Re: [PATCH 12/14] drm/i915: Turn on panel power before doing aux transfers

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Aug 19, 2014 at 01:57:57PM +0300, Ville Syrjälä wrote:
> On Tue, Aug 19, 2014 at 10:33:15AM +0300, Jani Nikula wrote:
> > On Mon, 18 Aug 2014, ville.syrjala@linux.intel.com wrote:
> > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > >
> > > On VLV/CHV the panel power sequencer may need to be "kicked" a bit to
> > > lock onto the new port, and that needs to happen before any aux
> > > transfers are attempted if we want the aux transfers to actaully
> > > succeed. So turn on panel power (part of the "kick") before aux
> > > transfers (DPMS_ON + link training).
> > >
> > > This also matches the documented modeset sequence better for pch
> > > platforms. The documentation doesn't explicitly state anything about the
> > > DPMS or link training DPCD writes, but the panel power on step is
> > > always listed before link training is mentioned.
> > >
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > index 4952783..28bc652 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -2275,10 +2275,10 @@ static void intel_enable_dp(struct intel_encoder *encoder)
> > >  		return;
> > >  
> > >  	intel_edp_panel_vdd_on(intel_dp);
> > > -	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> > > -	intel_dp_start_link_train(intel_dp);
> > >  	intel_edp_panel_on(intel_dp);
> > >  	intel_edp_panel_vdd_off(intel_dp, true);
> > > +	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> > > +	intel_dp_start_link_train(intel_dp);
> > 
> > Please dig into the git history in this area. I fear this may
> > regress. We've juggled this too many times...
> 
> I did. But I couldn't spot much solid analysis of the problems in the
> earlier patches/reverts. It's mostly been guesswork AFAICS. Most of it
> seems to be back and forth with the force vdd on/off vs. panel power on,
> but this patch doesn't change that order.
> 
> Also:
> a) we need this patch on VLV/CHV at the very least
> b) this agrees with the bspec modeset sequence for pch platforms better
> c) my ILK with CPU eDP seems happy with the new order

There have been bug reports about ivb/snb cpu edp panels not lighting up
iirc. Especially when the bios didn't light up the panel already (e.g.
when an external screen is plugged in). Might be worth a try to haggle
this patch to those bugs. But I seem to have a hard time finding them
right now :(
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch