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

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

On Tue, 01 Sep 2015, Sivakumar Thulasimani <sivakumar.thulasimani@intel.com> wrote:
> 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;

Ok by me.

Jani.



>
>>
>>>   
>>>   	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
>

-- 
Jani Nikula, Intel Open Source Technology Center
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