Re: [PATCH] drm: fourcc byteorder: brings header file comments in line with reality.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Apr 21, 2017 at 10:49:49AM -0400, Ilia Mirkin wrote:
> On Fri, Apr 21, 2017 at 3:58 AM, Gerd Hoffmann <kraxel@redhat.com> wrote:
> > While working on graphics support for virtual machines on ppc64 (which
> > exists in both little and big endian variants) I've figured the comments
> > for various drm fourcc formats in the header file don't match reality.
> >
> > Comments says the RGB formats are little endian, but in practice they
> > are native endian.  Look at the drm_mode_legacy_fb_format() helper.  It
> > maps -- for example -- bpp/depth 32/24 to DRM_FORMAT_XRGB8888, no matter
> > whenever the machine is little endian or big endian.  The users of this
> > function (fbdev emulation, DRM_IOCTL_MODE_ADDFB) expect the framebuffer
> > is native endian, not little endian.  Most userspace also operates on
> > native endian only.
> >
> > So, go update the comments for all 16+24+32 bpp RGB formats.
> >
> > Leaving the yuv formats as-is.  I have no idea if and how those are used
> > on bigendian machines.
> 
> I think this is premature. The current situation is that I can't get
> modetest to work *at all* on my NV34 / BE setup (I mean, it runs, just
> the colors displayed are wrong). I believe that currently it packs
> things in "cpu native endian". I've tried futzing with that without
> much success, although I didn't spend too much time on it. I have a
> NV34 plugged into my LE setup as well although I haven't tested to
> double-check that it all works there. However I'm quite sure it used
> to, as I used modetest to help develop the YUV overlay support for
> those GPUs.

I just took a quick stab at fixing modetest to respect the current
wording in drm_fourcc.h:

git://github.com/vsyrjala/libdrm.git modetest_endian

> 
> Does modetest work for you, under any interpretation of the formats?
> 
> There's an additional complication wrt looking at what fbcon does,
> since it will feed the data in via special accel interfaces in fbdev,
> which at least on nouveau, may end up byteswapping the data on upload
> to VRAM (I'm not 100% clear on whether they do or not). However
> modetest, which is creating its own fb, likely won't get such
> treatment.
> 
> This is a shitty situation - we have hardware we don't know how it
> works, tools we don't know whether they're broken, and comments we're
> pretty sure are at least somewhat wrong. Furthermore the hardware is
> relatively rare and developers with time to work on improving it are
> even rarer.
> 
> I'd like to reiterate that the status quo does end up in a functioning
> system. Let's try not to break that.
> 
> Cheers,
> 
>   -ilia
> 
> >
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Pekka Paalanen <ppaalanen@gmail.com>
> > Cc: Ilia Mirkin <imirkin@alum.mit.edu>
> > Cc: Michel Dänzer <michel@daenzer.net>
> > Cc: Alex Deucher <alexdeucher@gmail.com>
> > Cc: amd-gfx@lists.freedesktop.org
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > ---
> >  include/uapi/drm/drm_fourcc.h | 82 +++++++++++++++++++++----------------------
> >  1 file changed, 41 insertions(+), 41 deletions(-)
> >
> > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> > index 995c8f9..1579765 100644
