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

["Souza, Jose" <jose.souza@intel.com>]

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@linux.intel.com>
> > Cc: Matt Roper <matthew.d.roper@intel.com>
> > Signed-off-by: José Roberto de Souza <jose.souza@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.

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