On Wed, Jan 28, 2026 at 07:36:28PM +0530, Ankit Nautiyal wrote:
> Refactor the logic to get the number of joined pipes. Start with a single
> pipe and incrementally try additional pipes only if needed. While DSC
> overhead is not yet computed here, this restructuring prepares the code to
> support that in follow-up changes.
>
> Signed-off-by: Ankit Nautiyal <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_dp.c | 2 -
> drivers/gpu/drm/i915/display/intel_dp.h | 3 +
> drivers/gpu/drm/i915/display/intel_dp_mst.c | 86 ++++++++++++---------
> 3 files changed, 52 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index f8986f0acc79..9bbd37ebd2ea 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1371,7 +1371,6 @@ intel_dp_mode_valid_downstream(struct intel_connector
> *connector,
> return MODE_OK;
> }
>
> -static
> int intel_dp_max_hdisplay_per_pipe(struct intel_display *display)
> {
> return DISPLAY_VER(display) >= 30 ? 6144 : 5120;
> @@ -1434,7 +1433,6 @@ bool intel_dp_has_dsc(const struct intel_connector
> *connector)
> return true;
> }
>
> -static
> bool intel_dp_can_join(struct intel_display *display,
> int num_joined_pipes)
> {
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h
> b/drivers/gpu/drm/i915/display/intel_dp.h
> index 25bfbfd291b0..6d409c1998c9 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -225,5 +225,8 @@ int intel_dp_compute_config_late(struct intel_encoder
> *encoder,
> struct drm_connector_state *conn_state);
> int intel_dp_sdp_min_guardband(const struct intel_crtc_state *crtc_state,
> bool assume_all_enabled);
> +int intel_dp_max_hdisplay_per_pipe(struct intel_display *display);
> +bool intel_dp_can_join(struct intel_display *display,
> + int num_joined_pipes);
>
> #endif /* __INTEL_DP_H__ */
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index f47bf45d0bce..664004600564 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -1420,7 +1420,6 @@ mst_connector_mode_valid_ctx(struct drm_connector
> *_connector,
> struct drm_dp_mst_topology_mgr *mgr = &intel_dp->mst.mgr;
> struct drm_dp_mst_port *port = connector->mst.port;
> const int min_bpp = 18;
> - int max_dotclk = display->cdclk.max_dotclk_freq;
> int max_rate, mode_rate, max_lanes, max_link_clock;
> unsigned long bw_overhead_flags =
> DRM_DP_BW_OVERHEAD_MST | DRM_DP_BW_OVERHEAD_SSC_REF_CLK;
> @@ -1428,6 +1427,7 @@ mst_connector_mode_valid_ctx(struct drm_connector
> *_connector,
> bool dsc = false;
> int target_clock = mode->clock;
> int num_joined_pipes;
> + int num_pipes;
>
> if (drm_connector_is_unregistered(&connector->base)) {
> *status = MODE_ERROR;
> @@ -1480,50 +1480,62 @@ mst_connector_mode_valid_ctx(struct drm_connector
> *_connector,
> return 0;
> }
>
> - num_joined_pipes = intel_dp_num_joined_pipes(intel_dp, connector,
> - mode->hdisplay,
> target_clock);
> -
> - if (intel_dp_has_dsc(connector) &&
> drm_dp_sink_supports_fec(connector->dp.fec_capability)) {
> - /*
> - * TBD pass the connector BPC,
> - * for now U8_MAX so that max BPC on that platform would be
> picked
> - */
> - int pipe_bpp = intel_dp_dsc_compute_max_bpp(connector, U8_MAX);
> -
> - if (!drm_dp_is_uhbr_rate(max_link_clock))
> - bw_overhead_flags |= DRM_DP_BW_OVERHEAD_FEC;
> -
> - dsc = intel_dp_mode_valid_with_dsc(connector,
> - max_link_clock, max_lanes,
> - target_clock, mode->hdisplay,
> - num_joined_pipes,
> - INTEL_OUTPUT_FORMAT_RGB,
> pipe_bpp,
> - bw_overhead_flags);
> - }
> + for (num_pipes = 0; num_pipes < I915_MAX_PIPES; num_pipes++) {
> + int max_dotclk = display->cdclk.max_dotclk_freq;
>
> - if (intel_dp_joiner_needs_dsc(display, num_joined_pipes) && !dsc) {
> *status = MODE_CLOCK_HIGH;
> - return 0;
> - }
>
> - if (mode_rate > max_rate && !dsc) {
> - *status = MODE_CLOCK_HIGH;
> - return 0;
> - }
> + if (num_pipes == 0) {
> + if (!connector->force_joined_pipes)
> + continue;
> + num_joined_pipes = connector->force_joined_pipes;
> + } else {
> + num_joined_pipes = num_pipes;
> + }
I'd skip here the force_joined_pipes && force_joined_pipes != num_pipes
case as mentioned earlier.
>
> - *status = intel_mode_valid_max_plane_size(display, mode,
> num_joined_pipes);
> + if (!intel_dp_can_join(display, num_joined_pipes))
> + continue;
>
> - if (*status != MODE_OK)
> - return 0;
> + if (mode->hdisplay > num_joined_pipes *
> intel_dp_max_hdisplay_per_pipe(display))
> + continue;
>
> - max_dotclk *= num_joined_pipes;
> + if (intel_dp_has_dsc(connector) &&
> + drm_dp_sink_supports_fec(connector->dp.fec_capability)) {
> + /*
> + * TBD pass the connector BPC,
> + * for now U8_MAX so that max BPC on that platform
> would be picked
> + */
> + int pipe_bpp = intel_dp_dsc_compute_max_bpp(connector,
> U8_MAX);
>
> - if (mode->clock > max_dotclk) {
> - *status = MODE_CLOCK_HIGH;
> - return 0;
> - }
> + if (!drm_dp_is_uhbr_rate(max_link_clock))
> + bw_overhead_flags |= DRM_DP_BW_OVERHEAD_FEC;
> +
> + dsc = intel_dp_mode_valid_with_dsc(connector,
> + max_link_clock,
> max_lanes,
> + target_clock,
> mode->hdisplay,
> + num_joined_pipes,
> +
> INTEL_OUTPUT_FORMAT_RGB, pipe_bpp,
> + bw_overhead_flags);
> + }
>
> - *status = MODE_OK;
> + if (intel_dp_joiner_needs_dsc(display, num_joined_pipes) &&
> !dsc)
> + continue;
> +
> + if (mode_rate > max_rate && !dsc)
> + continue;
> +
> + *status = intel_mode_valid_max_plane_size(display, mode,
> num_joined_pipes);
> +
> + if (*status != MODE_OK)
> + continue;
> +
> + max_dotclk *= num_joined_pipes;
> +
> + if (mode->clock <= max_dotclk) {
> + *status = MODE_OK;
*status stays MODE_OK if mode->clock > max_dotclk.
The "histogram" diff algorithm produces for this particular patch a more
readable output.
> + break;
> + }
> + }
>
> return 0;
> }
> --
> 2.45.2
>
