[PATCH] drm/i915/dp: Wait more before rearming FIFO underrun during retrain

[Imre Deak]

Atm the link on DP-SST is retrained without a full modeset, which
probably causes an underrun. This was originally done for simplicity,
the underrun not causing further known issues. The plan is to retrain
the link with a full modeset instead on DP-SST as well, similarly to how
this is done on DP-MST already:

https://github.com/ideak/linux/commits/sst-modeset-retrain

On Wed, Jun 26, 2024 at 03:18:32PM +0000, Runyan, Arthur J wrote:
> There is no underrun expected (that I know of) when coming out of
> training on recent product generations.  You should undo this masking
> and debug.
> 
> -----Original Message-----
> From: Vivi, Rodrigo <rodrigo.vivi at intel.com> 
> Sent: Wednesday, June 26, 2024 8:13 AM
> To: Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>; Runyan, Arthur J <arthur.j.runyan at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org
> Subject: Re: [PATCH] drm/i915/dp: Wait more before rearming FIFO underrun during retrain
> 
> On Wed, Jun 26, 2024 at 02:06:24PM +0530, Ankit Nautiyal wrote:
> > During Link re-training reporting underrun is disabled and then 
> > renabled after re-training is completed. For BMG its seen that we get 
> > FIFO underrun just after the retraining is completed and the underrun 
> > reporting is re-enabled.
> > Add one more intel_crtc_wait_for_next_vblank before re-arming the 
> > underruns.
> 
> Cc: Arthur Runyan <arthur.j.runyan at intel.com>
> 
> Art, any new workaround in BMG for this issue?
> 
> > 
> > Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> 
> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c 
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 3903f6ead6e6..25af51499383 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -5325,7 +5325,12 @@ static int intel_dp_retrain_link(struct intel_encoder *encoder,
> >  		const struct intel_crtc_state *crtc_state =
> >  			to_intel_crtc_state(crtc->base.state);
> >  
> > -		/* Keep underrun reporting disabled until things are stable */
> > +		/*
> > +		 * Keep underrun reporting disabled until things are stable.
> > +		 * Wait for some more time, as we see (at least on BMG) that
> > +		 * underrun gets reported just after the reporting is enabled.
> > +		 */
> > +		intel_crtc_wait_for_next_vblank(crtc);
> >  		intel_crtc_wait_for_next_vblank(crtc);
> >  
> >  		intel_set_cpu_fifo_underrun_reporting(dev_priv, crtc->pipe, true);
> > --
> > 2.40.1
> >