drm/ast: Linux 4.14 AST DRM driver might not load gamma table [patch proposed]

[Harry Wentland]

This looks similar to this bug that I spotted while finally going through my large dri-devel backlog: https://bugzilla.kernel.org/show_bug.cgi?id=198123

The discussion continues here https://lists.freedesktop.org/archives/dri-devel/2017-December/160667.html

Not sure if this is related but the symptoms sound quite similar.

Harry

On 2017-12-17 07:08 PM, Carroll, Lewis wrote:
> Happy Holidays.
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> Test-driving Linux 4.14 from the Ubuntu Bionic repo on an AMD EPYC server using the A-Speed AST2500 BMC and the AST DRM driver and framebuffer console configured into the kernel, I have observed multiple systems where the analog VGA color palette for the framebuffer console is incorrect. Background is blue and all text colors other than white / gray are incorrect.
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> Instrumenting the AST DRM driver, it seems the default gamma table isn’t loaded to the silicon until there is a DPMS action. When there is a DPMS action other than DPMS OFF, the gamma table is loaded and all is well. On these boards, the kernel is not calling for a DPMS event at driver init so the gamma table is not loaded.
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> The attached proposed patch adds a DPMS ON event to the commit callback after a kernel modeset call. This solves the problem, however there may be a better / more proper way to solve this.
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> Assuming no one on the mailing list has hardware on which to verify this, I am happy to be a test driver for any suggested fixes.
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> Regards,
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> Lewis Carroll
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> Principal Solutions Architect
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> AMD Enterprise Business Group
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