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

[Carroll, Lewis]

> -----Original Message-----
> From: daniel.vetter at ffwll.ch [mailto:daniel.vetter at ffwll.ch] On Behalf Of
> Daniel Vetter
> Sent: Thursday, December 21, 2017 3:31 PM
> To: Carroll, Lewis <Lewis.Carroll at amd.com>; Daenzer, Michel
> <Michel.Daenzer at amd.com>
> Cc: Wentland, Harry <Harry.Wentland at amd.com>; dri-
> devel at lists.freedesktop.org
> Subject: Re: drm/ast: Linux 4.14 AST DRM driver might not load gamma table
> [patch proposed]
> 
> Fyi Michel, we've discussed similar issues for radeon/amdgpu on irc.
> 
> On Thu, Dec 21, 2017 at 4:21 PM, Carroll, Lewis <Lewis.Carroll at amd.com>
> wrote:
> >> -----Original Message-----
> >> From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel
> >> Vetter
> >> Sent: Thursday, December 21, 2017 5:07 AM
> >> To: Carroll, Lewis <Lewis.Carroll at amd.com>
> >> Cc: Wentland, Harry <Harry.Wentland at amd.com>; dri-
> >> devel at lists.freedesktop.org
> >> Subject: Re: drm/ast: Linux 4.14 AST DRM driver might not load gamma
> table
> >> [patch proposed]
> >>
> >> On Thu, Dec 21, 2017 at 12:00:39AM +0000, Carroll, Lewis wrote:
> >> > The discussion sounds similar as well - related to load_lut() not being
> called.
> >> >
> >> > Perhaps after the drm-next-4.14 merge, whatever call stack used to
> cause
> >> > load_lut to always get called is now gone. Even if
> FB_VISUAL_TRUECOLOR
> >> > doesn't support a clut, some hardware may still need a default gamma
> lut
> >> > loaded (appears to be the case with the AST2500). Perhaps checking for
> >> > that profile and loading the default LUT prepared by
> >> > drm_mode_crtc_set_gamma_size when FB_VISUAL_TRUECOLOR...?
> >>
> >> Yeah drivers should load that somehow. Unfortunately I'm going on
> >> vacations now, so I'm not going to fix anything anytime soon. Might be
> >> good to ping Peter Rosin, he did all the fbdev emulation gamma handling
> >> rework (which is the patch that removed the superflously-looking call to
> >> ->load_lut that some drivers relied on to have a consistent lut state).
> >> -Daniel
> >
> > Enjoy the holidays.
> >
> > Wonder if it would be better to just call load_lut after
> > drm_mode_crtc_set_gamma_size instead of adding a potentially
> > unnecessary DPMS ON event to the commit call-back as I did...? Or call
> > load_lut in the commit callback instead of the DPMS ON call...?
> >
> > The first approach (calling load_lut after set_gamma_size) also works on
> > two test systems.
> 
> Yeah, I think that's the cleanest approach. The underlying issue is
> that a bunch of drivers are not making sure that on driver-load they
> have a consistent sw/hw state for the gamma ramp. As long as you had
> fbcon enabled the strange ->load_lut call (which isn't really
> necessary for drivers that got this right) papered over these issues.
> 
> So a call to you driver's load_lut right affter
> drm_mode_crtc_set_gamma_size should fix this correctly. a-b:me if you
> submit that patch.

Reworked patch attached, commit message changed to summarize the
Above discussion.

> 
> /me off for real now
> 
> Cheers, Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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