drm/amd/display: take max dsc stream bandwidth overhead into account

[why]
As hardware team suggested that we need to add a max dsc bw overhead
into existing stream bandwidth when DSC is used.
The formula as below:

max_dsc_bw_overhead =
v_addressable * slice_count * 256 bit * pixel clock / v_total / h_total

effective stream bandwidth = pixel clock * bpp

stream bandwidth = effective stream bandwidth + dsc stream overhead
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Reviewed-by: Eric Bernstein <Eric.Bernstein@amd.com>
Acked-by: Wayne Lin <waynelin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -3486,9 +3486,10 @@ uint32_t dc_bandwidth_in_kbps_from_timing(
 	uint32_t kbps;
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
-	if (timing->flags.DSC) {
-		return dc_dsc_stream_bandwidth_in_kbps(timing->pix_clk_100hz, timing->dsc_cfg.bits_per_pixel);
-	}
+	if (timing->flags.DSC)
+		return dc_dsc_stream_bandwidth_in_kbps(timing,
+				timing->dsc_cfg.bits_per_pixel,
+				timing->dsc_cfg.num_slices_h);
 #endif
 
 	switch (timing->display_color_depth) {

drivers/gpu/drm/amd/display/dc/dc_dsc.h

@@ -78,7 +78,8 @@ bool dc_dsc_compute_config(
 		const struct dc_crtc_timing *timing,
 		struct dc_dsc_config *dsc_cfg);
 
-uint32_t dc_dsc_stream_bandwidth_in_kbps(uint32_t pix_clk_100hz, uint32_t bpp_x16);
+uint32_t dc_dsc_stream_bandwidth_in_kbps(const struct dc_crtc_timing *timing,
+		uint32_t bpp_x16, uint32_t num_slices_h);
 
 void dc_dsc_get_policy_for_timing(const struct dc_crtc_timing *timing,
 		uint32_t max_target_bpp_limit_override_x16,
@@ -88,6 +89,4 @@ void dc_dsc_policy_set_max_target_bpp_limit(uint32_t limit);
 
 void dc_dsc_policy_set_enable_dsc_when_not_needed(bool enable);
 
-uint32_t dc_dsc_stream_bandwidth_in_kbps(uint32_t pix_clk_100hz, uint32_t bpp_x16);
-
 #endif

drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c

@@ -258,12 +258,58 @@ static inline uint32_t dsc_div_by_10_round_up(uint32_t value)
 	return (value + 9) / 10;
 }
 