> > --- a/include/uapi/drm/drm_fourcc.h
> > +++ b/include/uapi/drm/drm_fourcc.h
> > @@ -42,68 +42,68 @@ extern "C" {
> >  #define DRM_FORMAT_R8          fourcc_code('R', '8', ' ', ' ') /* [7:0] R */
> >
> >  /* 16 bpp Red */
> > -#define DRM_FORMAT_R16         fourcc_code('R', '1', '6', ' ') /* [15:0] R little endian */
> > +#define DRM_FORMAT_R16         fourcc_code('R', '1', '6', ' ') /* [15:0] R native endian */
> >
> >  /* 16 bpp RG */
> > -#define DRM_FORMAT_RG88                fourcc_code('R', 'G', '8', '8') /* [15:0] R:G 8:8 little endian */
> > -#define DRM_FORMAT_GR88                fourcc_code('G', 'R', '8', '8') /* [15:0] G:R 8:8 little endian */
> > +#define DRM_FORMAT_RG88                fourcc_code('R', 'G', '8', '8') /* [15:0] R:G 8:8 native endian */
> > +#define DRM_FORMAT_GR88                fourcc_code('G', 'R', '8', '8') /* [15:0] G:R 8:8 native endian */
> >
> >  /* 32 bpp RG */
> > -#define DRM_FORMAT_RG1616      fourcc_code('R', 'G', '3', '2') /* [31:0] R:G 16:16 little endian */
> > -#define DRM_FORMAT_GR1616      fourcc_code('G', 'R', '3', '2') /* [31:0] G:R 16:16 little endian */
> > +#define DRM_FORMAT_RG1616      fourcc_code('R', 'G', '3', '2') /* [31:0] R:G 16:16 native endian */
> > +#define DRM_FORMAT_GR1616      fourcc_code('G', 'R', '3', '2') /* [31:0] G:R 16:16 native endian */
> >
> >  /* 8 bpp RGB */
> >  #define DRM_FORMAT_RGB332      fourcc_code('R', 'G', 'B', '8') /* [7:0] R:G:B 3:3:2 */
> >  #define DRM_FORMAT_BGR233      fourcc_code('B', 'G', 'R', '8') /* [7:0] B:G:R 2:3:3 */
> >
> >  /* 16 bpp RGB */
> > -#define DRM_FORMAT_XRGB4444    fourcc_code('X', 'R', '1', '2') /* [15:0] x:R:G:B 4:4:4:4 little endian */
> > -#define DRM_FORMAT_XBGR4444    fourcc_code('X', 'B', '1', '2') /* [15:0] x:B:G:R 4:4:4:4 little endian */
> > -#define DRM_FORMAT_RGBX4444    fourcc_code('R', 'X', '1', '2') /* [15:0] R:G:B:x 4:4:4:4 little endian */
> > -#define DRM_FORMAT_BGRX4444    fourcc_code('B', 'X', '1', '2') /* [15:0] B:G:R:x 4:4:4:4 little endian */
> > +#define DRM_FORMAT_XRGB4444    fourcc_code('X', 'R', '1', '2') /* [15:0] x:R:G:B 4:4:4:4 native endian */
> > +#define DRM_FORMAT_XBGR4444    fourcc_code('X', 'B', '1', '2') /* [15:0] x:B:G:R 4:4:4:4 native endian */
> > +#define DRM_FORMAT_RGBX4444    fourcc_code('R', 'X', '1', '2') /* [15:0] R:G:B:x 4:4:4:4 native endian */
> > +#define DRM_FORMAT_BGRX4444    fourcc_code('B', 'X', '1', '2') /* [15:0] B:G:R:x 4:4:4:4 native endian */
> >
> > -#define DRM_FORMAT_ARGB4444    fourcc_code('A', 'R', '1', '2') /* [15:0] A:R:G:B 4:4:4:4 little endian */
> > -#define DRM_FORMAT_ABGR4444    fourcc_code('A', 'B', '1', '2') /* [15:0] A:B:G:R 4:4:4:4 little endian */
> > -#define DRM_FORMAT_RGBA4444    fourcc_code('R', 'A', '1', '2') /* [15:0] R:G:B:A 4:4:4:4 little endian */
> > -#define DRM_FORMAT_BGRA4444    fourcc_code('B', 'A', '1', '2') /* [15:0] B:G:R:A 4:4:4:4 little endian */
> > +#define DRM_FORMAT_ARGB4444    fourcc_code('A', 'R', '1', '2') /* [15:0] A:R:G:B 4:4:4:4 native endian */
> > +#define DRM_FORMAT_ABGR4444    fourcc_code('A', 'B', '1', '2') /* [15:0] A:B:G:R 4:4:4:4 native endian */
> > +#define DRM_FORMAT_RGBA4444    fourcc_code('R', 'A', '1', '2') /* [15:0] R:G:B:A 4:4:4:4 native endian */
