[PATCH 4/4] drm/i915/display: Set TRANS_DDI_MODE_SELECT to default value when disabling TRANS_DDI

[Ville Syrjälä]

On Thu, Jan 30, 2020 at 08:07:07PM +0000, Souza, Jose wrote:
> On Thu, 2020-01-30 at 19:25 +0200, Ville Syrjälä wrote:
> > On Thu, Jan 16, 2020 at 05:58:37PM -0800, José Roberto de Souza
> > wrote:
> > > TGL timeouts when disabling MST transcoder and fifo underruns over
> > > MST
> > > transcoders are fixed when setting TRANS_DDI_MODE_SELECT to 0(HDMI
> > > mode) during the disable sequence.
> > > 
> > > Although BSpec disable sequence don't require this step it is a
> > > harmless change and it is also done by Windows driver.
> > > Anyhow HW team was notified about that but it can take some time to
> > > documentation to be updated.
> > > 
> > > A case that always lead to those issues is:
> > > - do a modeset enabling pipe A and pipe B in the same MST stream
> > > leaving A as master
> > > - disable pipe A, promote B as master doing a full modeset in A
> > > - enable pipe A, changing the master transcoder back to A(doing a
> > > full modeset in B)
> > > - Pow: underruns and timeouts
> > > 
> > > The transcoders involved will only work again when complete
> > > disabled
> > > and their power wells turned off causing a reset in their
> > > registers.
> > > 
> > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > Cc: Matt Roper <matthew.d.roper at intel.com>
> > > Signed-off-by: José Roberto de Souza <jose.souza at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_ddi.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c
> > > b/drivers/gpu/drm/i915/display/intel_ddi.c
> > > index 32ea3c7e8b62..82e90f271974 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> > > @@ -1997,6 +1997,7 @@ void intel_ddi_disable_transcoder_func(const
> > > struct intel_crtc_state *crtc_state
> > >  
> > >  	val = I915_READ(TRANS_DDI_FUNC_CTL(cpu_transcoder));
> > >  	val &= ~TRANS_DDI_FUNC_ENABLE;
> > > +	val &= ~TRANS_DDI_MODE_SELECT_MASK;
> > 
> > Feels a bit early since IIRC we still leave a bunch of other stuff
> > enabled/selected here. In fact we don't seem to be clearing the DDI
> > select
> > anywhere at all? That one I would be more suspicious of than the
> > mode.
> > But maybe we should just clear both somewhere? I would suggest it
> > should
> > be when we clear the port select finally.
> 
> We are clearing DDI select, in our code it is named as
> TGL_TRANS_DDI_PORT_MASK/TRANS_DDI_PORT_MASK.
> 
> For TGL in MST mode we clear DDI select in the block below for MST
> slaves and then in intel_ddi_post_disable_dp() for MST master as
> instructed by Display port sequences.

Ah. Hmm, so that can't be it then. Bummer. I guess I would still feel
a bit safer if we clear the mode select alongside the the DDI select
for the master. Since the spec says the DDI select must remain set for
the master there must be something still going on, and so I worry that
something might not work quite right if we change the mode
prematurely.

> 
> > 
> > >  
> > >  	if (INTEL_GEN(dev_priv) >= 12) {
> > >  		if (!intel_dp_mst_is_master_trans(crtc_state))
> > > -- 
> > > 2.25.0

-- 
Ville Syrjälä
Intel