[Bug 73530] Asus U38N: Black screen with Radeon driver in Linux

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=73530

--- Comment #86 from N.Leiten <nickleiten@gmail.com> ---
(In reply to Alex Deucher from comment #85)
> (In reply to N.Leiten from comment #84)
> > (In reply to Alex Deucher from comment #83)
> > > Created attachment 115699 [details] [review] [review] [review]
> > > possible fix
> > > 
> > > Is the dpcd information always wrong or just sometimes?  If it's always
> > > wrong, the attached patch might help.  If it's only sometimes wrong, we
> > > probably need to figure out under what conditions it's wrong.
> > 
> > In my case it was always wrong at point of rate/link calculation, but DPCD
> > itself read right, cause I see in dmesg:
> > [drm:radeon_dp_getdpcd] DPCD: 11 0a 84 01 00 0b 01 01 02 00 00 00 00 00 00
> > 
> > According to this DPCD info we need 0x84 value masked with 0x1f which must
> > return maximum of 4 lanes. But in function radeon_dp_get_dp_lane_number I
> > got dpcd with all zeros instead. So I concluded that somewhere in flow it
> > got NULL'ed.
> > 
> 
> Ok, the patch shouldn't be necessary then.
> 
> > 
> > I'll check your patch in two-three hours later, little busy at the moment.
> > But is it wise to make additional copies of same data? Maybe I'm a little
> > paranoid, but I always thought that this method is the last variant of
> > solution due to memory consumption. We need to find, where it blows
> > configuration data so in other configurations it'll work as suspected not
> > only in this combination of eDP and LVDS encoder, please correct me if I'm
> > wrong.
> 
> There's one copy that gets fetched when the displays are probed
> (radeon_dp_getdpcd gets called from radeon_connectors.c).  Then
> radeon_dp_set_link_config() which selects the number of names and link rate
> gets called form radeon_atom_mode_fixup() before the mode is set.

Thanks for points of start :) I'll workout this ASAP.

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