> > +#define DRM_FORMAT_BGRA4444    fourcc_code('B', 'A', '1', '2') /* [15:0] B:G:R:A 4:4:4:4 native endian */
> >
> > -#define DRM_FORMAT_XRGB1555    fourcc_code('X', 'R', '1', '5') /* [15:0] x:R:G:B 1:5:5:5 little endian */
> > -#define DRM_FORMAT_XBGR1555    fourcc_code('X', 'B', '1', '5') /* [15:0] x:B:G:R 1:5:5:5 little endian */
> > -#define DRM_FORMAT_RGBX5551    fourcc_code('R', 'X', '1', '5') /* [15:0] R:G:B:x 5:5:5:1 little endian */
> > -#define DRM_FORMAT_BGRX5551    fourcc_code('B', 'X', '1', '5') /* [15:0] B:G:R:x 5:5:5:1 little endian */
> > +#define DRM_FORMAT_XRGB1555    fourcc_code('X', 'R', '1', '5') /* [15:0] x:R:G:B 1:5:5:5 native endian */
> > +#define DRM_FORMAT_XBGR1555    fourcc_code('X', 'B', '1', '5') /* [15:0] x:B:G:R 1:5:5:5 native endian */
> > +#define DRM_FORMAT_RGBX5551    fourcc_code('R', 'X', '1', '5') /* [15:0] R:G:B:x 5:5:5:1 native endian */
> > +#define DRM_FORMAT_BGRX5551    fourcc_code('B', 'X', '1', '5') /* [15:0] B:G:R:x 5:5:5:1 native endian */
> >
> > -#define DRM_FORMAT_ARGB1555    fourcc_code('A', 'R', '1', '5') /* [15:0] A:R:G:B 1:5:5:5 little endian */
> > -#define DRM_FORMAT_ABGR1555    fourcc_code('A', 'B', '1', '5') /* [15:0] A:B:G:R 1:5:5:5 little endian */
> > -#define DRM_FORMAT_RGBA5551    fourcc_code('R', 'A', '1', '5') /* [15:0] R:G:B:A 5:5:5:1 little endian */
> > -#define DRM_FORMAT_BGRA5551    fourcc_code('B', 'A', '1', '5') /* [15:0] B:G:R:A 5:5:5:1 little endian */
> > +#define DRM_FORMAT_ARGB1555    fourcc_code('A', 'R', '1', '5') /* [15:0] A:R:G:B 1:5:5:5 native endian */
> > +#define DRM_FORMAT_ABGR1555    fourcc_code('A', 'B', '1', '5') /* [15:0] A:B:G:R 1:5:5:5 native endian */
> > +#define DRM_FORMAT_RGBA5551    fourcc_code('R', 'A', '1', '5') /* [15:0] R:G:B:A 5:5:5:1 native endian */
> > +#define DRM_FORMAT_BGRA5551    fourcc_code('B', 'A', '1', '5') /* [15:0] B:G:R:A 5:5:5:1 native endian */
> >
> > -#define DRM_FORMAT_RGB565      fourcc_code('R', 'G', '1', '6') /* [15:0] R:G:B 5:6:5 little endian */
> > -#define DRM_FORMAT_BGR565      fourcc_code('B', 'G', '1', '6') /* [15:0] B:G:R 5:6:5 little endian */
> > +#define DRM_FORMAT_RGB565      fourcc_code('R', 'G', '1', '6') /* [15:0] R:G:B 5:6:5 native endian */
> > +#define DRM_FORMAT_BGR565      fourcc_code('B', 'G', '1', '6') /* [15:0] B:G:R 5:6:5 native endian */
> >
> >  /* 24 bpp RGB */
> > -#define DRM_FORMAT_RGB888      fourcc_code('R', 'G', '2', '4') /* [23:0] R:G:B little endian */
> > -#define DRM_FORMAT_BGR888      fourcc_code('B', 'G', '2', '4') /* [23:0] B:G:R little endian */
> > +#define DRM_FORMAT_RGB888      fourcc_code('R', 'G', '2', '4') /* [23:0] R:G:B native endian */
> > +#define DRM_FORMAT_BGR888      fourcc_code('B', 'G', '2', '4') /* [23:0] B:G:R native endian */
> >
> >  /* 32 bpp RGB */
> > -#define DRM_FORMAT_XRGB8888    fourcc_code('X', 'R', '2', '4') /* [31:0] x:R:G:B 8:8:8:8 little endian */
> > -#define DRM_FORMAT_XBGR8888    fourcc_code('X', 'B', '2', '4') /* [31:0] x:B:G:R 8:8:8:8 little endian */
> > -#define DRM_FORMAT_RGBX8888    fourcc_code('R', 'X', '2', '4') /* [31:0] R:G:B:x 8:8:8:8 little endian */
> > -#define DRM_FORMAT_BGRX8888    fourcc_code('B', 'X', '2', '4') /* [31:0] B:G:R:x 8:8:8:8 little endian */
> > +#define DRM_FORMAT_XRGB8888    fourcc_code('X', 'R', '2', '4') /* [31:0] x:R:G:B 8:8:8:8 native endian */
