drm/dp: Add helpers to query the branch DSC max throughput/line-width

Add helpers to query the DP DSC sink device's per-slice throughput as
well as a DSC branch device's overall throughput and line-width
capabilities.

v2 (Ville):
- Rename pixel_clock to peak_pixel_rate, document what the value means
  in case of MST tiled displays.
- Fix name of drm_dp_dsc_branch_max_slice_throughput() to
  drm_dp_dsc_sink_max_slice_throughput().
v3:
- Fix the DSC branch device minimum valid line width value from 2560
  to 5120 pixels.
- Fix drm_dp_dsc_sink_max_slice_throughput()'s pixel_clock parameter
  name to peak_pixel_rate in header file.
- Add handling for throughput mode 0 granular delta, defined by DP
  Standard v2.1a.
v4:
- Remove the default switch case in
  drm_dp_dsc_sink_max_slice_throughput(), which is unreachable in the
  current code. (Ville)

Cc: dri-devel@lists.freedesktop.org
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reported-and-tested-by: Swati Sharma <swati2.sharma@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250930182450.563016-3-imre.deak@intel.com

1 files changed, 152 insertions, 0 deletions

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index 4cbcb685f562..1ebed7c41b0d 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -2836,6 +2836,158 @@ int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_S
 }
 EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);
 
