drm/display/dp: Export fn to calculate link symbol cycles

Unify the function to calculate the link symbol cycles for both dsc and
non-dsc case and export the function so that it can be used in the
respective platform display drivers for other calculations.

v2: unify the fn for both dsc and non-dsc case (Imre)
v3: rename drm_dp_link_symbol_cycles to drm_dp_link_data_symbol_cycles
    retain slice_eoc_cycles as is (Imre)
v4: Expose only drm_dp_link_symbol_cycles() (Imre)
v6: Add slice pixels which was removed unknowingly (Vinod)

Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.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/20250424-hblank-v7-1-8b002f1506cc@intel.com

2 files changed, 36 insertions, 18 deletions

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index f5c596234729..8f774221eeb3 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -4324,8 +4324,9 @@ EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
 #endif
 
 /* See DP Standard v2.1 2.6.4.4.1.1, 2.8.4.4, 2.8.7 */
-static int drm_dp_link_symbol_cycles(int lane_count, int pixels, int bpp_x16,
-				     int symbol_size, bool is_mst)
+static int drm_dp_link_data_symbol_cycles(int lane_count, int pixels,
+					  int bpp_x16, int symbol_size,
+					  bool is_mst)
 {
 	int cycles = DIV_ROUND_UP(pixels * bpp_x16, 16 * symbol_size * lane_count);
 	int align = is_mst ? 4 / lane_count : 1;
@@ -4333,22 +4334,42 @@ static int drm_dp_link_symbol_cycles(int lane_count, int pixels, int bpp_x16,
 	return ALIGN(cycles, align);
 }
 
-static int drm_dp_link_dsc_symbol_cycles(int lane_count, int pixels, int slice_count,
-					 int bpp_x16, int symbol_size, bool is_mst)
+/**
+ * drm_dp_link_symbol_cycles - calculate the link symbol count with/without dsc
+ * @lane_count: DP link lane count
+ * @pixels: number of pixels in a scanline
+ * @dsc_slice_count: number of slices for DSC or '0' for non-DSC
+ * @bpp_x16: bits per pixel in .4 binary fixed format
+ * @symbol_size: DP symbol size
+ * @is_mst: %true for MST and %false for SST
+ *
+ * Calculate the link symbol cycles for both DSC (@dsc_slice_count !=0) and
+ * non-DSC case (@dsc_slice_count == 0) and return the count.
+ */
+int drm_dp_link_symbol_cycles(int lane_count, int pixels, int dsc_slice_count,
+			      int bpp_x16, int symbol_size, bool is_mst)
 {
+	int slice_count = dsc_slice_count ? : 1;
 	int slice_pixels = DIV_ROUND_UP(pixels, slice_count);
-	int slice_data_cycles = drm_dp_link_symbol_cycles(lane_count, slice_pixels,
-							  bpp_x16, symbol_size, is_mst);
-	int slice_eoc_cycles = is_mst ? 4 / lane_count : 1;
+	int slice_data_cycles = drm_dp_link_data_symbol_cycles(lane_count,
+							       slice_pixels,
+							       bpp_x16,
+							       symbol_size,
+							       is_mst);
+	int slice_eoc_cycles = 0;
+
+	if (dsc_slice_count)
+		slice_eoc_cycles = is_mst ? 4 / lane_count : 1;
 
 	return slice_count * (slice_data_cycles + slice_eoc_cycles);
 }
+EXPORT_SYMBOL(drm_dp_link_symbol_cycles);
 
 /**
  * drm_dp_bw_overhead - Calculate the BW overhead of a DP link stream
  * @lane_count: DP link lane count
  * @hactive: pixel count of the active period in one scanline of the stream
- * @dsc_slice_count: DSC slice count if @flags/DRM_DP_LINK_BW_OVERHEAD_DSC is set
+ * @dsc_slice_count: number of slices for DSC or '0' for non-DSC
  * @bpp_x16: bits per pixel in .4 binary fixed point
  * @flags: DRM_DP_OVERHEAD_x flags
  *
@@ -4362,7 +4383,7 @@ static int drm_dp_link_dsc_symbol_cycles(int lane_count, int pixels, int slice_c
  * as well as the stream's
  * - @hactive timing
  * - @bpp_x16 color depth
- * - compression mode (@flags / %DRM_DP_OVERHEAD_DSC).
+ * - compression mode (@dsc_slice_count != 0)
  * Note that this overhead doesn't account for the 8b/10b, 128b/132b
  * channel coding efficiency, for that see
  * @drm_dp_link_bw_channel_coding_efficiency().
@@ -4417,15 +4438,10 @@ int drm_dp_bw_overhead(int lane_count, int hactive,
 	WARN_ON((flags & DRM_DP_BW_OVERHEAD_UHBR) &&
 		(flags & DRM_DP_BW_OVERHEAD_FEC));
 
-	if (flags & DRM_DP_BW_OVERHEAD_DSC)
-		symbol_cycles = drm_dp_link_dsc_symbol_cycles(lane_count, hactive,
-							      dsc_slice_count,
-							      bpp_x16, symbol_size,
-							      is_mst);
-	else
-		symbol_cycles = drm_dp_link_symbol_cycles(lane_count, hactive,
-							  bpp_x16, symbol_size,
-							  is_mst);
+	symbol_cycles = drm_dp_link_symbol_cycles(lane_count, hactive,
+						  dsc_slice_count,
+						  bpp_x16, symbol_size,
+						  is_mst);
 
 	return DIV_ROUND_UP_ULL(mul_u32_u32(symbol_cycles * symbol_size * lane_count,
 					    overhead * 16),
diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
index 89a34dff85a4..36ca21d6a399 100644
--- a/include/drm/display/drm_dp_helper.h
+++ b/include/drm/display/drm_dp_helper.h
@@ -879,5 +879,7 @@ int drm_dp_bw_channel_coding_efficiency(bool is_uhbr);
 int drm_dp_max_dprx_data_rate(int max_link_rate, int max_lanes);
 
 ssize_t drm_dp_vsc_sdp_pack(const struct drm_dp_vsc_sdp *vsc, struct dp_sdp *sdp);
+int drm_dp_link_symbol_cycles(int lane_count, int pixels, int dsc_slice_count,
+			      int bpp_x16, int symbol_size, bool is_mst);
 
 #endif /* _DRM_DP_HELPER_H_ */