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

[Mika Kahola]

On Tue, 2015-12-22 at 16:53 +0100, Lukas Wunner 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).
> 
Thank you for the tip. I have missed this Thierry's patch.

Happy Holidays!
-Mika-

> 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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