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Date:   Thu, 16 Nov 2023 15:44:47 +0100
From:   Gerd Hoffmann <kraxel@redhat.com>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Christian Zigotzky <chzigotzky@xenosoft.de>,
        David Airlie <airlied@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Laurent Vivier <lvivier@redhat.com>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Hamza Mahfooz <hamza.mahfooz@amd.com>,
        linux-m68k@lists.linux-m68k.org, dri-devel@lists.freedesktop.org,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] drm/virtio: Add suppport for non-native buffer formats
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References: <47a81d2e0e47b1715718779b6978a8b595cc7c5d.1700140609.git.geert@linux-m68k.org>
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On Thu, Nov 16, 2023 at 02:16:54PM +0100, Geert Uytterhoeven wrote:
> When using virtgpu on a big-endian machine, e.g. powerpc QEMU:
> 
>     virtio-pci 0000:00:02.0: [drm] *ERROR* fbdev: Failed to setup generic emulation (ret=-2)
> 
> or m68k/virt:
> 
>     virtio-mmio virtio-mmio.125: [drm] *ERROR* fbdev: Failed to setup generic emulation (ret=-2)
> 
> and the graphical display fails to come up.
> 
> Before, the call to drm_mode_addfb() caused a translation from a fourcc
> format (XR24) to a bpp/depth pair (32/24) to a potentially different fourcc
> format (BX24 on big-endian), due to the quirk processing in
> drm_driver_legacy_fb_format().  After, the original fourcc format (XR24)
> is passed unmodified.
> 
> However, the virtgpu DRM driver supports only a single format for its
> main plane: DRM_FORMAT_HOST_XRGB8888, which is XR24 on little-endian,
> and BX24 on big-endian.  I.e. on big-endian, virtgpu does not support
> XR24, which is the default DRM format, and must be supported by all
> drivers.  Before, this was reported, but didn't lead to a failure:
> 
>     virtio-mmio virtio-mmio.125: [drm] bpp/depth value of 32/24 not supported
>     virtio-mmio virtio-mmio.125: [drm] No compatible format found
> 
> As the core virtgpu driver and device support both XR24 and BX24 on both
> little-endian and big-endian just fine, fix this extending the list of
> supported formats for main plane and cursor plane to XR24/BX24 resp.
> AR24/BA24.
> 
> Fixes: 6ae2ff23aa43a0c4 ("drm/client: Convert drm_client_buffer_addfb() to drm_mode_addfb2()")
> Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
> Closes: https://lore.kernel.org/r/c47fba21-3ae9-4021-9f4a-09c2670ebdbc@xenosoft.de
> Suggested-by: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>