+static struct fixed31_32 compute_dsc_max_bandwidth_overhead(
+		const struct dc_crtc_timing *timing,
+		const int num_slices_h)
+{
+	struct fixed31_32 max_dsc_overhead;
+	struct fixed31_32 refresh_rate;
+
+	/* use target bpp that can take entire target bandwidth */
+	refresh_rate = dc_fixpt_from_int(timing->pix_clk_100hz);
+	refresh_rate = dc_fixpt_div_int(refresh_rate, timing->h_total);
+	refresh_rate = dc_fixpt_div_int(refresh_rate, timing->v_total);
+	refresh_rate = dc_fixpt_mul_int(refresh_rate, 100);
+
+	max_dsc_overhead = dc_fixpt_from_int(num_slices_h);
+	max_dsc_overhead = dc_fixpt_mul_int(max_dsc_overhead, timing->v_addressable);
+	max_dsc_overhead = dc_fixpt_mul_int(max_dsc_overhead, 256);
+	max_dsc_overhead = dc_fixpt_div_int(max_dsc_overhead, 1000);
+	max_dsc_overhead = dc_fixpt_mul(max_dsc_overhead, refresh_rate);
+
+	return max_dsc_overhead;
+}
+
+static uint32_t compute_bpp_x16_from_target_bandwidth(
+		const uint32_t bandwidth_in_kbps,
+		const struct dc_crtc_timing *timing,
+		const uint32_t num_slices_h,
+		const uint32_t bpp_increment_div)
+{
+	struct fixed31_32 overhead_in_kbps;
+	struct fixed31_32 effective_bandwidth_in_kbps;
+	struct fixed31_32 bpp_x16;
+
+	overhead_in_kbps = compute_dsc_max_bandwidth_overhead(
+				timing, num_slices_h);
+	effective_bandwidth_in_kbps = dc_fixpt_from_int(bandwidth_in_kbps);
+	effective_bandwidth_in_kbps = dc_fixpt_sub(effective_bandwidth_in_kbps,
+			overhead_in_kbps);
+	bpp_x16 = dc_fixpt_mul_int(effective_bandwidth_in_kbps, 10);
+	bpp_x16 = dc_fixpt_div_int(bpp_x16, timing->pix_clk_100hz);
+	bpp_x16 = dc_fixpt_from_int(dc_fixpt_floor(dc_fixpt_mul_int(bpp_x16, bpp_increment_div)));
+	bpp_x16 = dc_fixpt_div_int(bpp_x16, bpp_increment_div);
+	bpp_x16 = dc_fixpt_mul_int(bpp_x16, 16);
+	return dc_fixpt_floor(bpp_x16);
+}
+
 /* Get DSC bandwidth range based on [min_bpp, max_bpp] target bitrate range, and timing's pixel clock
  * and uncompressed bandwidth.
  */
 static void get_dsc_bandwidth_range(
 		const uint32_t min_bpp_x16,
 		const uint32_t max_bpp_x16,
+		const uint32_t num_slices_h,
 		const struct dsc_enc_caps *dsc_caps,
 		const struct dc_crtc_timing *timing,
 		struct dc_dsc_bw_range *range)
@@ -272,16 +318,20 @@ static void get_dsc_bandwidth_range(
 	range->stream_kbps = dc_bandwidth_in_kbps_from_timing(timing);
 
 	/* max dsc target bpp */
-	range->max_kbps = dc_dsc_stream_bandwidth_in_kbps(timing->pix_clk_100hz, max_bpp_x16);
+	range->max_kbps = dc_dsc_stream_bandwidth_in_kbps(timing,
+			max_bpp_x16, num_slices_h);
 	range->max_target_bpp_x16 = max_bpp_x16;
 	if (range->max_kbps > range->stream_kbps) {
 		/* max dsc target bpp is capped to native bandwidth */
 		range->max_kbps = range->stream_kbps;
-		range->max_target_bpp_x16 = calc_dsc_bpp_x16(range->stream_kbps, timing->pix_clk_100hz, dsc_caps->bpp_increment_div);
+		range->max_target_bpp_x16 = compute_bpp_x16_from_target_bandwidth(
+				range->max_kbps, timing, num_slices_h,
+				dsc_caps->bpp_increment_div);
 	}
 
 	/* min dsc target bpp */
-	range->min_kbps = dc_dsc_stream_bandwidth_in_kbps(timing->pix_clk_100hz, min_bpp_x16);
+	range->min_kbps = dc_dsc_stream_bandwidth_in_kbps(timing,
+			min_bpp_x16, num_slices_h);
 	range->min_target_bpp_x16 = min_bpp_x16;
 	if (range->min_kbps > range->max_kbps) {
 		/* min dsc target bpp is capped to max dsc bandwidth*/
@@ -290,7 +340,6 @@ static void get_dsc_bandwidth_range(
 	}
 }
 
