drm/i915/dsc/mtl: Add support for fractional bpp

Consider the fractional bpp while reading the qp values.

v2: Use helpers for fractional, integral bits of bits_per_pixel. (Suraj)
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20231110101020.4067342-6-ankit.k.nautiyal@intel.com

drivers/gpu/drm/i915/display/intel_qp_tables.c

@@ -34,9 +34,6 @@
  * These qp tables are as per the C model
  * and it has the rows pointing to bpps which increment
  * in steps of 0.5
- * We do not support fractional bpps as of today,
- * hence we would skip the fractional bpps during
- * our references for qp calclulations.
  */
 static const u8 rc_range_minqp444_8bpc[DSC_NUM_BUF_RANGES][RC_RANGE_QP444_8BPC_MAX_NUM_BPP] = {
 	{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

drivers/gpu/drm/i915/display/intel_vdsc.c

@@ -77,8 +77,8 @@ intel_vdsc_set_min_max_qp(struct drm_dsc_config *vdsc_cfg, int buf,
 static void
 calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
 {
+	int bpp = to_bpp_int(vdsc_cfg->bits_per_pixel);
 	int bpc = vdsc_cfg->bits_per_component;
-	int bpp = vdsc_cfg->bits_per_pixel >> 4;
 	int qp_bpc_modifier = (bpc - 8) * 2;
 	int uncompressed_bpg_rate;
 	int first_line_bpg_offset;
@@ -148,7 +148,13 @@ calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
 		static const s8 ofs_und8[] = {
 			10, 8, 6, 4, 2, 0, -2, -4, -6, -8, -10, -10, -12, -12, -12
 		};
-
+		/*
+		 * For 420 format since bits_per_pixel (bpp) is set to target bpp * 2,
+		 * QP table values for target bpp 4.0 to 4.4375 (rounded to 4.0) are
+		 * actually for bpp 8 to 8.875 (rounded to 4.0 * 2 i.e 8).
+		 * Similarly values for target bpp 4.5 to 4.8375 (rounded to 4.5)
+		 * are for bpp 9 to 9.875 (rounded to 4.5 * 2 i.e 9), and so on.
+		 */
 		bpp_i  = bpp - 8;
 		for (buf_i = 0; buf_i < DSC_NUM_BUF_RANGES; buf_i++) {
 			u8 range_bpg_offset;
@@ -178,6 +184,9 @@ calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
 				range_bpg_offset & DSC_RANGE_BPG_OFFSET_MASK;
 		}
 	} else {
+		/* fractional bpp part * 10000 (for precision up to 4 decimal places) */
+		int fractional_bits = to_bpp_frac(vdsc_cfg->bits_per_pixel);
+
 		static const s8 ofs_und6[] = {
 			0, -2, -2, -4, -6, -6, -8, -8, -8, -10, -10, -12, -12, -12, -12
 		};
@@ -191,7 +200,14 @@ calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
 			10, 8, 6, 4, 2, 0, -2, -4, -6, -8, -10, -10, -12, -12, -12
 		};
 
-		bpp_i  = (2 * (bpp - 6));
+		/*
+		 * QP table rows have values in increment of 0.5.
+		 * So 6.0 bpp to 6.4375 will have index 0, 6.5 to 6.9375 will have index 1,
+		 * and so on.
+		 * 0.5 fractional part with 4 decimal precision becomes 5000
+		 */
+		bpp_i  = ((bpp - 6) + (fractional_bits < 5000 ? 0 : 1));
+
 		for (buf_i = 0; buf_i < DSC_NUM_BUF_RANGES; buf_i++) {
 			u8 range_bpg_offset;
 
@@ -279,8 +295,7 @@ int intel_dsc_compute_params(struct intel_crtc_state *pipe_config)
 	/* Gen 11 does not support VBR */
 	vdsc_cfg->vbr_enable = false;
 
-	/* Gen 11 only supports integral values of bpp */
-	vdsc_cfg->bits_per_pixel = compressed_bpp << 4;
+	vdsc_cfg->bits_per_pixel = pipe_config->dsc.compressed_bpp_x16;
 
 	/*
 	 * According to DSC 1.2 specs in Section 4.1 if native_420 is set