On Wednesday, 2017-04-26 07:53:10 +0200, Gerd Hoffmann wrote:
> On Di, 2017-04-25 at 12:18 +0900, Michel Dänzer wrote:
> > On 24/04/17 03:25 PM, Gerd Hoffmann wrote:
> > > Return correct fourcc codes on bigendian. Drivers must be adapted to
> > > this change.
> > >
> > > Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> >
> > Just to reiterate, this won't work for the radeon driver, which programs
> > the GPU to use (effectively, per the current definition that these are
> > little endian GPU formats) DRM_FORMAT_XRGB8888 with pre-R600 and
> > DRM_FORMAT_BGRX8888 with >= R600.
>
> Hmm, ok, how does bigendian fbdev emulation work on pre-R600 then?
>
> > > +#ifdef __BIG_ENDIAN
> > > + switch (bpp) {
> > > + case 8:
> > > + fmt = DRM_FORMAT_C8;
> > > + break;
> > > + case 24:
> > > + fmt = DRM_FORMAT_BGR888;
> > > + break;
> >
> > BTW, endianness as a concept cannot apply to 8 or 24 bpp formats.
>
> I could move the 8 bpp case out of the #ifdef somehow, but code
> readability will suffer then I think ...
How about something like this?
uint32_t drm_mode_legacy_fb_format(uint32_t bpp, uint32_t depth)
{
uint32_t fmt;
#ifdef __BIG_ENDIAN
enum { LITTLE_ENDIAN = 0 };
#else
enum { LITTLE_ENDIAN = 1 };
#endif
/* ... */
(using an enum for compile-time constness)
and then
fmt = DRM_FORMAT_ARGB8888;
becomes
fmt = LITTLE_ENDIAN ? DRM_FORMAT_ARGB8888 : DRM_FORMAT_BGRA8888;
Might be easier to read than duplicating the whole switch?
>
> For 24 we have different byte orderings, but yes, you can't switch from
> one to the other with byteswapping. Probably one of the reasons why
> this format is pretty much out of fashion these days ...
>
> cheers,
> Gerd
>
