drm/i915/dsc: Compute Rate Control parameters for DSC

This computation of RC params happens in the atomic commit phase
during compute_config() to validate if display stream compression
can be enabled for the requested mode.

v7 (From Manasi):
* Use DRM_DEBUG instead of DRM_ERROR (Ville)
* Use Error numberinstead of -1 (Ville)
v6 (From Manasi):
* Use 9 instead of 0x9 for consistency (Anusha)

v5 (From Manasi):
* Fix dim checkpatch warnings/checks
v4(From Gaurav):
* No change.Rebase on drm-tip

v3 (From Gaurav):
* Rebase on top of Manasi's latest series
* Return -ve value in case of failure scenarios (Manasi)

Fix review comments from Ville:
* Remove unnecessary comments
* Remove unnecessary paranthesis
* Add comments for few RC params calculations

v2 (From Manasi):
* Rebase Gaurav's patch from intel-gfx to gfx-internal
* Use struct drm_dsc_cfg instead of struct intel_dp
as a parameter

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Gaurav K Singh <gaurav.k.singh@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181128202628.20238-5-manasi.d.navare@intel.com

drivers/gpu/drm/i915/intel_vdsc.c

@@ -318,6 +318,129 @@ static int get_column_index_for_rc_params(u8 bits_per_component)
 	}
 }
 
