[Intel-gfx] [PATCH v5 1/3] drm/i915: Disable fast link training if DP config changes

[Ville Syrjälä]

On Mon, Jan 04, 2016 at 01:21:22PM +0200, Mika Kahola wrote:
> Disable DP link training optimization if DP link configuration
> changes. If one of the DP link parameters i.e. link rate or
> lane count changes the link training does no longer apply the
> previously computed drive current and pre-emphasis level.
> Instead, the link training is started with zero values.
> 
> v5: Commit message update. Split the original patch in two.
>     This part considers only changes on link configuration.
>     Removed unnecessary debug messages. (Ville)
> 
> v4: Parameter and debug message naming improvements.
>     Fix for link parameter check (Ville)
> 
> v3: Remove cached old link parameters. Instead, disable
>     fast link training feature when link parameters are
>     set (Ville)
> 
> v2: Readout DPCD register to check if no aux handshaking is
>     required in link training (Ander)
> 
> 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               | 5 +++++
>  drivers/gpu/drm/i915/intel_dp_link_training.c | 3 +++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 796e3d3..6b36d82 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -1676,6 +1676,11 @@ found:
>  void intel_dp_set_link_params(struct intel_dp *intel_dp,
>  			      const struct intel_crtc_state *pipe_config)
>  {
> +	if (intel_dp->link_rate != pipe_config->port_clock ||
> +	    intel_dp->lane_count != pipe_config->lane_count) {
> +		intel_dp->train_set_valid = false;
> +	}
> +
>  	intel_dp->link_rate = pipe_config->port_clock;
>  	intel_dp->lane_count = pipe_config->lane_count;
>  }
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 8888793..59d59be 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -85,6 +85,9 @@ static bool
>  intel_dp_reset_link_train(struct intel_dp *intel_dp,
>  			uint8_t dp_train_pat)
>  {
> +	DRM_DEBUG_KMS("link training optimization: %s\n",
> +		      intel_dp->train_set_valid ? "true" : "false");

yesno(intel_dp->train_set_valid)

With that
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

> +
>  	if (!intel_dp->train_set_valid)
>  		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
>  	intel_dp_set_signal_levels(intel_dp);
> -- 
> 1.9.1

-- 
Ville Syrjälä
Intel OTC