Re: [PATCH v2 14/21] drm/i915/dp: Disable link retraining after the last fallback step

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, May 20, 2024 at 09:58:12PM +0300, Imre Deak wrote:
> After a link training failure if the link parameters can't be further
> reduced, there is no point in trying to retrain the link in the driver.
> This avoids excessive retrain attempts after detecting a bad link, for
> instance while handling MST HPD IRQs, which is likely redundant as the
> link training failed already twice with the same minimum link
> parameters. Userspace can still try to retrain the link with these
> parameters via a modeset.
> 
> While at it make the error message more accurate and emit instead a
> debug message if the link training failure was only forced for testing
> purposes.
> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  .../drm/i915/display/intel_display_types.h    |  1 +
>  drivers/gpu/drm/i915/display/intel_dp.c       |  4 ++++
>  .../drm/i915/display/intel_dp_link_training.c | 22 +++++++++++++------
>  3 files changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index bde518c843468..eb0cac3e27acf 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1765,6 +1765,7 @@ struct intel_dp {
>  		int max_lane_count;
>  		/* Max rate for the current link */
>  		int max_rate;
> +		bool retrain_disabled;
>  		/* Sequential link training failures after a passing LT */
>  		int seq_train_failures;
>  	} link;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index b72dbd7becb74..34d64fe3302ef 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2950,6 +2950,7 @@ static void intel_dp_reset_link_params(struct intel_dp *intel_dp)
>  {
>  	intel_dp->link.max_lane_count = intel_dp_max_common_lane_count(intel_dp);
>  	intel_dp->link.max_rate = intel_dp_max_common_rate(intel_dp);
> +	intel_dp->link.retrain_disabled = false;
>  	intel_dp->link.seq_train_failures = 0;
>  }
>  
> @@ -5061,6 +5062,9 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
>  					intel_dp->lane_count))
>  		return false;
>  
> +	if (intel_dp->link.retrain_disabled)
> +		return false;
> +
>  	if (intel_dp->link.seq_train_failures)
>  		return true;
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> index 97d499e4b6ef7..375f59afd4dec 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -1165,10 +1165,8 @@ static int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  		new_link_rate = intel_dp_max_common_rate(intel_dp);
>  	}
>  
> -	if (new_lane_count < 0) {
> -		drm_err(&i915->drm, "Link Training Unsuccessful\n");
> +	if (new_lane_count < 0)
>  		return -1;
> -	}
>  
>  	if (intel_dp_is_edp(intel_dp) &&
>  	    !intel_dp_can_link_train_fallback_for_edp(intel_dp, new_link_rate, new_lane_count)) {
> @@ -1187,7 +1185,7 @@ static int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  	return 0;
>  }
>  
> -static void intel_dp_schedule_fallback_link_training(struct intel_atomic_state *state,
> +static bool intel_dp_schedule_fallback_link_training(struct intel_atomic_state *state,
>  						     struct intel_dp *intel_dp,
>  						     const struct intel_crtc_state *crtc_state)
>  {
> @@ -1195,7 +1193,7 @@ static void intel_dp_schedule_fallback_link_training(struct intel_atomic_state *
>  
>  	if (!intel_digital_port_connected(&dp_to_dig_port(intel_dp)->base)) {
>  		lt_dbg(intel_dp, DP_PHY_DPRX, "Link Training failed on disconnected sink.\n");
> -		return;
> +		return true;
>  	}
>  
>  	if (intel_dp->hobl_active) {
> @@ -1203,11 +1201,13 @@ static void intel_dp_schedule_fallback_link_training(struct intel_atomic_state *
>  		       "Link Training failed with HOBL active, not enabling it from now on\n");
>  		intel_dp->hobl_failed = true;
>  	} else if (intel_dp_get_link_train_fallback_values(intel_dp, crtc_state)) {
> -		return;
> +		return false;
>  	}
>  
>  	/* Schedule a Hotplug Uevent to userspace to start modeset */
>  	intel_dp_queue_modeset_retry_for_link(state, encoder, crtc_state);
> +
> +	return true;
>  }
>  
>  /* Perform the link training on all LTTPRs and the DPRX on a link. */
> @@ -1518,7 +1518,15 @@ void intel_dp_start_link_train(struct intel_atomic_state *state,
>  		return;
>  	}
>  
> -	intel_dp_schedule_fallback_link_training(state, intel_dp, crtc_state);
> +	if (intel_dp_schedule_fallback_link_training(state, intel_dp, crtc_state))
> +		return;
> +
> +	intel_dp->link.retrain_disabled = true;
> +
> +	if (!passed)
> +		lt_err(intel_dp, DP_PHY_DPRX, "Can't reduce link training parameters after failure\n");
> +	else
> +		lt_dbg(intel_dp, DP_PHY_DPRX, "Can't reduce link training parameters after forced failure\n");

The forced failure stuff is in later patch, is it not?

>  }
>  
>  void intel_dp_128b132b_sdp_crc16(struct intel_dp *intel_dp,
> -- 
> 2.43.3

-- 
Ville Syrjälä
Intel