[PATCH 2/4] drm/i915: Compute sink's max lane count/link BW at Hotplug

[Manasi Navare]

Jani,

Could you please review this patch? This is the patch that
calculates the max sink link rate and max sink lane count only
once at hotplug and then anytime the max lane count and common rates are requested,
the helper functions use these values.
This simplifies the fallback logic since we can go ahead and update
the max sink link rate and lane count to these fallback lower
values since link training failed so thus capping the max values
to fallback values.
This is better than defining common_rates array in intel_dp, because
its easier to update the max link rate vs going and updating and
resizing the whole array.
Also with this approach the helper functions do not change.

Regards
Manasi

On Mon, Dec 05, 2016 at 04:27:36PM -0800, Manasi Navare wrote:
> Sink's capabilities are advertised through DPCD registers and get
> updated only on hotplug. So they should be computed only once in the
> long pulse handler and saved off in intel_dp structure for the use
> later. For this reason two new fields max_sink_lane_count and
> max_sink_link_bw are added to intel_dp structure.
> 
> This also simplifies the fallback link rate/lane count logic
> to handle link training failure. In that case, the max_sink_link_bw
> and max_sink_lane_count can be reccomputed to match the fallback
> values lowering the sink capabilities due to link train failure.
> 
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c  | 10 ++++++++--
>  drivers/gpu/drm/i915/intel_drv.h |  4 ++++
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index db75bb9..434dc7d 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -156,7 +156,7 @@ static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
>  	u8 source_max, sink_max;
>  
>  	source_max = intel_dig_port->max_lanes;
> -	sink_max = drm_dp_max_lane_count(intel_dp->dpcd);
> +	sink_max = intel_dp->max_sink_lane_count;
>  
>  	return min(source_max, sink_max);
>  }
> @@ -213,7 +213,7 @@ static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
>  
>  	*sink_rates = default_rates;
>  
> -	return (intel_dp_max_link_bw(intel_dp) >> 3) + 1;
> +	return (intel_dp->max_sink_link_bw >> 3) + 1;
>  }
>  
>  static int
> @@ -4395,6 +4395,12 @@ static bool intel_digital_port_connected(struct drm_i915_private *dev_priv,
>  		      yesno(intel_dp_source_supports_hbr2(intel_dp)),
>  		      yesno(drm_dp_tps3_supported(intel_dp->dpcd)));
>  
> +	/* Set the max lane count for sink */
> +	intel_dp->max_sink_lane_count = drm_dp_max_lane_count(intel_dp->dpcd);
> +
> +	/* Set the max link BW for sink */
> +	intel_dp->max_sink_link_bw = intel_dp_max_link_bw(intel_dp);
> +
>  	intel_dp_print_rates(intel_dp);
>  
>  	intel_dp_read_desc(intel_dp);
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index fd77a3b..b6526ad 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -906,6 +906,10 @@ struct intel_dp {
>  	/* sink rates as reported by DP_SUPPORTED_LINK_RATES */
>  	uint8_t num_sink_rates;
>  	int sink_rates[DP_MAX_SUPPORTED_RATES];
> +	/* Max lane count for the sink as per DPCD registers */
> +	uint8_t max_sink_lane_count;
> +	/* Max link BW for the sink as per DPCD registers */
> +	int max_sink_link_bw;
>  	/* sink or branch descriptor */
>  	struct intel_dp_desc desc;
>  	struct drm_dp_aux aux;
> -- 
> 1.9.1
>