[Intel-gfx] [PATCH v5 2/2] drm/i915: Check DP no aux transaction bit on link training

[Jani Nikula]

On Tue, 22 Dec 2015, Lukas Wunner <lukas at wunner.de> wrote:
> Hi Mika,
>
> On Mon, Dec 21, 2015 at 01:39:15PM +0200, Mika Kahola wrote:
>> Check if no AUX transactions are required on DP link training.
>> If this bit is set, we can reuse the known good drive current
>> and pre-emphasis level from the last "full" link training.
>> 
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91393
>> Signed-off-by: Mika Kahola <mika.kahola at intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_dp.c               |  2 +-
>>  drivers/gpu/drm/i915/intel_dp_link_training.c | 19 +++++++++++++++++++
>>  drivers/gpu/drm/i915/intel_drv.h              |  1 +
>>  3 files changed, 21 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index 6b36d82..3137187 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -3852,7 +3852,7 @@ intel_dp_link_down(struct intel_dp *intel_dp)
>>  	intel_dp->DP = DP;
>>  }
>>  
>> -static bool
>> +bool
>>  intel_dp_get_dpcd(struct intel_dp *intel_dp)
>>  {
>>  	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
>> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
>> index 59d59be..5fb3f97 100644
>> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
>> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
>> @@ -85,6 +85,25 @@ static bool
>>  intel_dp_reset_link_train(struct intel_dp *intel_dp,
>>  			uint8_t dp_train_pat)
>>  {
>> +	bool has_dpcd;
>> +	bool no_aux_handshake = false;
>> +
>> +	has_dpcd = intel_dp_get_dpcd(intel_dp);
>> +
>> +	/*
>> +	 * Source device can try to use drive current and pre-emphasis
>> +	 * parameters computed by the last "full" link training if the
>> +	 * DP_NO_AUX_HANDSHAKE_LINK_TRAINING bit is set to 1.
>> +	 */
>> +	if (has_dpcd) {
>> +		if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11) {
>> +			no_aux_handshake = (intel_dp->dpcd[DP_MAX_DOWNSPREAD] &
>> +					    DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
>> +		}
>> +	}
>> +
>> +	intel_dp->train_set_valid &= no_aux_handshake;
>> +
>
> If Thierry Reding's patches get merged (posted to dri-devel@ on Dec 14
> with <1450097764-30063-1-git-send-email-thierry.reding at gmail.com>),
> you could just use
>
> 	if (has_dpcd && drm_dp_fast_training_cap(intel_dp->dpcd))
> 		intel_dp->train_set_valid &= true;
>
> Also, if the patches get merged, the no_aux_handshake attribute in dev_priv
> can be dropped (set in intel_edp_init_connector() but never read).

Good points, but we don't generally write code, let alone bugfixes, on
top of code that hasn't been merged.

BR,
Jani.


>
> Best regards,
>
> Lukas
>
>>  	DRM_DEBUG_KMS("link training optimization: %s\n",
>>  		      intel_dp->train_set_valid ? "true" : "false");
>>  
>> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
>> index d523ebb..c36a70c 100644
>> --- a/drivers/gpu/drm/i915/intel_drv.h
>> +++ b/drivers/gpu/drm/i915/intel_drv.h
>> @@ -1239,6 +1239,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc);
>>  bool intel_dp_compute_config(struct intel_encoder *encoder,
>>  			     struct intel_crtc_state *pipe_config);
>>  bool intel_dp_is_edp(struct drm_device *dev, enum port port);
>> +bool intel_dp_get_dpcd(struct intel_dp *intel_dp);
>>  enum irqreturn intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port,
>>  				  bool long_hpd);
>>  void intel_edp_backlight_on(struct intel_dp *intel_dp);
>> -- 
>> 1.9.1
>> 
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-- 
Jani Nikula, Intel Open Source Technology Center