Re: [PATCH 10/16] drm/i915/dp_mst: Rework pipe joiner logic in compute_config

[Imre Deak <imre.deak@intel.com>]

On Thu, Jan 29, 2026 at 10:41:48PM +0530, Ankit Nautiyal wrote:
> Similar to the DP SST, refactor mst_stream_compute_config() to iterate
> over joiner candidates and select the minimal joiner configuration that
> satisfies the mode requirements. This prepares the logic for future changes
> that will consider DSC slice overhead.
> 
> v2:
>  - Move the check for dotclock in the new helper and check for both DSC and
>    non-DSC case. In case the check fails for non-DSC, fallback to DSC
>    configuration. (Imre)
>  - Propagate the return value from the core helper:
>    mst_stream_compute_link_for_joined_pipes(). (Imre)
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 46 ++++++++++++++++-----
>  1 file changed, 35 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 55b2ccb45e43..c0d854b107b5 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -602,12 +602,16 @@ static int mst_stream_compute_link_for_joined_pipes(struct intel_encoder *encode
>  {
>  	struct intel_display *display = to_intel_display(encoder);
>  	struct intel_dp *intel_dp = to_primary_dp(encoder);
> +	const struct drm_display_mode *adjusted_mode =
> +		&pipe_config->hw.adjusted_mode;
>  	struct intel_connector *connector =
>  		to_intel_connector(conn_state->connector);
> +	int max_dotclk = display->cdclk.max_dotclk_freq;
>  	struct link_config_limits limits;
>  	bool dsc_needed, joiner_needs_dsc;
>  	int ret = 0;
>  
> +	max_dotclk *= num_joined_pipes;
>  	joiner_needs_dsc = intel_dp_joiner_needs_dsc(display, num_joined_pipes);
>  
>  	dsc_needed = joiner_needs_dsc || intel_dp->force_dsc_en ||
> @@ -621,7 +625,7 @@ static int mst_stream_compute_link_for_joined_pipes(struct intel_encoder *encode
>  		if (ret == -EDEADLK)
>  			return ret;
>  
> -		if (ret)
> +		if (ret || adjusted_mode->clock > max_dotclk)
>  			dsc_needed = true;
>  	}
>  
> @@ -664,6 +668,9 @@ static int mst_stream_compute_link_for_joined_pipes(struct intel_encoder *encode
>  						  pipe_config->dp_m_n.tu);
>  		if (ret)
>  			return ret;
> +
> +		if (adjusted_mode->clock > max_dotclk)
> +			return -EINVAL;
>  	}
>  
>  	if (ret)
> @@ -689,7 +696,8 @@ static int mst_stream_compute_config(struct intel_encoder *encoder,
>  	const struct drm_display_mode *adjusted_mode =
>  		&pipe_config->hw.adjusted_mode;
>  	int num_joined_pipes;
> -	int ret = 0;
> +	int num_pipes;
> +	int ret = -EINVAL;
>  
>  	if (pipe_config->fec_enable &&
>  	    !intel_dp_supports_fec(intel_dp, connector, pipe_config))
> @@ -702,16 +710,32 @@ static int mst_stream_compute_config(struct intel_encoder *encoder,
>  	pipe_config->output_format = INTEL_OUTPUT_FORMAT_RGB;
>  	pipe_config->has_pch_encoder = false;
>  
> -	num_joined_pipes = intel_dp_num_joined_pipes(intel_dp, connector,
> -						     adjusted_mode->crtc_hdisplay,
> -						     adjusted_mode->crtc_clock);
> -	if (num_joined_pipes > 1)
> -		pipe_config->joiner_pipes = GENMASK(crtc->pipe + num_joined_pipes - 1, crtc->pipe);
> +	for (num_pipes = 1; num_pipes <= I915_MAX_PIPES; num_pipes++) {
> +		if (connector->force_joined_pipes &&
> +		    num_pipes != connector->force_joined_pipes)
> +			continue;
> +
> +		num_joined_pipes = num_pipes;

No need for two variables, fixing that:
Reviewed-by: Imre Deak <imre.deak@intel.com>

> +
> +		if (!intel_dp_can_join(display, num_joined_pipes))
> +			continue;
> +
> +		if (adjusted_mode->hdisplay >
> +		    num_joined_pipes * intel_dp_max_hdisplay_per_pipe(display))
> +			continue;
> +
> +		if (num_joined_pipes > 1)
> +			pipe_config->joiner_pipes = GENMASK(crtc->pipe + num_joined_pipes - 1,
> +							    crtc->pipe);
> +
> +		ret = mst_stream_compute_link_for_joined_pipes(encoder,
> +							       pipe_config,
> +							       conn_state,
> +							       num_joined_pipes);
> +		if (!ret)
> +			break;
> +	}
>  
> -	ret = mst_stream_compute_link_for_joined_pipes(encoder,
> -						       pipe_config,
> -						       conn_state,
> -						       num_joined_pipes);
>  	if (ret)
>  		return ret;
>  
> -- 
> 2.45.2
>