ast: resolutions that require single-buffering (due to VRAM limitations) are unavailable
Thomas Zimmermann
tzimmermann at suse.de
Tue Oct 25 07:36:57 UTC 2022
Hi
Am 25.10.22 um 09:12 schrieb Jeremy Rand:
> Hi dri-devel,
>
> I have two machines with ASPEED GPU's (ast Linux driver). One machine
> is x86_64, running an ASRock Rack Tommy 90-SC02P1-00UBNZ GPU (AST2510
> chipset) with KDE Plasma Wayland; the other is ppc64le, running an
> integrated AST2500 GPU with KDE Plasma X11. Both the AST2510 and
> AST2500 have 16 MiB VRAM according to lspci. Both ASPEED GPU's are
> advertised as supporting up to 1920x1200 resolution, but KDE only
> detects a maximum resolution of 1920x1080.
>
> Some additional information about this bug can be found at
> https://forums.raptorcs.com/index.php/topic,31.0.html .
>
> I believe this is a Linux bug, because it is solely dependent on the
> Linux version. The following Linux versions are confirmed to have the bug:
>
> Debian:
> 5.6.0-1 (ppc64el)
> Fedora:
> 5.6.0-1.fc33.x86_64
> 5.6.0-1.fc33.ppc64le
> 5.17.5-300.fc36.x86_64
> 5.18.6-200.fc36.ppc64le
> 6.1.0-0.rc0.20221007git4c86114194e6.5.fc38.ppc64le
>
> Whereas the following Linux versions are confirmed to work fine (max
> resolution detected by KDE is 1920x1200 as it should be, and that
> resolution works fine when selected):
>
> Debian:
> 5.5.0-2 (ppc64el)
> Fedora:
> 5.5.17-200.fc31.x86_64
> 5.5.17-200.fc31.ppc64le
>
> I believe the bug was introduced by Linux commit
> 9253f830c9166bfa6cc07d5ed59e174e9d5ec6ca, which adds a VRAM size check
> that assumes double-buffering. 1920x1080 resolution at 4 bytes per
> pixel with 2 buffers is 16.6 MB, while bumping that to 1920x1200 results
> in 18.4 MB. Since the VRAM size is 16 MiB == 16.8 MB, that explains the
> issue.
Thanks for reporting. It's been a known issue for a while.
But in the most recent devel tree, we have replaced ast memory
management, so that it can now use the full vram size for scanout
buffers. See
https://cgit.freedesktop.org/drm/drm-tip/commit/drivers/gpu/drm/ast/ast_mode.c?id=f2fa5a99ca81ce1056539e83c705f3d6bec62e31
To test, get the latest drm-tip from
git://anongit.freedesktop.org/drm/drm-tip
and try on your machine.
The updated driver should become available in Linux v6.3.
Best regards
Thomas
>
> Steps to reproduce:
>
> * Add a GPU that uses the ast driver, which supports 1920x1200
> resolution and has 16 MiB VRAM.
> * Boot into KDE.
> * Go to KDE System Settings -> Display and Monitor -> Display
> Configuration.
> * Look at list of detected resolutions.
> * KDE will only detect up to 1920x1080 resolution.
>
> I'm attaching the output of "journalctl --no-hostname -k", although I'm
> doubtful that anything useful is in the log.
>
> I reported this bug to Fedora at
> https://bugzilla.redhat.com/show_bug.cgi?id=2136950 , and was directed
> to this mailing list.
>
> Happy to provide more details on request. (I'm not subscribed to this
> list, so please CC any replies to me.)
>
> Cheers,
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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