-
 /* Decides if DSC should be used and calculates target bpp if it should, applying DSC policy.
  *
  * Returns:
@@ -303,6 +352,7 @@ static bool decide_dsc_target_bpp_x16(
 		const struct dsc_enc_caps *dsc_common_caps,
 		const int target_bandwidth_kbps,
 		const struct dc_crtc_timing *timing,
+		const int num_slices_h,
 		int *target_bpp_x16)
 {
 	bool should_use_dsc = false;
@@ -311,7 +361,7 @@ static bool decide_dsc_target_bpp_x16(
 	memset(&range, 0, sizeof(range));
 
 	get_dsc_bandwidth_range(policy->min_target_bpp * 16, policy->max_target_bpp * 16,
-			dsc_common_caps, timing, &range);
+			num_slices_h, dsc_common_caps, timing, &range);
 	if (!policy->enable_dsc_when_not_needed && target_bandwidth_kbps >= range.stream_kbps) {
 		/* enough bandwidth without dsc */
 		*target_bpp_x16 = 0;
@@ -327,7 +377,11 @@ static bool decide_dsc_target_bpp_x16(
 		should_use_dsc = true;
 	} else if (target_bandwidth_kbps >= range.min_kbps) {
 		/* use target bpp that can take entire target bandwidth */
-		*target_bpp_x16 = calc_dsc_bpp_x16(target_bandwidth_kbps, timing->pix_clk_100hz, dsc_common_caps->bpp_increment_div);
+		*target_bpp_x16 = compute_bpp_x16_from_target_bandwidth(
+				range.max_kbps, timing, num_slices_h,
+				dsc_common_caps->bpp_increment_div);
+		if (*target_bpp_x16 < range.min_kbps)
+			*target_bpp_x16 = range.min_kbps;
 		should_use_dsc = true;
 	} else {
 		/* not enough bandwidth to fulfill minimum requirement */
@@ -531,18 +585,6 @@ static bool setup_dsc_config(
 	if (!is_dsc_possible)
 		goto done;
 
-	if (target_bandwidth_kbps > 0) {
-		is_dsc_possible = decide_dsc_target_bpp_x16(
-				&policy,
-				&dsc_common_caps,
-				target_bandwidth_kbps,
-				timing,
-				&target_bpp);
-		dsc_cfg->bits_per_pixel = target_bpp;
-	}
-	if (!is_dsc_possible)
-		goto done;
-
 	sink_per_slice_throughput_mps = 0;
 
 	// Validate available DSC settings against the mode timing
@@ -690,6 +732,19 @@ static bool setup_dsc_config(
 
 	dsc_cfg->num_slices_v = pic_height/slice_height;
 
+	if (target_bandwidth_kbps > 0) {
+		is_dsc_possible = decide_dsc_target_bpp_x16(
+				&policy,
+				&dsc_common_caps,
+				target_bandwidth_kbps,
+				timing,
+				num_slices_h,
+				&target_bpp);
+		dsc_cfg->bits_per_pixel = target_bpp;
+	}
+	if (!is_dsc_possible)
+		goto done;
+
 	// Final decission: can we do DSC or not?
 	if (is_dsc_possible) {
 		// Fill out the rest of DSC settings
@@ -838,7 +893,8 @@ bool dc_dsc_compute_bandwidth_range(
 				dsc_min_slice_height_override, max_bpp_x16, &config);
 
 	if (is_dsc_possible)
-		get_dsc_bandwidth_range(min_bpp_x16, max_bpp_x16, &dsc_common_caps, timing, range);
+		get_dsc_bandwidth_range(min_bpp_x16, max_bpp_x16,
+				config.num_slices_h, &dsc_common_caps, timing, range);
 
 	return is_dsc_possible;
 }
@@ -864,13 +920,20 @@ bool dc_dsc_compute_config(
 	return is_dsc_possible;
 }
 
