Re: [PATCH 11/20] drm/i915/dp: Reprobe connector if getting/acking device IRQs fails

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

On Thu, Jun 26, 2025 at 01:46:27PM +0300, Jani Nikula wrote:
> On Thu, 26 Jun 2025, Imre Deak <imre.deak@intel.com> wrote:
> > On Thu, Jun 26, 2025 at 01:23:12PM +0300, Jani Nikula wrote:
> >> On Thu, 26 Jun 2025, Imre Deak <imre.deak@intel.com> wrote:
> >> > On Thu, Jun 26, 2025 at 12:12:11PM +0300, Jani Nikula wrote:
> >> >> On Thu, 26 Jun 2025, Imre Deak <imre.deak@intel.com> wrote:
> >> >> > From: Imre Deak <imre.deak@gmail.com>
> >> >> >
> >> >> > An AUX access failure during HPD IRQ handling should be handled by
> >> >> > falling back to a full connector detection, ensure that if the failure
> >> >> > happens while reading/acking a device service IRQ.
> >> >> >
> >> >> > Signed-off-by: Imre Deak <imre.deak@gmail.com>
> >> >> > ---
> >> >> >  drivers/gpu/drm/i915/display/intel_dp.c | 21 +++++++++++++++------
> >> >> >  1 file changed, 15 insertions(+), 6 deletions(-)
> >> >> >
> >> >> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> >> >> > index 7793a72983abd..7eb208d2c321b 100644
> >> >> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> >> >> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> >> >> > @@ -5393,16 +5393,20 @@ void intel_dp_check_link_state(struct intel_dp *intel_dp)
> >> >> >  	intel_encoder_link_check_queue_work(encoder, 0);
> >> >> >  }
> >> >> >  
> >> >> > -static void intel_dp_check_device_service_irq(struct intel_dp *intel_dp)
> >> >> > +static bool intel_dp_check_device_service_irq(struct intel_dp *intel_dp)
> >> >> 
> >> >> I don't think "check" is very intuitive in function names. Check
> >> >> something, but then what? Is it like an assert or does it do something
> >> >> active or what?
> >> >> 
> >> >> What does a boolean return from a check function mean?
> >> >> 
> >> >> It's not obvious to the reader at all.
> >> >
> >> > I agree, but in this patch I didn't want to change the function name.
> >> 
> >> Arguably adding a return value changes the meaning already...
> >> 
> >> >
> >> >> 
> >> >> >  {
> >> >> >  	struct intel_display *display = to_intel_display(intel_dp);
> >> >> >  	u8 val;
> >> >> >  
> >> >> >  	if (drm_dp_dpcd_readb(&intel_dp->aux,
> >> >> > -			      DP_DEVICE_SERVICE_IRQ_VECTOR, &val) != 1 || !val)
> >> >> > -		return;
> >> >> > +			      DP_DEVICE_SERVICE_IRQ_VECTOR, &val) != 1)
> >> >> > +		return true;
> >> >> 
> >> >> Looks like true means the check failed... while usually true for boolean
> >> >> functions means success.
> >> >
> >> > The function returns true as before if a full connector detection is needed.
> >> 
> >> But it didn't return anything before! And that meaning is not conveyed
> >> to the reader in *any* reasonable way!
> >
> > This function is the counterpart of intel_dp_check_link_service_irq()
> > both functions having the same purpose, reading and handling HPD IRQs.
> > The latter one's return value is true if a reprobe is needed and this
> > patch doesn't change that, it keeps the two functions behave the same
> > way.
> >
> >> The absolute minimum is to add a comment (mind you, kernel-doc is
> >> overkill) stating what the return value means.
> >
> > The function name will change in a follow-up patch and I think that
> > doesn't require a comment on the return value.
> >
> >> >> 
> >> >> >  
> >> >> > -	drm_dp_dpcd_writeb(&intel_dp->aux, DP_DEVICE_SERVICE_IRQ_VECTOR, val);
> >> >> > +	if (!val)
> >> >> > +		return false;
> >> >> > +
> >> >> > +	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_DEVICE_SERVICE_IRQ_VECTOR, val) != 1)
> >> >> > +		return true;
> >> >> >  
> >> >> >  	if (val & DP_AUTOMATED_TEST_REQUEST)
> >> >> >  		intel_dp_test_request(intel_dp);
> >> >> 
> >> >> Whoa, it's not a *check* function at all?! It actually *handles* the
> >> >> service irqs.
> >> >> 
> >> >> Can we rephrase the function name?
> >> >
> >> > I want to keep the function name in this patch. In the following patches
> >> > I will separate this part and rename it to
> >> > intel_dp_get_and_ack_device_service_irq(). 
> >> 
> >> Right, saw that now. But even for that function name the meaning of the
> >> return value is ambiguous.
> >
> > All the get/ack IRQ functions in intel_dp.c return true for success.
> 
> Argh. You just said it doesn't mean success/failure, it means if full
> connector detection is needed?!

intel_dp_check_device_service_irq(),
intel_dp_check_link_service_irq() -> return value indicates if a
connector detection is needed.

intel_dp_get_and_ack_device_service_irq(),
intel_dp_get_and_ack_link_service_irq() -> return value indicates if
getting/acking the IRQ succeeded,s imilarly to
intel_dp_get_sink_irq_esi(), intel_dp_ack_sink_irq_esi().

> BR,
> Jani
> 
> 
> >
> >> 
> >> BR,
> >> Jani.
> >> 
> >> >
> >> >
> >> >> int intel_dp_handle_device_service_irq() and int returns maybe?
> >> >> BR,
> >> >> Jani.
> >> >> 
> >> >> > @@ -5412,6 +5416,8 @@ static void intel_dp_check_device_service_irq(struct intel_dp *intel_dp)
> >> >> >  
> >> >> >  	if (val & DP_SINK_SPECIFIC_IRQ)
> >> >> >  		drm_dbg_kms(display->drm, "Sink specific irq unhandled\n");
> >> >> > +
> >> >> > +	return false;
> >> >> >  }
> >> >> >  
> >> >> >  static bool intel_dp_check_link_service_irq(struct intel_dp *intel_dp)
> >> >> > @@ -5476,8 +5482,11 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
> >> >> >  		/* No need to proceed if we are going to do full detect */
> >> >> >  		return false;
> >> >> >  
> >> >> > -	intel_dp_check_device_service_irq(intel_dp);
> >> >> > -	reprobe_needed = intel_dp_check_link_service_irq(intel_dp);
> >> >> > +	if (intel_dp_check_device_service_irq(intel_dp))
> >> >> > +		reprobe_needed = true;
> >> >> > +
> >> >> > +	if (intel_dp_check_link_service_irq(intel_dp))
> >> >> > +		reprobe_needed = true;
> >> >> >  
> >> >> >  	/* Handle CEC interrupts, if any */
> >> >> >  	drm_dp_cec_irq(&intel_dp->aux);
> >> >> 
> >> >> -- 
> >> >> Jani Nikula, Intel
> >> 
> >> -- 
> >> Jani Nikula, Intel
> 
> -- 
> Jani Nikula, Intel