Re: [PATCH 13/17] drm/i915: Update intel_dp_hpd_pulse() to check link status for non-MST operation

[Todd Previte <tprevite@gmail.com>]

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On 12/17/14 10:57 AM, Paulo Zanoni wrote:
> 2014-12-10 21:53 GMT-02:00 Todd Previte<tprevite@gmail.com>:
>> Moves the non-MST case out of the if-statement and places it at the beginning
>> of the function to handle HPD events for SST mode. The reasoning behind this
>> is to accommodate link status checks for compliance testing. Some test devices
>> use long pulses to perform test requests so link status must be checked
>> regardless of the pulse width for the SST operational mode.
> Can you please elaborate a little more on what do you see on these
> devices? The test spec is very clear about short vs long HPD pulses,
> so it's hard to believe a test device would get this wrong. We have
> some registers on the PCH that allow us to redefine short vs long
> durations. Have you tried to play with them?
>
> More below:
The issue is not in differentiating between the two pulse widths. The 
problem is that compliance testing mixes the two together, i.e. some 
tests are IRQ events where the source has to "service" the sink while 
other tests are examining the hot plug detection and response 
functionality. So when it comes to compliance testing, they both have to 
be handled and checked to see if there's a test request coming in or if 
it's a real HPD event of some kind. The current implementation only 
checks SST mode for the short pulse case.

In light of Daniel's comment, though, that makes this code even more 
broken. The best place to handle this (as I mention in my response to 
Daniel) is to place the SST case after the mst_fail tag. That way, once 
it is determined that MST mode is not in use, the SST handler can be 
invoked and events responded to appropriately.


>> 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.
>>
>> Signed-off-by: Todd Previte<tprevite@gmail.com>
>> ---
>>   drivers/gpu/drm/i915/intel_dp.c | 22 ++++++++++++----------
>>   1 file changed, 12 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 4a55ca6..73014d8 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -4613,6 +4613,18 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
>>          power_domain = intel_display_port_power_domain(intel_encoder);
>>          intel_display_power_get(dev_priv, power_domain);
>>
>> +       if (!intel_dp->is_mst) {
>> +               /*
>> +                *  Pulse width doesn't matter for SST mode
>> +                *  Handle the HPD event now
>> +               */
>> +               drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
>> +               intel_dp_check_link_status(intel_dp);
> The very first thing intel_dp_check_link_status() does is to return in
> case "connector->base.status != connected". If we're getting a long
> HPD, it doesn't seem make sense to check this field because the status
> might be changing due to the long HPD.
Long pulses are either connect OR disconnect events. In the case of the 
test device, what happens is that it's already connected, so HPD is 
asserted. It pulses the HPD line low for > 2ms and then reasserts it 
sometime later once the source device has disabled the main link. So it 
becomes a 2-fold event for us - the initial connected->disconnected 
transition and the following disconnected->connected transition. Both of 
those invoke our IRQ handler and cause neat and exciting things to 
happen. For compliance testing, the disconnect event needs to be ignored 
(by the test code, anyways) and the connect event needs to be checked 
for TEST_REQUEST=1. Thus, it absolutely makes sense to check this here.

>> +               drm_modeset_unlock(&dev->mode_config.connection_mutex);
>> +               ret = false;
>> +               goto put_power;
>> +       }
>> +
>>          if (long_hpd) {
>>
>>                  if (HAS_PCH_SPLIT(dev)) {
>> @@ -4637,16 +4649,6 @@ 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 = false;
>>          goto put_power;
>> --
>> 1.9.1
>>
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>> Intel-gfx@lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>


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