+/*
+ * See DP Standard v2.1a 2.8.4 Minimum Slices/Display, Table 2-159 and
+ * Appendix L.1 Derivation of Slice Count Requirements.
+ */
+static int dsc_sink_min_slice_throughput(int peak_pixel_rate)
+{
+	if (peak_pixel_rate >= 4800000)
+		return 600000;
+	else if (peak_pixel_rate >= 2700000)
+		return 400000;
+	else
+		return 340000;
+}
+
+/**
+ * drm_dp_dsc_sink_max_slice_throughput() - Get a DSC sink's maximum pixel throughput per slice
+ * @dsc_dpcd: DSC sink's capabilities from DPCD
+ * @peak_pixel_rate: Cumulative peak pixel rate in kHz
+ * @is_rgb_yuv444: The mode is either RGB or YUV444
+ *
+ * Return the DSC sink device's maximum pixel throughput per slice, based on
+ * the device's @dsc_dpcd capabilities, the @peak_pixel_rate of the transferred
+ * stream(s) and whether the output format @is_rgb_yuv444 or yuv422/yuv420.
+ *
+ * Note that @peak_pixel_rate is the total pixel rate transferred to the same
+ * DSC/display sink. For instance to calculate a tile's slice count of an MST
+ * multi-tiled display sink (not considering here the required
+ * rounding/alignment of slice count)::
+ *
+ *   @peak_pixel_rate = tile_pixel_rate * tile_count
+ *   total_slice_count = @peak_pixel_rate / drm_dp_dsc_sink_max_slice_throughput(@peak_pixel_rate)
+ *   tile_slice_count = total_slice_count / tile_count
+ *
+ * Returns:
+ * The maximum pixel throughput per slice supported by the DSC sink device
+ * in kPixels/sec.
+ */
+int drm_dp_dsc_sink_max_slice_throughput(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
+					 int peak_pixel_rate, bool is_rgb_yuv444)
+{
+	int throughput;
+	int delta = 0;
+	int base;
+
+	throughput = dsc_dpcd[DP_DSC_PEAK_THROUGHPUT - DP_DSC_SUPPORT];
+
+	if (is_rgb_yuv444) {
+		throughput = (throughput & DP_DSC_THROUGHPUT_MODE_0_MASK) >>
+			     DP_DSC_THROUGHPUT_MODE_0_SHIFT;
+
+		delta = ((dsc_dpcd[DP_DSC_RC_BUF_BLK_SIZE - DP_DSC_SUPPORT]) &
+			 DP_DSC_THROUGHPUT_MODE_0_DELTA_MASK) >>
+			DP_DSC_THROUGHPUT_MODE_0_DELTA_SHIFT;	/* in units of 2 MPixels/sec */
+		delta *= 2000;
+	} else {
+		throughput = (throughput & DP_DSC_THROUGHPUT_MODE_1_MASK) >>
+			     DP_DSC_THROUGHPUT_MODE_1_SHIFT;
+	}
+
+	switch (throughput) {
+	case 0:
+		return dsc_sink_min_slice_throughput(peak_pixel_rate);
+	case 1:
+		base = 340000;
+		break;
+	case 2 ... 14:
+		base = 400000 + 50000 * (throughput - 2);
+		break;
+	case 15:
+		base = 170000;
+		break;
+	}
+
+	return base + delta;
+}
+EXPORT_SYMBOL(drm_dp_dsc_sink_max_slice_throughput);
+
+static u8 dsc_branch_dpcd_cap(const u8 dpcd[DP_DSC_BRANCH_CAP_SIZE], int reg)
+{
+	return dpcd[reg - DP_DSC_BRANCH_OVERALL_THROUGHPUT_0];
+}
+
+/**
+ * drm_dp_dsc_branch_max_overall_throughput() - Branch device's max overall DSC pixel throughput
+ * @dsc_branch_dpcd: DSC branch capabilities from DPCD
+ * @is_rgb_yuv444: The mode is either RGB or YUV444
+ *
+ * Return the branch device's maximum overall DSC pixel throughput, based on
+ * the device's DPCD DSC branch capabilities, and whether the output
+ * format @is_rgb_yuv444 or yuv422/yuv420.
+ *
+ * Returns:
+ * - 0:   The maximum overall throughput capability is not indicated by
+ *        the device separately and it must be determined from the per-slice
+ *        max throughput (see @drm_dp_dsc_branch_slice_max_throughput())
+ *        and the maximum slice count supported by the device.
+ * - > 0: The maximum overall DSC pixel throughput supported by the branch
+ *        device in kPixels/sec.
+ */
+int drm_dp_dsc_branch_max_overall_throughput(const u8 dsc_branch_dpcd[DP_DSC_BRANCH_CAP_SIZE],
+					     bool is_rgb_yuv444)
+{
+	int throughput;
+
+	if (is_rgb_yuv444)
+		throughput = dsc_branch_dpcd_cap(dsc_branch_dpcd,
+						 DP_DSC_BRANCH_OVERALL_THROUGHPUT_0);
+	else
+		throughput = dsc_branch_dpcd_cap(dsc_branch_dpcd,
+						 DP_DSC_BRANCH_OVERALL_THROUGHPUT_1);
+
+	switch (throughput) {
+	case 0:
+		return 0;
+	case 1:
+		return 680000;
+	default:
+		return 600000 + 50000 * throughput;
+	}
+}
+EXPORT_SYMBOL(drm_dp_dsc_branch_max_overall_throughput);
+
+/**
+ * drm_dp_dsc_branch_max_line_width() - Branch device's max DSC line width
+ * @dsc_branch_dpcd: DSC branch capabilities from DPCD
+ *
+ * Return the branch device's maximum overall DSC line width, based on
+ * the device's @dsc_branch_dpcd capabilities.
+ *
+ * Returns:
+ * - 0:        The maximum line width is not indicated by the device
+ *             separately and it must be determined from the maximum
+ *             slice count and slice-width supported by the device.
+ * - %-EINVAL: The device indicates an invalid maximum line width
+ *             (< 5120 pixels).
+ * - >= 5120:  The maximum line width in pixels.
+ */
+int drm_dp_dsc_branch_max_line_width(const u8 dsc_branch_dpcd[DP_DSC_BRANCH_CAP_SIZE])
+{
+	int line_width = dsc_branch_dpcd_cap(dsc_branch_dpcd, DP_DSC_BRANCH_MAX_LINE_WIDTH);
+
+	switch (line_width) {
+	case 0:
+		return 0;
+	case 1 ... 15:
+		return -EINVAL;
+	default:
+		return line_width * 320;
+	}
+}
+EXPORT_SYMBOL(drm_dp_dsc_branch_max_line_width);
+
 static int drm_dp_read_lttpr_regs(struct drm_dp_aux *aux,
 				  const u8 dpcd[DP_RECEIVER_CAP_SIZE], int address,
 				  u8 *buf, int buf_size)