drm/i915/dp: Limit max link bpp properly to a fractional value on SST

The maximum link bpp - determined by the link BW for instance - can be
fractional, handle this properly during computing the link bpp on SST.

This keeps the pipe joiner specific maximum link bpp as a rounded-down
integer value still, changing that to a fractional value is left for
later.

v2: Align the min/max bpp value to the bpp step.

Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250509180340.554867-8-imre.deak@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index f8de29d8a4da46be8320efdbf330e6e328577cf9..b91c1e43051a17da1912d39a1f441b887f88117d 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -27,6 +27,8 @@
 
 #include <linux/export.h>
 #include <linux/i2c.h>
+#include <linux/log2.h>
+#include <linux/math.h>
 #include <linux/notifier.h>
 #include <linux/seq_buf.h>
 #include <linux/slab.h>
@@ -939,6 +941,7 @@ static u32 ultrajoiner_ram_max_bpp(u32 mode_hdisplay)
        return ultrajoiner_ram_bits() / mode_hdisplay;
 }
 
+/* TODO: return a bpp_x16 value */
 static
 u32 get_max_compressed_bpp_with_joiner(struct intel_display *display,
                                       u32 mode_clock, u32 mode_hdisplay,
@@ -2153,24 +2156,16 @@ static int dsc_compute_compressed_bpp(struct intel_dp *intel_dp,
        const struct intel_connector *connector = to_intel_connector(conn_state->connector);
        const struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
        int output_bpp;
-       int dsc_min_bpp;
-       int dsc_max_bpp;
        int min_bpp_x16, max_bpp_x16, bpp_step_x16;
        int dsc_joiner_max_bpp;
        int num_joined_pipes = intel_crtc_num_joined_pipes(pipe_config);
        int bpp_x16;
        int ret;
 
-       dsc_min_bpp = fxp_q4_to_int_roundup(limits->link.min_bpp_x16);
-
        dsc_joiner_max_bpp = get_max_compressed_bpp_with_joiner(display, adjusted_mode->clock,
                                                                adjusted_mode->hdisplay,
                                                                num_joined_pipes);
-       dsc_max_bpp = min(dsc_joiner_max_bpp, fxp_q4_to_int(limits->link.max_bpp_x16));
-
-       /* FIXME: remove the round trip via integers */
-       min_bpp_x16 = fxp_q4_from_int(dsc_min_bpp);
-       max_bpp_x16 = fxp_q4_from_int(dsc_max_bpp);
+       max_bpp_x16 = min(fxp_q4_from_int(dsc_joiner_max_bpp), limits->link.max_bpp_x16);
 
        bpp_step_x16 = intel_dp_dsc_bpp_step_x16(connector);
 
@@ -2178,6 +2173,10 @@ static int dsc_compute_compressed_bpp(struct intel_dp *intel_dp,
        output_bpp = intel_dp_output_bpp(pipe_config->output_format, pipe_bpp);
        max_bpp_x16 = min(max_bpp_x16, fxp_q4_from_int(output_bpp) - bpp_step_x16);
 
+       drm_WARN_ON(display->drm, !is_power_of_2(bpp_step_x16));
+       min_bpp_x16 = round_up(limits->link.min_bpp_x16, bpp_step_x16);
+       max_bpp_x16 = round_down(max_bpp_x16, bpp_step_x16);
+
        for (bpp_x16 = max_bpp_x16; bpp_x16 >= min_bpp_x16; bpp_x16 -= bpp_step_x16) {
                if (!intel_dp_dsc_valid_compressed_bpp(intel_dp, bpp_x16))
                        continue;