+renesas@ideasonboard.com>
> > ---
> > 
> > Hello,
> > 
> > I came across this weird format on a Renesas SoC display controller. This
> > is essentially XRGB8888 with the two low order bits of each component
> > ignored by the hardware.
> 
> It sounds like it's no different than shoveling XRGB8888 down a 6bpc
> pipe w/o dithering.
> 
> Could we just pretend it's XRGB8888, or can the low order bits have
> some special meaning which would require treating them as special?

The hardware supports both XRGB8888 and the weird RGB 666 format, so I need a 
new 4CC if I want to expose both to userspace.

If the display uses a 6bpc pipe XRGB888 and RGB 666 should be identical. If 
the display uses a 8bpc pipe then the two formats will be different. What 
remains to be found is a use case where an application would fill the two low 
order bits with a non-zero value and expect the hardware to ignore them.

-- 
Regards,

Laurent Pinchart