Re: [PATCH] drm/i915: Update intel_dp_hpd_pulse() to check link status for non-MST operation

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On 03/06/2015 08:34 AM, Daniel Vetter wrote:
> On Thu, Mar 05, 2015 at 11:22:19AM -0700, Todd Previte wrote:
>> Update the hot plug function to handle the SST case. Instead of placing
>> the SST case within the long/short pulse block, it is now handled after
>> determining that MST mode is not in use. This way, the topology management
>> layer can handle any MST-related operations while SST operations are still
>> correctly handled afterwards.
>>
>> This patch also corrects the problem of SST mode only being handled in the
>> case of a short (0.5ms - 1.0ms) HPD pulse. For compliance testing purposes
>> both short and long pulses are used by the different tests, thus both cases
>> need to be addressed for SST.
>>
>> This patch replaces [PATCH 10/10] drm/i915: Fix intel_dp_hot_plug() in the
>> previous compliance testing patch sequence. Review feedback on that patch
>> indicated that updating intel_dp_hot_plug() was not the correct place for
>> the test handler.
>>
>> For the SST case, the main stream is disabled for long HPD pulses as this
>> generally indicates either a connect/disconnect event or link failure. For
>> a number of case in compliance testing, the source is required to disable
>> the main link upon detection of a long HPD.
>>
>> V2:
>> - N/A
>> V3:
>> - Place the SST mode link status check into the mst_fail case
>> - Remove obsolete comment regarding SST mode operation
>> - Removed an erroneous line of code that snuck in during rebasing
>> V4:
>> - Added a disable of the main stream (DP transport) for the long pulse case
>>   for SST to support compliance testing
>>
>> Signed-off-by: Todd PRevite <tprevite@gmail.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c | 25 +++++++++++++++----------
>>  1 file changed, 15 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 080cc23..2460d14 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -4618,16 +4618,6 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
>>  			if (intel_dp_check_mst_status(intel_dp) == -EINVAL)
>>  				goto mst_fail;
>>  		}
>> -
>> -		if (!intel_dp->is_mst) {
>> -			/*
>> -			 * 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);
>> -			drm_modeset_unlock(&dev->mode_config.connection_mutex);
>> -		}
>>  	}
>>  
>>  	ret = IRQ_HANDLED;
>> @@ -4639,6 +4629,21 @@ mst_fail:
>>  		DRM_DEBUG_KMS("MST device may have disappeared %d vs %d\n", intel_dp->is_mst, intel_dp->mst_mgr.mst_state);
>>  		intel_dp->is_mst = false;
>>  		drm_dp_mst_topology_mgr_set_mst(&intel_dp->mst_mgr, intel_dp->is_mst);
>> +	} else {
>> +		/* SST mode - handle short/long pulses here */
>> +		drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
>> +		/* Clear compliance testing flags/data here to prevent
>> +		 * false detection in userspace */
>> +		intel_dp->compliance_test_data = 0;
>> +		intel_dp->compliance_testing_active = 0;
>> +		/* For a long pulse in SST mode, disable the main link */
>> +		if (long_hpd) {
>> +			I915_WRITE(DP_TP_CTL(intel_dig_port->port),
>> +					      ~DP_TP_CTL_ENABLE);
>> +		}
> 
> Disabling the  main link should be done in userspace. All long pulse
> requests should be forwarded to userspace as a hotplug event. Userspace
> can then react to that hotplug appropriately. This way we can again
> exercise the normal operation of all our dp code.

What's your concern here?  Do you want to make sure we get coverage on
dp_link_down()?  It looks like that might be safe to use here instead of
flipping the disable bit directly.  Or did you want to go through the
whole pipe/port shutdown sequence as well?  If so, I think the dpms
tests will already cover that, separate from simple compliance.

Jesse
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