Re: [Intel-gfx] [PATCH] drm/i915/dp: Reset link params on connector disconnect

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

On Wed, Jun 03, 2020 at 05:23:59PM -0700, Manasi Navare wrote:
> We have noticed that when link training fails the panel
> sends a long pulse indicating connector disconnect. In this case
> we need to reset the link parameters instead of continuing
> to use the fallback parameters since else this long pulse
> by the panel followed by a modeset request which was triggered by the userspace
> before getting the connector status as disconnected, will
> result into a modeset now using lower link rate/lane count values.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1385
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 28 +++++++++++++++++--------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 55fda074c0ad..f7af372647dd 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -6111,6 +6111,18 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
>  	intel_dp->edid_quirks = 0;
>  }
>  
> +static void
> +intel_dp_reset_link_params(struct intel_dp *intel_dp)
> +{
> +	/* Initial max link lane count */
> +	intel_dp->max_link_lane_count = intel_dp_max_common_lane_count(intel_dp);
> +
> +	/* Initial max link rate */
> +	intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
> +
> +	intel_dp->reset_link_params = false;
> +}
> +
>  static int
>  intel_dp_detect(struct drm_connector *connector,
>  		struct drm_modeset_acquire_ctx *ctx,
> @@ -6139,6 +6151,11 @@ intel_dp_detect(struct drm_connector *connector,
>  		memset(&intel_dp->compliance, 0, sizeof(intel_dp->compliance));
>  		memset(intel_dp->dsc_dpcd, 0, sizeof(intel_dp->dsc_dpcd));
>  
> +		/*Reset the immutable VRR Capable property */
> +		drm_connector_set_vrr_capable_property(connector,
> +						       false);
> +		intel_dp_reset_link_params(intel_dp);
> +

Why would we care what those are when the sink is disconnected?

>  		if (intel_dp->is_mst) {
>  			drm_dbg_kms(&dev_priv->drm,
>  				    "MST device may have disappeared %d vs %d\n",
> @@ -6152,15 +6169,8 @@ intel_dp_detect(struct drm_connector *connector,
>  		goto out;
>  	}
>  
> -	if (intel_dp->reset_link_params) {
> -		/* Initial max link lane count */
> -		intel_dp->max_link_lane_count = intel_dp_max_common_lane_count(intel_dp);
> -
> -		/* Initial max link rate */
> -		intel_dp->max_link_rate = intel_dp_max_common_rate(intel_dp);
> -
> -		intel_dp->reset_link_params = false;
> -	}
> +	if (intel_dp->reset_link_params)
> +		intel_dp_reset_link_params(intel_dp);
>  
>  	intel_dp_print_rates(intel_dp);
>  
> -- 
> 2.19.1

-- 
Ville Syrjälä
Intel
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