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

[Jani Nikula <jani.nikula@linux.intel.com>]

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?!

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