[PATCH 2/2] drm: add an fb creation ioctl that takes a pixel format v4

[Rob Clark]

On Mon, Nov 14, 2011 at 3:16 PM, Ville Syrjälä
<ville.syrjala at linux.intel.com> wrote:
> On Mon, Nov 14, 2011 at 12:21:55PM -0800, Jesse Barnes wrote:
>> +#define fourcc_code(a,b,c,d) ((u32)(a) | ((u32)(b) << 8) | \
>> +                           ((u32)(c) << 16) | ((u32)(d) << 24))
>> +
>> +/* RGB codes */
>> +#define DRM_FOURCC_RGB332 fourcc_code('R','G','B','1')
>> +#define DRM_FOURCC_RGB555 fourcc_code('R','G','B','O')
>> +#define DRM_FOURCC_RGB565 fourcc_code('R','G','B','P')
>> +#define DRM_FOURCC_RGB24  fourcc_code('R','G','B','3')
>> +#define DRM_FOURCC_RGB32  fourcc_code('R','G','B','4')
>> +
>> +#define DRM_FOURCC_BGR24  fourcc_code('B','G','R','3')
>> +#define DRM_FOURCC_BGR32  fourcc_code('B','G','R','4')
>
> I'm confused by these. The code suggests RGB/BGR24 are in fact 32bpp
> formats, so why do we need the RGB/BGR32 variants? If the difference
> is in the alpha channel, I'd like to document that fact in the name.
>
> Could we call them ARGB8888, XRGB8888, XRGB1555 etc.?
>
> Also the channel and byte order should be documented clearly.
>
> And one other thing. I probably wouldn't call these fourccs
> since they don't actually match the official fourccs. Not that
> there is anything sensible defined for RGB formats in the
> official list anyway. In fact, I'm not sure what we gain by
> cooking our own fourccs when we know most of them won't match
> the official list. AFAICS a simple running number would do
> just as well as the format identifier.

I expect that v4l just made up their own fourcc values for some of the
RGB formats..  which isn't a horrible idea, and seems worthwhile to be
aligned with names/values that v4l already picked.  At least then we
don't have two different sets of more or less arbitrary rgb fourcc
names..

BR,
-R

> --
> Ville Syrjälä
> Intel OTC
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