> > +#define DRM_FORMAT_XBGR8888    fourcc_code('X', 'B', '2', '4') /* [31:0] x:B:G:R 8:8:8:8 native endian */
> > +#define DRM_FORMAT_RGBX8888    fourcc_code('R', 'X', '2', '4') /* [31:0] R:G:B:x 8:8:8:8 native endian */
> > +#define DRM_FORMAT_BGRX8888    fourcc_code('B', 'X', '2', '4') /* [31:0] B:G:R:x 8:8:8:8 native endian */
> >
> > -#define DRM_FORMAT_ARGB8888    fourcc_code('A', 'R', '2', '4') /* [31:0] A:R:G:B 8:8:8:8 little endian */
> > -#define DRM_FORMAT_ABGR8888    fourcc_code('A', 'B', '2', '4') /* [31:0] A:B:G:R 8:8:8:8 little endian */
> > -#define DRM_FORMAT_RGBA8888    fourcc_code('R', 'A', '2', '4') /* [31:0] R:G:B:A 8:8:8:8 little endian */
> > -#define DRM_FORMAT_BGRA8888    fourcc_code('B', 'A', '2', '4') /* [31:0] B:G:R:A 8:8:8:8 little endian */
> > +#define DRM_FORMAT_ARGB8888    fourcc_code('A', 'R', '2', '4') /* [31:0] A:R:G:B 8:8:8:8 native endian */
> > +#define DRM_FORMAT_ABGR8888    fourcc_code('A', 'B', '2', '4') /* [31:0] A:B:G:R 8:8:8:8 native endian */
> > +#define DRM_FORMAT_RGBA8888    fourcc_code('R', 'A', '2', '4') /* [31:0] R:G:B:A 8:8:8:8 native endian */
> > +#define DRM_FORMAT_BGRA8888    fourcc_code('B', 'A', '2', '4') /* [31:0] B:G:R:A 8:8:8:8 native endian */
> >
> > -#define DRM_FORMAT_XRGB2101010 fourcc_code('X', 'R', '3', '0') /* [31:0] x:R:G:B 2:10:10:10 little endian */
> > -#define DRM_FORMAT_XBGR2101010 fourcc_code('X', 'B', '3', '0') /* [31:0] x:B:G:R 2:10:10:10 little endian */
> > -#define DRM_FORMAT_RGBX1010102 fourcc_code('R', 'X', '3', '0') /* [31:0] R:G:B:x 10:10:10:2 little endian */
> > -#define DRM_FORMAT_BGRX1010102 fourcc_code('B', 'X', '3', '0') /* [31:0] B:G:R:x 10:10:10:2 little endian */
> > +#define DRM_FORMAT_XRGB2101010 fourcc_code('X', 'R', '3', '0') /* [31:0] x:R:G:B 2:10:10:10 native endian */
> > +#define DRM_FORMAT_XBGR2101010 fourcc_code('X', 'B', '3', '0') /* [31:0] x:B:G:R 2:10:10:10 native endian */
> > +#define DRM_FORMAT_RGBX1010102 fourcc_code('R', 'X', '3', '0') /* [31:0] R:G:B:x 10:10:10:2 native endian */
> > +#define DRM_FORMAT_BGRX1010102 fourcc_code('B', 'X', '3', '0') /* [31:0] B:G:R:x 10:10:10:2 native endian */
> >
> > -#define DRM_FORMAT_ARGB2101010 fourcc_code('A', 'R', '3', '0') /* [31:0] A:R:G:B 2:10:10:10 little endian */
> > -#define DRM_FORMAT_ABGR2101010 fourcc_code('A', 'B', '3', '0') /* [31:0] A:B:G:R 2:10:10:10 little endian */
> > -#define DRM_FORMAT_RGBA1010102 fourcc_code('R', 'A', '3', '0') /* [31:0] R:G:B:A 10:10:10:2 little endian */
> > -#define DRM_FORMAT_BGRA1010102 fourcc_code('B', 'A', '3', '0') /* [31:0] B:G:R:A 10:10:10:2 little endian */
> > +#define DRM_FORMAT_ARGB2101010 fourcc_code('A', 'R', '3', '0') /* [31:0] A:R:G:B 2:10:10:10 native endian */
> > +#define DRM_FORMAT_ABGR2101010 fourcc_code('A', 'B', '3', '0') /* [31:0] A:B:G:R 2:10:10:10 native endian */
> > +#define DRM_FORMAT_RGBA1010102 fourcc_code('R', 'A', '3', '0') /* [31:0] R:G:B:A 10:10:10:2 native endian */
> > +#define DRM_FORMAT_BGRA1010102 fourcc_code('B', 'A', '3', '0') /* [31:0] B:G:R:A 10:10:10:2 native endian */
> >
> >  /* packed YCbCr */
> >  #define DRM_FORMAT_YUYV                fourcc_code('Y', 'U', 'Y', 'V') /* [31:0] Cr0:Y1:Cb0:Y0 8:8:8:8 little endian */
> > --
> > 2.9.3
> >

-- 
Ville Syrjälä
Intel OTC