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SubjectRe: [RfC PATCH] drm: fourcc byteorder: brings header file comments in line with reality.
On Tue, 18 Apr 2017 12:00:17 +0200
Gerd Hoffmann <kraxel@redhat.com> wrote:

> Hi,
>
> > > ppc64 (big endian) virtual machine, running with qemu stdvga & bochs-drm
> > > driver. Xorg with modesetting driver uses DRM_FORMAT_XRGB8888 (one and
> > > only format supported by bochs-drm), and we have to interpret that in
> > > bigendian byte order on the host side to get a correct display.
> >
> > I wonder if that is just an oversight from trying to match OpenGL
> > formats to DRM formats. It's full of gotcha's.
> >
> > Did you try with GLAMOR? Do you see a difference with and without
> > GLAMOR? Hmm, but you have no GPU support, so GLAMOR would be through a
> > Mesa software renderer? I think I heard someone say something about
> > Mesa software on BE...
>
> So, did some more testing to see where we stand.
>
> Historical note: RHEL-6.9 (gnome 2) works fine. Not of much interest
> here, it drives the qemu stdvga with offb, not bochs-drm.

I suppose this proves the virtual machine itself is correct about
framebuffer endianess? Except you are running it on a little-endian
host machine I presume...

> More interesting: RHEL-7.3 (gnome 3.14) works fine too. kernel 3.10,
> but drm drivers updated to roughly 4.6 level. Runs bochs-drm. mesa
> 11.2.2. glamour not used.
>
> Most recent: Fedora 25 (gnome 3.22) looks mostly ok, but there are
> rendering glitches, for example in the gnome activities screen (the one
> you get when you press the windows key). kernel 4.10, mesa 13.0.4.
> glamor not used, but I think gnome-shell uses opengl (via llvmpipe) for
> compositing.

I believe glitches are irrelevant for this topic, what we are
interested in is if the colors are right or byte-swapped (also mind
alpha/blue etc. swaps).

> btw: is there some way to start a wayland session from a shell (i.e.
> what startx does for xorg)?

Depends on which display server you want to start I believe. I don't
know about anything else than Weston, which is 'weston' for a
logind-enabled system.


Thanks,
pq
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