drm/amd/display: move bpp range decision in decide dsc bw range function

[why]
Before get dsc bw range is used to compute DSC bw range
based on the given fixed bpp min/max input.
The new change will merge any specs, signal, timing specific
bpp range decision into this function. So the function needs to make
a decision with all aspects considered.

Acked-by: Mikita Lipski <[e-mail]>
Signed-off-by: Wenjing Liu <[e-mail]>
Reviewed-by: George Shen <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 	int min_slice_height; // Must not be less than 8
 	uint32_t max_target_bpp;
 	uint32_t min_target_bpp;
-	uint32_t preferred_bpp_x16;
 	bool enable_dsc_when_not_needed;
 };
 
···
 		const int num_slices_h,
 		const bool is_dp);
 
+/* TODO - Hardware/specs limitation should be owned by dc dsc and returned to DM,
+ * and DM can choose to OVERRIDE the limitation on CASE BY CASE basis.
+ * Hardware/specs limitation should not be writable by DM.
+ * It should be decoupled from DM specific policy and named differently.
+ */
 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/dc_dsc.c

···
 
 static bool dsc_policy_disable_dsc_stream_overhead;
 
+#ifndef MAX
+#define MAX(X, Y) ((X) > (Y) ? (X) : (Y))
+#endif
+#ifndef MIN
+#define MIN(X, Y) ((X) < (Y) ? (X) : (Y))
+#endif
+
 /* Forward Declerations */
-static void get_dsc_bandwidth_range(
+static bool decide_dsc_bandwidth_range(
 		const uint32_t min_bpp_x16,
 		const uint32_t max_bpp_x16,
 		const uint32_t num_slices_h,
···
 				dsc_min_slice_height_override, max_bpp_x16, &config);
 
 	if (is_dsc_possible)
-		get_dsc_bandwidth_range(min_bpp_x16, max_bpp_x16,
+		is_dsc_possible = decide_dsc_bandwidth_range(min_bpp_x16, max_bpp_x16,
 				config.num_slices_h, &dsc_common_caps, timing, range);
 
 	return is_dsc_possible;
···
 	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.
+/* Decide DSC bandwidth range based on signal, timing, specs specific and input min and max
+ * requirements.
+ * The range output includes decided min/max target bpp, the respective bandwidth requirements
+ * and native timing bandwidth requirement when DSC is not used.
  */
-static void get_dsc_bandwidth_range(
+static bool decide_dsc_bandwidth_range(
 		const uint32_t min_bpp_x16,
 		const uint32_t max_bpp_x16,
 		const uint32_t num_slices_h,
···
 		const struct dc_crtc_timing *timing,
 		struct dc_dsc_bw_range *range)
 {
-	/* native stream bandwidth */
-	range->stream_kbps = dc_bandwidth_in_kbps_from_timing(timing);
+	uint32_t preferred_bpp_x16 = timing->dsc_fixed_bits_per_pixel_x16;
 
-	/* max dsc target bpp */
-	range->max_kbps = dc_dsc_stream_bandwidth_in_kbps(timing,
-			max_bpp_x16, num_slices_h, dsc_caps->is_dp);
-	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 = compute_bpp_x16_from_target_bandwidth(
-				range->max_kbps, timing, num_slices_h,
-				dsc_caps->bpp_increment_div,
-				dsc_caps->is_dp);
+	memset(range, 0, sizeof(*range));
+
+	/* apply signal, timing, specs and explicitly specified DSC range requirements */
+	if (preferred_bpp_x16) {
+		if (preferred_bpp_x16 <= max_bpp_x16 &&
+				preferred_bpp_x16 >= min_bpp_x16) {
+			range->max_target_bpp_x16 = preferred_bpp_x16;
+			range->min_target_bpp_x16 = preferred_bpp_x16;
+		}
+	}
+	else {
+		range->max_target_bpp_x16 = max_bpp_x16;
+		range->min_target_bpp_x16 = min_bpp_x16;
 	}
 