+static int intel_compute_rc_parameters(struct drm_dsc_config *vdsc_cfg)
+{
+	unsigned long groups_per_line = 0;
+	unsigned long groups_total = 0;
+	unsigned long num_extra_mux_bits = 0;
+	unsigned long slice_bits = 0;
+	unsigned long hrd_delay = 0;
+	unsigned long final_scale = 0;
+	unsigned long rbs_min = 0;
+
+	/* Number of groups used to code each line of a slice */
+	groups_per_line = DIV_ROUND_UP(vdsc_cfg->slice_width,
+				       DSC_RC_PIXELS_PER_GROUP);
+
+	/* chunksize in Bytes */
+	vdsc_cfg->slice_chunk_size = DIV_ROUND_UP(vdsc_cfg->slice_width *
+						  vdsc_cfg->bits_per_pixel,
+						  (8 * 16));
+
+	if (vdsc_cfg->convert_rgb)
+		num_extra_mux_bits = 3 * (vdsc_cfg->mux_word_size +
+					  (4 * vdsc_cfg->bits_per_component + 4)
+					  - 2);
+	else
+		num_extra_mux_bits = 3 * vdsc_cfg->mux_word_size +
+			(4 * vdsc_cfg->bits_per_component + 4) +
+			2 * (4 * vdsc_cfg->bits_per_component) - 2;
+	/* Number of bits in one Slice */
+	slice_bits = 8 * vdsc_cfg->slice_chunk_size * vdsc_cfg->slice_height;
+
+	while ((num_extra_mux_bits > 0) &&
+	       ((slice_bits - num_extra_mux_bits) % vdsc_cfg->mux_word_size))
+		num_extra_mux_bits--;
+
+	if (groups_per_line < vdsc_cfg->initial_scale_value - 8)
+		vdsc_cfg->initial_scale_value = groups_per_line + 8;
+
+	/* scale_decrement_interval calculation according to DSC spec 1.11 */
+	if (vdsc_cfg->initial_scale_value > 8)
+		vdsc_cfg->scale_decrement_interval = groups_per_line /
+			(vdsc_cfg->initial_scale_value - 8);
+	else
+		vdsc_cfg->scale_decrement_interval = DSC_SCALE_DECREMENT_INTERVAL_MAX;
+
+	vdsc_cfg->final_offset = vdsc_cfg->rc_model_size -
+		(vdsc_cfg->initial_xmit_delay *
+		 vdsc_cfg->bits_per_pixel + 8) / 16 + num_extra_mux_bits;
+
+	if (vdsc_cfg->final_offset >= vdsc_cfg->rc_model_size) {
+		DRM_DEBUG_KMS("FinalOfs < RcModelSze for this InitialXmitDelay\n");
+		return -ERANGE;
+	}
+
+	final_scale = (vdsc_cfg->rc_model_size * 8) /
+		(vdsc_cfg->rc_model_size - vdsc_cfg->final_offset);
+	if (vdsc_cfg->slice_height > 1)
+		/*
+		 * NflBpgOffset is 16 bit value with 11 fractional bits
+		 * hence we multiply by 2^11 for preserving the
+		 * fractional part
+		 */
+		vdsc_cfg->nfl_bpg_offset = DIV_ROUND_UP((vdsc_cfg->first_line_bpg_offset << 11),
+							(vdsc_cfg->slice_height - 1));
+	else
+		vdsc_cfg->nfl_bpg_offset = 0;
+
+	/* 2^16 - 1 */
+	if (vdsc_cfg->nfl_bpg_offset > 65535) {
+		DRM_DEBUG_KMS("NflBpgOffset is too large for this slice height\n");
+		return -ERANGE;
+	}
+
+	/* Number of groups used to code the entire slice */
+	groups_total = groups_per_line * vdsc_cfg->slice_height;
+
+	/* slice_bpg_offset is 16 bit value with 11 fractional bits */
+	vdsc_cfg->slice_bpg_offset = DIV_ROUND_UP(((vdsc_cfg->rc_model_size -
+						    vdsc_cfg->initial_offset +
+						    num_extra_mux_bits) << 11),
+						  groups_total);
+
+	if (final_scale > 9) {
+		/*
+		 * ScaleIncrementInterval =
+		 * finaloffset/((NflBpgOffset + SliceBpgOffset)*8(finalscale - 1.125))
+		 * as (NflBpgOffset + SliceBpgOffset) has 11 bit fractional value,
+		 * we need divide by 2^11 from pstDscCfg values
+		 */
+		vdsc_cfg->scale_increment_interval =
+				(vdsc_cfg->final_offset * (1 << 11)) /
+				((vdsc_cfg->nfl_bpg_offset +
+				vdsc_cfg->slice_bpg_offset) *
+				(final_scale - 9));
+	} else {
+		/*
+		 * If finalScaleValue is less than or equal to 9, a value of 0 should
+		 * be used to disable the scale increment at the end of the slice
+		 */
+		vdsc_cfg->scale_increment_interval = 0;
+	}
+
+	if (vdsc_cfg->scale_increment_interval > 65535) {
+		DRM_DEBUG_KMS("ScaleIncrementInterval is large for slice height\n");
+		return -ERANGE;
+	}
+
+	/*
+	 * DSC spec mentions that bits_per_pixel specifies the target
+	 * bits/pixel (bpp) rate that is used by the encoder,
+	 * in steps of 1/16 of a bit per pixel
+	 */
+	rbs_min = vdsc_cfg->rc_model_size - vdsc_cfg->initial_offset +
+		DIV_ROUND_UP(vdsc_cfg->initial_xmit_delay *
+			     vdsc_cfg->bits_per_pixel, 16) +
+		groups_per_line * vdsc_cfg->first_line_bpg_offset;
+
+	hrd_delay = DIV_ROUND_UP((rbs_min * 16), vdsc_cfg->bits_per_pixel);
+	vdsc_cfg->rc_bits = (hrd_delay * vdsc_cfg->bits_per_pixel) / 16;
+	vdsc_cfg->initial_dec_delay = hrd_delay - vdsc_cfg->initial_xmit_delay;
+
+	return 0;
+}
+
 int intel_dp_compute_dsc_params(struct intel_dp *intel_dp,
 				struct intel_crtc_state *pipe_config)
 {
@@ -452,5 +575,5 @@ int intel_dp_compute_dsc_params(struct intel_dp *intel_dp,
 	vdsc_cfg->initial_scale_value = (vdsc_cfg->rc_model_size << 3) /
 		(vdsc_cfg->rc_model_size - vdsc_cfg->initial_offset);
 
-	return 0;
+	return intel_compute_rc_parameters(vdsc_cfg);
 }