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

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

On 9/2/2015 2:43 PM, Daniel Vetter wrote:
> On Thu, Aug 27, 2015 at 02:18:32PM +0530, Sivakumar Thulasimani 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)
>>
>> Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
> That's still incomplete since in the hotplug work function we check
> whether ->detect status has changed. If that doesn't happen (e.g. sink
> count changes from 1->2 or whatever) then we'll fail to generate the
> required uevent.
>
> I suspect the only clean way to fix this is to merge all the dp hpd
> handling together into one place and stop using ->detect for some parts of
> it. Then we would have one place only that decides whether anything
> changed, and whether we need to send anything to userspace or not.
> -Daniel
i doubt sink count change from 1->2 is valid.
1)  we support only edp and SST displays in intel_dp_detect.
we should handle all mst related code in intel_dp_hpd_pulse.
2) check_link_status is called from withing !mst check so i dont see it 
change from 1 to 2.
3) even if it changes from 1 to 2, for the given port without mst there 
is no way to
switch between first sink to second one outside mst logic.

correct me if i am wrong, the only reason to call intel_dp_detect is to 
see if
"one display is connected or disconnected" which i feel is fine with 
current code.

But i do agree that we need to clean up intel_dp_hpd_pulse since it does 
a lot of things
then repeats those same operations in intel_dp_detect. for example we 
read dpcd 0-14,
link status and probe oui only to repeat the same steps in the 
intel_dp_detect. considering
that our dpcd read has 1ms delay this can add up pretty quick.

if the intention of intel_dp_hpd_pulse is to handle mst displays, that 
should be checked first
and continue only if display is mst otherwise we should just jump to 
intel_dp_detect.
>> ---
>>   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;
>> +
>> +	/* No need to proceed if we are going to do full detect */
>> +	if (!ret || *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
>>
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>> Intel-gfx@lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
regards,
Sivakumar

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