[PATCH 07/14] drm/i915/dp: Add a separate function to reduce the link parameters

[Murthy, Arun R]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Imre
> Deak
> Sent: Monday, July 22, 2024 10:25 PM
> To: intel-gfx at lists.freedesktop.org
> Subject: [PATCH 07/14] drm/i915/dp: Add a separate function to reduce the link
> parameters
> 
> A follow-up patch will add an alternative way to reduce the link parameters in
> BW order on MST links, prepare for that here.
> 
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  .../drm/i915/display/intel_dp_link_training.c | 39 +++++++++++++++----
>  1 file changed, 31 insertions(+), 8 deletions(-)
> 
> 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 58dea87a9fa28..57536ae200b77 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -1193,6 +1193,36 @@ static int reduce_lane_count(struct intel_dp
> *intel_dp, int current_lane_count)
>  	return current_lane_count >> 1;
>  }
> 
> +static bool reduce_link_params_in_rate_lane_order(struct intel_dp *intel_dp,
> +						  const struct intel_crtc_state
> *crtc_state,
> +						  int *new_link_rate, int
> *new_lane_count) {
> +	int link_rate;
> +	int lane_count;
> +
> +	lane_count = crtc_state->lane_count;
> +	link_rate = reduce_link_rate(intel_dp, crtc_state->port_clock);
> +	if (link_rate < 0) {
> +		lane_count = reduce_lane_count(intel_dp, crtc_state-
> >lane_count);
> +		link_rate = intel_dp_max_common_rate(intel_dp);
> +	}
> +
On link training failure reducing link rate or lane count is not linear. Sometime we fall from uhbr to hbr and then again with uhbr with lane reduction. So would it be better to have a table/list for the fallback link rate/lane count.

Thanks and Regards,
Arun R Murthy
--------------------
> +	if (lane_count < 0)
> +		return false;
> +
> +	*new_link_rate = link_rate;
> +	*new_lane_count = lane_count;
> +
> +	return true;
> +}
> +
> +static bool reduce_link_params(struct intel_dp *intel_dp, const struct
> intel_crtc_state *crtc_state,
> +			       int *new_link_rate, int *new_lane_count) {
> +	return reduce_link_params_in_rate_lane_order(intel_dp, crtc_state,
> +						     new_link_rate,
> new_lane_count); }
> +
>  static int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  						   const struct intel_crtc_state
> *crtc_state)  { @@ -1206,14 +1236,7 @@ static int
> intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
>  		return 0;
>  	}
> 
> -	new_lane_count = crtc_state->lane_count;
> -	new_link_rate = reduce_link_rate(intel_dp, crtc_state->port_clock);
> -	if (new_link_rate < 0) {
> -		new_lane_count = reduce_lane_count(intel_dp, crtc_state-
> >lane_count);
> -		new_link_rate = intel_dp_max_common_rate(intel_dp);
> -	}
> -
> -	if (new_lane_count < 0)
> +	if (!reduce_link_params(intel_dp, crtc_state, &new_link_rate,
> +&new_lane_count))
>  		return -1;
> 
>  	if (intel_dp_is_edp(intel_dp) &&
> --
> 2.44.2