-	/* min dsc target bpp */
-	range->min_kbps = dc_dsc_stream_bandwidth_in_kbps(timing,
-			min_bpp_x16, num_slices_h, dsc_caps->is_dp);
-	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*/
-		range->min_kbps = range->max_kbps;
-		range->min_target_bpp_x16 = range->max_target_bpp_x16;
+	/* populate output structure */
+	if (range->max_target_bpp_x16 >= range->min_target_bpp_x16 && range->min_target_bpp_x16 > 0) {
+		/* native stream bandwidth */
+		range->stream_kbps = dc_bandwidth_in_kbps_from_timing(timing);
+
+		/* max dsc target bpp */
+		range->max_kbps = dc_dsc_stream_bandwidth_in_kbps(timing,
+				range->max_target_bpp_x16, num_slices_h, dsc_caps->is_dp);
+
+		/* min dsc target bpp */
+		range->min_kbps = dc_dsc_stream_bandwidth_in_kbps(timing,
+				range->min_target_bpp_x16, num_slices_h, dsc_caps->is_dp);
 	}
+
+	return range->max_kbps >= range->min_kbps && range->min_kbps > 0;
 }
 
 /* Decides if DSC should be used and calculates target bpp if it should, applying DSC policy.
  *
  * Returns:
- *     - 'true' if DSC was required by policy and was successfully applied
- *     - 'false' if DSC was not necessary (e.g. if uncompressed stream fits 'target_bandwidth_kbps'),
- *        or if it couldn't be applied based on DSC policy.
+ *     - 'true' if target bpp is decided
+ *     - 'false' if target bpp cannot be decided (e.g. cannot fit even with min DSC bpp),
  */
 static bool decide_dsc_target_bpp_x16(
 		const struct dc_dsc_policy *policy,
···
 		const int num_slices_h,
 		int *target_bpp_x16)
 {
-	bool should_use_dsc = false;
 	struct dc_dsc_bw_range range;
 
-	memset(&range, 0, sizeof(range));
+	*target_bpp_x16 = 0;
 
-	get_dsc_bandwidth_range(policy->min_target_bpp * 16, policy->max_target_bpp * 16,
-			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;
-		should_use_dsc = false;
-	} else if (policy->preferred_bpp_x16 > 0 &&
-			policy->preferred_bpp_x16 <= range.max_target_bpp_x16 &&
-			policy->preferred_bpp_x16 >= range.min_target_bpp_x16) {
-		*target_bpp_x16 = policy->preferred_bpp_x16;
-		should_use_dsc = true;
-	} else if (target_bandwidth_kbps >= range.max_kbps) {
-		/* use max target bpp allowed */
-		*target_bpp_x16 = range.max_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 = compute_bpp_x16_from_target_bandwidth(
-				target_bandwidth_kbps, timing, num_slices_h,
-				dsc_common_caps->bpp_increment_div,
-				dsc_common_caps->is_dp);
-		should_use_dsc = true;
-	} else {
-		/* not enough bandwidth to fulfill minimum requirement */
-		*target_bpp_x16 = 0;
-		should_use_dsc = false;
+	if (decide_dsc_bandwidth_range(policy->min_target_bpp * 16, policy->max_target_bpp * 16,
+			num_slices_h, dsc_common_caps, timing, &range)) {
+		if (target_bandwidth_kbps >= range.stream_kbps) {
+			if (policy->enable_dsc_when_not_needed)
+				/* enable max bpp even dsc is not needed */
+				*target_bpp_x16 = range.max_target_bpp_x16;
+		} else if (target_bandwidth_kbps >= range.max_kbps) {
+			/* use max target bpp allowed */
+			*target_bpp_x16 = range.max_target_bpp_x16;
+		} else if (target_bandwidth_kbps >= range.min_kbps) {
+			/* use target bpp that can take entire target bandwidth */
+			*target_bpp_x16 = compute_bpp_x16_from_target_bandwidth(
+					target_bandwidth_kbps, timing, num_slices_h,
+					dsc_common_caps->bpp_increment_div,
+					dsc_common_caps->is_dp);
+		}
 	}
 
-	return should_use_dsc;
+	return *target_bpp_x16 != 0;
 }
 
 #define MIN_AVAILABLE_SLICES_SIZE  4
···
 	default:
 		return;
 	}
-
-	policy->preferred_bpp_x16 = timing->dsc_fixed_bits_per_pixel_x16;
 
 	/* internal upper limit, default 16 bpp */
 	if (policy->max_target_bpp > dsc_policy_max_target_bpp_limit)