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Date:   Fri, 21 Apr 2017 10:49:49 -0400
From:   Ilia Mirkin <imirkin@...m.mit.edu>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        Alex Deucher <alexdeucher@...il.com>,
        amd-gfx@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: fourcc byteorder: brings header file comments in
 line with reality.

On Fri, Apr 21, 2017 at 3:58 AM, Gerd Hoffmann <kraxel@...hat.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.

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@...ux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@...el.com>
> Cc: Pekka Paalanen <ppaalanen@...il.com>
> Cc: Ilia Mirkin <imirkin@...m.mit.edu>
> Cc: Michel Dänzer <michel@...nzer.net>
> Cc: Alex Deucher <alexdeucher@...il.com>
> Cc: amd-gfx@...ts.freedesktop.org
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.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
>

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