[4/4] drm/i915/display: Set TRANS_DDI_MODE_SELECT to default value when disabling TRANS_DDI
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Message ID 20200117015837.402239-4-jose.souza@intel.com
State New
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  • [1/4] drm/mst: Don't do atomic checks over disabled managers
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Commit Message

Souza, Jose Jan. 17, 2020, 1:58 a.m. UTC
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(+)

Comments

Ville Syrjälä Jan. 30, 2020, 5:25 p.m. UTC | #1
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.

>  
>  	if (INTEL_GEN(dev_priv) >= 12) {
>  		if (!intel_dp_mst_is_master_trans(crtc_state))
> -- 
> 2.25.0
Souza, Jose Jan. 30, 2020, 8:07 p.m. UTC | #2
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
Ville Syrjälä Jan. 31, 2020, 11:20 a.m. UTC | #3
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@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.

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
Stanislav Lisovskiy Feb. 11, 2020, 11:23 a.m. UTC | #4
On Thu, 2020-01-16 at 17:58 -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(+)

BAT/IGT are fine, so if this improves some MST behaviors don't see
any point in holding this patch from being merged. 
For MST, we are anyway facing MST regressions almost on weekly basis.
Until we have some meaningful tests in CI for MST, it anyway
would be constantly in "bad" shape.

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>

> 
> 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;
>  
>  	if (INTEL_GEN(dev_priv) >= 12) {
>  		if (!intel_dp_mst_is_master_trans(crtc_state))
Sharma, Swati2 May 13, 2020, 8:28 a.m. UTC | #5
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@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.
> 
> 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?

> 
>>
>>>
>>>>   
>>>>   	if (INTEL_GEN(dev_priv) >= 12) {
>>>>   		if (!intel_dp_mst_is_master_trans(crtc_state))
>>>> -- 
>>>> 2.25.0
>
Ville Syrjälä May 13, 2020, 12:09 p.m. UTC | #6
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@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.
> > 
> > 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 May 13, 2020, 12:14 p.m. UTC | #7
On Wed, May 13, 2020 at 03:09:52PM +0300, Ville Syrjälä wrote:
> 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@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.
> > > 
> > > 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.

If if there is no difference then it may become a fun task of trial and
error to see what about the current order the hardware doesn't like.

Patch
diff mbox series

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