Re: [PATCH 19/20] drm/i915/dp: Ack only the handled device service IRQs

[Imre Deak <imre.deak@intel.com>]

On Thu, Jul 03, 2025 at 04:14:51PM +0300, Luca Coelho wrote:
> On Thu, 2025-06-26 at 11:20 +0300, Imre Deak wrote:
> > From: Imre Deak <imre.deak@gmail.com>
> > 
> > Only those IRQs should be acked that are handled, however for SST all
> > IRQs triggered by the sink are acked. This can be a problem for flags
> > that are reserved/reading zero at a given moment, but become used for
> > some purpose - with a side-effect if set - in a future DPCD revision.
> > 
> > Fix the above by acking only those device service IRQs that will be
> > handled. While at it add asserts that only the known/acked device
> > service IRQs are handled both in the MST and SST case.
> > 
> > Signed-off-by: Imre Deak <imre.deak@gmail.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 52249fa5c8a6d..6f67fac9724e1 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -4537,6 +4537,14 @@ intel_dp_mst_disconnect(struct intel_dp *intel_dp)
> >  	drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst.mgr, intel_dp->is_mst);
> >  }
> >  
> > +#define INTEL_DP_DEVICE_SERVICE_IRQ_MASK_SST	(DP_AUTOMATED_TEST_REQUEST | \
> > +						 DP_CP_IRQ | \
> > +						 DP_SINK_SPECIFIC_IRQ)
> > +
> > +#define INTEL_DP_DEVICE_SERVICE_IRQ_MASK_MST	(DP_CP_IRQ | \
> > +						 DP_DOWN_REP_MSG_RDY | \
> > +						 DP_UP_REQ_MSG_RDY)
> > +
> >  static bool
> >  intel_dp_get_sink_irq_esi(struct intel_dp *intel_dp, u8 *esi)
> >  {
> > @@ -4628,6 +4636,8 @@ static bool intel_dp_get_and_ack_sink_irq_esi_sst(struct intel_dp *intel_dp, u8
> >  		    encoder->base.base.id, encoder->base.name,
> >  		    esi);
> >  
> > +	esi[1] &= INTEL_DP_DEVICE_SERVICE_IRQ_MASK_SST;
> > +
> >  	if (mem_is_zero(&esi[1], 3))
> >  		return true;
> >  
> > @@ -5172,6 +5182,8 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> >  		if (mem_is_zero(ack, sizeof(ack)))
> >  			break;
> >  
> > +		drm_WARN_ON(display->drm, ack[1] & ~INTEL_DP_DEVICE_SERVICE_IRQ_MASK_MST);
> > +
> >  		if (!intel_dp_ack_sink_irq_esi(intel_dp, ack))
> >  			drm_dbg_kms(display->drm, "Failed to ack ESI\n");
> >  
> > @@ -5456,6 +5468,8 @@ static void intel_dp_handle_device_service_irq(struct intel_dp *intel_dp, u8 irq
> >  {
> >  	struct intel_display *display = to_intel_display(intel_dp);
> >  
> > +	drm_WARN_ON(display->drm, irq_mask & ~INTEL_DP_DEVICE_SERVICE_IRQ_MASK_SST);
> > +
> >  	if (irq_mask & DP_AUTOMATED_TEST_REQUEST)
> >  		intel_dp_test_request(intel_dp);
> >  
> 
> Evidently, this function is specific to SST irq.  Wouldn't it be better
> to have _sst in the name like in "intel_dp_check_mst_status()"? This
> function is probably in an earlier patch, though, so if handled it
> should be obviously be done there.

Yes, it used to be SST specific, but patch 18 reused it for MST as well.

> Otherwise:
> 
> Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
> 
> --
> Cheers,
> Luca.