Re: [PATCH] drm/i915/ddi: Avoid long delays during system suspend / eDP disabling

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

On Wed, 31 May 2017, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Wed, May 31, 2017 at 08:05:35PM +0300, Imre Deak wrote:
>> Atm disabling either DP or eDP outputs can generate a spurious short
>> pulse interrupt. The reason is that after disabling the port the source
>> will stop sending a valid stream data, while the sink expects either a
>> valid stream or the idle pattern. Since neither of this is sent the sink
>> assumes (after an arbitrary delay) that the link is lost and requests
>> for link retraining with a short pulse.
>> 
>> The spurious pulse is a real problem at least for eDP panels with long
>> power-off / power-cycle delays: as part of disabling the output we
>> disable the panel power. The subsequent spurious short pulse handling
>> will have to turn the power back on, which means the driver has to do a
>> redundant wait for the power-off and power-cycle delays. During system
>> suspend this leads to an unnecessary delay up to ~1s on systems with
>> such panels as reported by Rui.
>> 
>> To fix this put the sink to DPMS D3 state before turning off the port.
>> According to the DP spec in this state the sink should not request
>> retraining. This is also what we do already on pre-ddi platforms.
>> 
>> As an alternative I also tried configuring the port to send idle pattern
>> - which is against BSPec - and leave the port in normal mode before
>> turning off the port. Neither of these resolved the problem.
>> 
>> Cc: Zhang Rui <rui.zhang@intel.com>
>> Cc: David Weinehall <david.weinehall@linux.intel.com>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Reported-and-tested-by: Zhang Rui <rui.zhang@intel.com>
>> Signed-off-by: Imre Deak <imre.deak@intel.com>
>
> Makes sense to me.

I wonder if we should write D0 on hotplug.

BR,
Jani.


>
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
>> ---
>>  drivers/gpu/drm/i915/intel_ddi.c | 10 +++++++---
>>  1 file changed, 7 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
>> index 0914ad9..8bac628 100644
>> --- a/drivers/gpu/drm/i915/intel_ddi.c
>> +++ b/drivers/gpu/drm/i915/intel_ddi.c
>> @@ -1732,12 +1732,18 @@ static void intel_ddi_post_disable(struct intel_encoder *intel_encoder,
>>  	struct drm_i915_private *dev_priv = to_i915(encoder->dev);
>>  	enum port port = intel_ddi_get_encoder_port(intel_encoder);
>>  	struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
>> +	struct intel_dp *intel_dp = NULL;
>>  	int type = intel_encoder->type;
>>  	uint32_t val;
>>  	bool wait = false;
>>  
>>  	/* old_crtc_state and old_conn_state are NULL when called from DP_MST */
>>  
>> +	if (type == INTEL_OUTPUT_DP || type == INTEL_OUTPUT_EDP) {
>> +		intel_dp = enc_to_intel_dp(encoder);
>> +		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
>> +	}
>> +
>>  	val = I915_READ(DDI_BUF_CTL(port));
>>  	if (val & DDI_BUF_CTL_ENABLE) {
>>  		val &= ~DDI_BUF_CTL_ENABLE;
>> @@ -1753,9 +1759,7 @@ static void intel_ddi_post_disable(struct intel_encoder *intel_encoder,
>>  	if (wait)
>>  		intel_wait_ddi_buf_idle(dev_priv, port);
>>  
>> -	if (type == INTEL_OUTPUT_DP || type == INTEL_OUTPUT_EDP) {
>> -		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>> -		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
>> +	if (intel_dp) {
>>  		intel_edp_panel_vdd_on(intel_dp);
>>  		intel_edp_panel_off(intel_dp);
>>  	}
>> -- 
>> 2.7.4

-- 
Jani Nikula, Intel Open Source Technology Center
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