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

[Ville Syrjälä]

On Wed, May 13, 2020 at 01:58:47PM +0530, Sharma, Swati2 wrote:
> 
> 
> On 31-Jan-20 4:50 PM, Ville Syrjälä wrote:
> > 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.
> 
> Hi Ville/Jose,
> 
> We are still observing
> =>*ERROR* Timed out waiting for ACT sent when disabling
> =>FIFO underruns
> Do we need a change disable sequence?

My crystal ball is foggy today. If you want to know whether there is a
mismatch between the spec and code you're just going to have to read
both and compare.

-- 
Ville Syrjälä
Intel