On Tue, Jul 01, 2025 at 11:02:30AM +0300, Luca Coelho wrote:
> On Thu, 2025-06-26 at 11:20 +0300, Imre Deak wrote:
> > From: Imre Deak <imre.d...@gmail.com>
> >
> > HPD IRQs in general should be handled after acking them. The
> >
> > 1. Read IRQ register (read DP_DEVICE_SERVICE_IRQ_VECTOR,
> > DP_LINK_SERVICE_IRQ_VECTOR_ESI0)
> > 2. Handle IRQ
> > 3. Ack IRQ (write DP_DEVICE_SERVICE_IRQ_VECTOR,
> > DP_LINK_SERVICE_IRQ_VECTOR_ESI0)
> >
> > sequence would miss a new interrupt triggered after 2. and before 3.,
> > since the flag set in the IRQ register for this interrupt would be
> > cleared in step 3.
> >
> > Fix the above by handling the IRQ after acking it.
> >
> > Signed-off-by: Imre Deak <imre.d...@gmail.com>
> > ---
> > drivers/gpu/drm/i915/display/intel_dp.c | 25 +++++++++++--------------
> > 1 file changed, 11 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 285cd9a5d4a7b..453416b9e9bec 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -5099,17 +5099,10 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> >
> > drm_dbg_kms(display->drm, "DPRX ESI: %4ph\n", esi);
> >
> > - ack[3] |= esi[3] & LINK_STATUS_CHANGED;
> > + ack[3] |= esi[3] & (LINK_STATUS_CHANGED | DP_TUNNELING_IRQ);
> >
> > intel_dp_mst_hpd_irq(intel_dp, esi, ack);
> >
> > - if (esi[3] & DP_TUNNELING_IRQ) {
> > - if (drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr,
> > - &intel_dp->aux))
> > - reprobe_needed = true;
> > - ack[3] |= DP_TUNNELING_IRQ;
> > - }
> > -
> > if (mem_is_zero(ack, sizeof(ack)))
> > break;
>
> What happens if we ack the interrupt, but end up not handling it, e.g.
> if mem_is_zero() returns true here?
This is an optimization in case of ack[] having no bits set (and also to
break from the loop acking->handling IRQs). I.e. if ack[] is zero the
AUX write to ack IRQs in intel_dp_ack_sink_irq_esi() can be skipped,
since no IRQ needs to be acked and then also no IRQ needs to be handled.
> >
> > @@ -5121,6 +5114,10 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
> >
> > if ((ack[3] & LINK_STATUS_CHANGED) ||
> > intel_dp->link.force_retrain)
> > intel_dp_check_link_state(intel_dp);
> > +
> > + if ((ack[3] & DP_TUNNELING_IRQ) &&
> > + drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr,
> > &intel_dp->aux))
> > + reprobe_needed = true;
> > }
> >
> > return !reprobe_needed;
> > @@ -5423,18 +5420,18 @@ static bool intel_dp_check_link_service_irq(struct
> > intel_dp *intel_dp)
> > DP_LINK_SERVICE_IRQ_VECTOR_ESI0, &val) != 1 ||
> > !val)
> > return false;
> >
> > - if ((val & DP_TUNNELING_IRQ) &&
> > - drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr,
> > - &intel_dp->aux))
> > - reprobe_needed = true;
> > -
> > if (drm_dp_dpcd_writeb(&intel_dp->aux,
> > DP_LINK_SERVICE_IRQ_VECTOR_ESI0, val) != 1)
> > - return reprobe_needed;
> > + return false;
> >
> > if (val & HDMI_LINK_STATUS_CHANGED)
> > intel_dp_handle_hdmi_link_status_change(intel_dp);
> >
> > + if ((val & DP_TUNNELING_IRQ) &&
> > + drm_dp_tunnel_handle_irq(display->dp_tunnel_mgr,
> > + &intel_dp->aux))
> > + reprobe_needed = true;
> > +
> > return reprobe_needed;
> > }
> >
>
> --
> Cheers,
> Luca.
