Re: [PATCH 4/4] drm/i915: force full detect on sink count change

[Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>]

On 9/1/2015 4:12 PM, Jani Nikula wrote:
> On Thu, 27 Aug 2015, Sivakumar Thulasimani <sivakumar.thulasimani@intel.com> wrote:
>> From: "Thulasimani,Sivakumar" <sivakumar.thulasimani@intel.com>
>>
>> This patch checks for changes in sink count between short pulse
>> hpds and forces full detect when there is a change.
>>
>> This will allow both detection of hotplug and unplug of panels
>> through dongles that give only short pulse for such events.
>>
>> v2: changed variable type from u8 to bool (Jani)
>>      return immediately if perform_full_detect is set(Siva)
> The general idea LGTM, however see below.
>
>> Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
>> ---
>>   drivers/gpu/drm/i915/intel_dp.c |   27 ++++++++++++++++++++++-----
>>   1 file changed, 22 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 834f513..279e52c 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -4370,26 +4370,39 @@ go_again:
>>    *  4. Check link status on receipt of hot-plug interrupt
>>    */
>>   static void
>> -intel_dp_check_link_status(struct intel_dp *intel_dp)
>> +intel_dp_check_link_status(struct intel_dp *intel_dp, bool *perform_full_detect)
>>   {
>>   	struct drm_device *dev = intel_dp_to_dev(intel_dp);
>>   	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
>>   	struct intel_crtc *crtc =
>>   		to_intel_crtc(dp_to_dig_port(intel_dp)->base.base.crtc);
>>   	u8 sink_irq_vector;
>> +	u8 old_sink_count = intel_dp->sink_count;
>> +	bool ret;
>>   	u8 link_status[DP_LINK_STATUS_SIZE];
>>   
>>   	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
>>   
>> +	*perform_full_detect = false;
>> +
>>   	/* Try to read receiver status if the link appears to be up */
>>   	if (!intel_dp_get_link_status(intel_dp, link_status)) {
>>   		return;
>>   	}
>>   
>> -	/* Now read the DPCD to see if it's actually running */
>> -	if (!intel_dp_get_dpcd(intel_dp)) {
>> +	/* Now read the DPCD to see if it's actually running
>> +	 * Don't return immediately if dpcd read failed,
>> +	 * if sink count was 1 and dpcd read failed we need
>> +	 * to do full detection
>> +	 */
>> +	ret = intel_dp_get_dpcd(intel_dp);
>> +
>> +	if (old_sink_count != intel_dp->sink_count)
>> +		*perform_full_detect = true;
> The point I was trying to make earlier is that how can you trust
> intel_dp->sink_count if intel_dp_get_dpcd failed? You don't know where
> it failed, and ->sink_count may or may not have changed. Maybe it has
> changed for real but you didn't have a chance to read it just yet.
>
>> +
>> +	/* No need to proceed if we are going to do full detect */
>> +	if (!ret || *perform_full_detect)
>>   		return;
>> -	}
> So if you're returning because of !ret, *perform_full_detect may be true
> or false, you don't know. I'd like the code to be explicit about what
> you want the caller to do when intel_dp_get_dpcd returns false, full
> detect or not.
>
> BR,
> Jani.
the idea i had in mind was if intel_dp_get_dpcd failed we should do a 
full detect.

my assumption here was that sink_count would be zero so it would take care
of this, but now that it seems to be a wrong assumption how about the 
following code ?
this makes it explicit that if dpcd read failed we will do full detect.

+	if ((old_sink_count != intel_dp->sink_count) || !ret)
+		*perform_full_detect = true;

+
+	/* No need to proceed if we are going to do full detect */
+	if (*perform_full_detect)
  		return;

>
>>   
>>   	if (!intel_encoder->base.crtc)
>>   		return;
>> @@ -5031,13 +5044,17 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
>>   		}
>>   
>>   		if (!intel_dp->is_mst) {
>> +			bool full_detect;
>>   			/*
>>   			 * we'll check the link status via the normal hot plug path later -
>>   			 * but for short hpds we should check it now
>>   			 */
>>   			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
>> -			intel_dp_check_link_status(intel_dp);
>> +			intel_dp_check_link_status(intel_dp, &full_detect);
>>   			drm_modeset_unlock(&dev->mode_config.connection_mutex);
>> +
>> +			if (full_detect)
>> +				goto put_power;
>>   		}
>>   	}
>>   
>> -- 
>> 1.7.9.5
>>

-- 
regards,
Sivakumar

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