Re: [PATCH 2/2] drm/i915/dp: Clamp the connector max_bpc request to the valid pipe bpp range

["Michał Grzelak" <michal.grzelak@intel.com>]

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On Wed, 11 Feb 2026, Imre Deak wrote:
> The user's request for a maximum BPC - via the max-bpc connector
> property - determines the pipe BPP selected by the encoder, which is in
> turn used either as the uncompressed output BPP or as the input BPP for
> the DSC engine. This user-requested BPC->BPP can be outside of the
> source/sink's supported valid min/max pipe BPP range and atm such an
> out-of-bound request will be rejected by the encoder's state
> computation.
>
> As opposed to the above, the semantic for the max-bpc connector property

s/semantic/semantics

> - which the user may reasonably expect - is not to fail the modeset in
> case of an out-of-bound max BPC request, rather to adjust the request
> clamping it to the valid BPP range.
>
> Based on the above, calculate the baseline (i.e. the non-DP specific
> platform/EDID) _maximum_ pipe BPP, storing it in
> intel_crtc_state::max_pipe_bpp, separately from the baseline _target_
> pipe BPP (which is the lower BPP of the baseline maximum and requested
> BPP, stored in intel_crtc_state::pipe_bpp). This allows the encoder
> state computation to use the baseline maximum pipe BPP as a hard limit
> for the selected pipe BPP, while also letting it use the baseline target
> pipe BPP only as a preference, clamping this target BPP to the valid
> DP pipe BPP range.
>
> Signed-off-by: Imre Deak <imre.deak@intel.com>

Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>

BR,
Michał

> ---
> drivers/gpu/drm/i915/display/intel_display.c  | 12 ++++++++++
> .../drm/i915/display/intel_display_types.h    |  1 +
> drivers/gpu/drm/i915/display/intel_dp.c       | 24 +++++++++++++++++--
> 3 files changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index ab4b59916d2e7..dae7a7d11cb84 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -4374,12 +4374,24 @@ compute_sink_pipe_bpp(const struct drm_connector_state *conn_state,
> 	struct intel_display *display = to_intel_display(crtc_state);
> 	struct drm_connector *connector = conn_state->connector;
> 	const struct drm_display_info *info = &connector->display_info;
> +	int edid_bpc = info->bpc ? : 8;
> 	int target_pipe_bpp;
> +	int max_edid_bpp;
> +
> +	max_edid_bpp = bpc_to_bpp(edid_bpc);
> +	if (max_edid_bpp < 0)
> +		return max_edid_bpp;
>
> 	target_pipe_bpp = bpc_to_bpp(conn_state->max_bpc);
> 	if (target_pipe_bpp < 0)
> 		return target_pipe_bpp;
>
> +	/*
> +	 * The maximum pipe BPP is the minimum of the max platform BPP and
> +	 * the max EDID BPP.
> +	 */
> +	crtc_state->max_pipe_bpp = min(crtc_state->pipe_bpp, max_edid_bpp);
> +
> 	if (target_pipe_bpp < crtc_state->pipe_bpp) {
> 		drm_dbg_kms(display->drm,
> 			    "[CONNECTOR:%d:%s] Limiting target display pipe bpp to %d "
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index e6298279dc892..e8e4af03a6a6c 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1163,6 +1163,7 @@ struct intel_crtc_state {
> 	} dsi_pll;
>
> 	int max_link_bpp_x16;	/* in 1/16 bpp units */
> +	int max_pipe_bpp;	/* in 1 bpp units */
> 	int pipe_bpp;		/* in 1 bpp units */
> 	int min_hblank;
> 	struct intel_link_m_n dp_m_n;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 48845899298e4..4018b0122e8e0 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1769,7 +1769,7 @@ static int intel_dp_max_bpp(struct intel_dp *intel_dp,
> 	struct intel_connector *connector = intel_dp->attached_connector;
> 	int bpp, bpc;
>
> -	bpc = crtc_state->pipe_bpp / 3;
> +	bpc = crtc_state->max_pipe_bpp / 3;
>
> 	if (intel_dp->dfp.max_bpc)
> 		bpc = min_t(int, bpc, intel_dp->dfp.max_bpc);
> @@ -2726,7 +2726,7 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
> 		 * previously. This hack should be removed once we have the
> 		 * proper retry logic in place.
> 		 */
> -		limits->pipe.max_bpp = min(crtc_state->pipe_bpp, 24);
> +		limits->pipe.max_bpp = min(crtc_state->max_pipe_bpp, 24);
> 	} else {
> 		limits->pipe.max_bpp = intel_dp_max_bpp(intel_dp, crtc_state,
> 							respect_downstream_limits);
> @@ -2757,6 +2757,26 @@ intel_dp_compute_config_limits(struct intel_dp *intel_dp,
> 	if (dsc && !intel_dp_dsc_compute_pipe_bpp_limits(connector, limits))
> 		return false;
>
> +	/*
> +	 * crtc_state->pipe_bpp is the non-DP specific baseline (platform/EDID)
> +	 * maximum pipe BPP limited by the max-BPC connector property request.
> +	 * Since by now pipe.max_bpp is <= the above baseline BPP, the only
> +	 * remaining reason for adjusting pipe.max_bpp is the max-BPC connector
> +	 * property request. Adjust pipe.max_bpp to this request within the
> +	 * current valid pipe.min_bpp .. pipe.max_bpp range.
> +	 */
> +	limits->pipe.max_bpp = clamp(crtc_state->pipe_bpp, limits->pipe.min_bpp,
> +				     limits->pipe.max_bpp);
> +	if (dsc)
> +		limits->pipe.max_bpp = align_max_sink_dsc_input_bpp(connector,
> +								    limits->pipe.max_bpp);
> +
> +	if (limits->pipe.max_bpp != crtc_state->pipe_bpp)
> +		drm_dbg_kms(display->drm,
> +			    "[CONNECTOR:%d:%s] Adjusting requested max pipe bpp %d -> %d\n",
> +			    connector->base.base.id, connector->base.name,
> +			    crtc_state->pipe_bpp, limits->pipe.max_bpp);
> +
> 	if (is_mst || intel_dp->use_max_params) {
> 		/*
> 		 * For MST we always configure max link bw - the spec doesn't
> -- 
> 2.49.1
>
>