-uint32_t dc_dsc_stream_bandwidth_in_kbps(uint32_t pix_clk_100hz, uint32_t bpp_x16)
+uint32_t dc_dsc_stream_bandwidth_in_kbps(const struct dc_crtc_timing *timing,
+		uint32_t bpp_x16, uint32_t num_slices_h)
 {
-	struct fixed31_32 link_bw_kbps;
-	link_bw_kbps = dc_fixpt_from_int(pix_clk_100hz);
-	link_bw_kbps = dc_fixpt_div_int(link_bw_kbps, 160);
-	link_bw_kbps = dc_fixpt_mul_int(link_bw_kbps, bpp_x16);
-	return dc_fixpt_ceil(link_bw_kbps);
+	struct fixed31_32 overhead_in_kbps;
+	struct fixed31_32 bpp;
+	struct fixed31_32 actual_bandwidth_in_kbps;
+
+	overhead_in_kbps = compute_dsc_max_bandwidth_overhead(
+			timing, num_slices_h);
+	bpp = dc_fixpt_from_fraction(bpp_x16, 16);
+	actual_bandwidth_in_kbps = dc_fixpt_from_fraction(timing->pix_clk_100hz, 10);
+	actual_bandwidth_in_kbps = dc_fixpt_mul(actual_bandwidth_in_kbps, bpp);
+	actual_bandwidth_in_kbps = dc_fixpt_add(actual_bandwidth_in_kbps, overhead_in_kbps);
+	return dc_fixpt_ceil(actual_bandwidth_in_kbps);
 }
 
 void dc_dsc_get_policy_for_timing(const struct dc_crtc_timing *timing, uint32_t max_target_bpp_limit_override_x16, struct dc_dsc_policy *policy)

drivers/gpu/drm/amd/display/dc/dsc/rc_calc.c

@@ -284,26 +284,6 @@ static u32 _do_bytes_per_pixel_calc(int slice_width, u16 drm_bpp,
 	return bytes_per_pixel;
 }
 
-static u32 _do_calc_dsc_bpp_x16(u32 stream_bandwidth_kbps, u32 pix_clk_100hz,
-				u32 bpp_increment_div)
-{
-	u32 dsc_target_bpp_x16;
-	float f_dsc_target_bpp;
-	float f_stream_bandwidth_100bps;
-	// bpp_increment_div is actually precision
-	u32 precision = bpp_increment_div;
-
-	f_stream_bandwidth_100bps = stream_bandwidth_kbps * 10.0f;
-	f_dsc_target_bpp = f_stream_bandwidth_100bps / pix_clk_100hz;
-
-	// Round down to the nearest precision stop to bring it into DSC spec
-	// range
-	dsc_target_bpp_x16 = (u32)(f_dsc_target_bpp * precision);
-	dsc_target_bpp_x16 = (dsc_target_bpp_x16 * 16) / precision;
-
-	return dsc_target_bpp_x16;
-}
-
 /**
  * calc_rc_params - reads the user's cmdline mode
  * @rc: DC internal DSC parameters
@@ -367,26 +347,3 @@ u32 calc_dsc_bytes_per_pixel(const struct drm_dsc_config *pps)
 	DC_FP_END();
 	return ret;
 }
-
-/**
- * calc_dsc_bpp_x16 - retrieve the dsc bits per pixel
- * @stream_bandwidth_kbps:
- * @pix_clk_100hz:
- * @bpp_increment_div:
- *
- * Calculate the total of bits per pixel for DSC configuration.
- *
- * @note This calculation requires float point operation, most of it executes
- * under kernel_fpu_{begin,end}.
- */
-u32 calc_dsc_bpp_x16(u32 stream_bandwidth_kbps, u32 pix_clk_100hz,
-		     u32 bpp_increment_div)
-{
-	u32 dsc_bpp;
-
-	DC_FP_START();
-	dsc_bpp =  _do_calc_dsc_bpp_x16(stream_bandwidth_kbps, pix_clk_100hz,
-					bpp_increment_div);
-	DC_FP_END();
-	return dsc_bpp;
-}

drivers/gpu/drm/amd/display/dc/dsc/rc_calc.h

@@ -79,8 +79,6 @@ typedef struct qp_entry qp_table[];
 
 void calc_rc_params(struct rc_params *rc, const struct drm_dsc_config *pps);
 u32 calc_dsc_bytes_per_pixel(const struct drm_dsc_config *pps);
-u32 calc_dsc_bpp_x16(u32 stream_bandwidth_kbps, u32 pix_clk_100hz,
-		     u32 bpp_increment_div);
 
 #endif