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

[Lukas Wunner <lukas@wunner.de>]

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@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@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).

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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