linux-kernel - Re: [PATCH 1/3] drm: fourcc byteorder: drop DRM_FORMAT_BIG

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Message-ID: <20170502172724.31188e2d@eldfell>
Date:   Tue, 2 May 2017 17:27:24 +0300
From:   Pekka Paalanen <ppaalanen@...il.com>
To:     Emil Velikov <emil.l.velikov@...il.com>,
        Gerd Hoffmann <kraxel@...hat.com>
Cc:     ML dri-devel <dri-devel@...ts.freedesktop.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Michel Dänzer <michel@...nzer.net>,
        open list <linux-kernel@...r.kernel.org>,
        amd-gfx mailing list <amd-gfx@...ts.freedesktop.org>,
        Sean Paul <seanpaul@...omium.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Alex Deucher <alexdeucher@...il.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Ilia Mirkin <imirkin@...m.mit.edu>
Subject: Re: [PATCH 1/3] drm: fourcc byteorder: drop DRM_FORMAT_BIG_ENDIAN

On Tue, 2 May 2017 14:53:43 +0100
Emil Velikov <emil.l.velikov@...il.com> wrote:

> Hi Gerd,
> 
> I did not have the change to follow through the discussion.
> Pardon if my suggestion have already been discussed.
> 
> On 2 May 2017 at 14:34, Gerd Hoffmann <kraxel@...hat.com> wrote:
> > It's unused.
> >
> > Suggested-by: Daniel Vetter <daniel.vetter@...el.com>
> > Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> > ---
> >  include/uapi/drm/drm_fourcc.h     | 2 --
> >  drivers/gpu/drm/drm_fourcc.c      | 3 +--
> >  drivers/gpu/drm/drm_framebuffer.c | 2 +-
> >  3 files changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> > index 995c8f9c69..305bc34be0 100644
> > --- a/include/uapi/drm/drm_fourcc.h
> > +++ b/include/uapi/drm/drm_fourcc.h
> > @@ -33,8 +33,6 @@ extern "C" {
> >  #define fourcc_code(a, b, c, d) ((__u32)(a) | ((__u32)(b) << 8) | \
> >                                  ((__u32)(c) << 16) | ((__u32)(d) << 24))
> >
> > -#define DRM_FORMAT_BIG_ENDIAN (1<<31) /* format is big endian instead of little endian */
> > -  
> 
> Weston references DRM_FORMAT_BIG_ENDIAN thus this patch will lead to
> build breakage.
> That is never fun, so please carefully coordinate with the Weston devs
> to minimise the fireworks.
> 
> Personally I would leave the symbol, since it's UAPI and document that
> should not be used. Not my call, so feel free to ignore.

Hi,

indeed, weston does have one occurrence of it. I don't think it has
actually been needed in practice ever, but removing it will cause a
build failure:
https://cgit.freedesktop.org/wayland/weston/tree/libweston/gl-renderer.c?id=2.0.0#n1820
Funnily enough, it's only ever used to get rid of the bit, "just in
case".

I also think that this patch requires more comments than the
commit message has at the moment.

Removing the definition also removes the possibility to describe a lot
of pixel formats, so that should definitely be mentioned. I think it
would also be good to have some kind of justified claim that no
hardware actually needs the pixel formats this is removing (e.g. RGB565
BE). Maybe this was already in the long discussions, but I feel it
should be summarized in the commit message.


Thanks,
pq

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