drm/i915/dp: Increase slice_height for DP

According VDSC spec 1.2a Section 3.8 Options for Slice
implies that 108 lines is an optimal slice height, but any
size can be used as long as vertical active
integer multiple and maximum vertical slice count requirements are met.

Bspec: 49259

--v3
-remove previous fallback code and return slice_height as 2 [Jani]

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Swati Sharma <swati2.sharma@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230214052017.3312044-1-suraj.kandpal@intel.com

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

@@ -1415,6 +1415,28 @@ static int intel_dp_sink_dsc_version_minor(struct intel_dp *intel_dp)
 		DP_DSC_MINOR_SHIFT;
 }
 
+static int intel_dp_get_slice_height(int vactive)
+{
+	int slice_height;
+
+	/*
+	 * VDSC 1.2a spec in Section 3.8 Options for Slices implies that 108
+	 * lines is an optimal slice height, but any size can be used as long as
+	 * vertical active integer multiple and maximum vertical slice count
+	 * requirements are met.
+	 */
+	for (slice_height = 108; slice_height <= vactive; slice_height += 2)
+		if (vactive % slice_height == 0)
+			return slice_height;
+
+	/*
+	 * Highly unlikely we reach here as most of the resolutions will end up
+	 * finding appropriate slice_height in above loop but returning
+	 * slice_height as 2 here as it should work with all resolutions.
+	 */
+	return 2;
+}
+
 static int intel_dp_dsc_compute_params(struct intel_encoder *encoder,
 				       struct intel_crtc_state *crtc_state)
 {
@@ -1433,17 +1455,7 @@ static int intel_dp_dsc_compute_params(struct intel_encoder *encoder,
 	vdsc_cfg->rc_model_size = DSC_RC_MODEL_SIZE_CONST;
 	vdsc_cfg->pic_height = crtc_state->hw.adjusted_mode.crtc_vdisplay;
 
-	/*
-	 * Slice Height of 8 works for all currently available panels. So start
-	 * with that if pic_height is an integral multiple of 8. Eventually add
-	 * logic to try multiple slice heights.
-	 */
-	if (vdsc_cfg->pic_height % 8 == 0)
-		vdsc_cfg->slice_height = 8;
-	else if (vdsc_cfg->pic_height % 4 == 0)
-		vdsc_cfg->slice_height = 4;
-	else
-		vdsc_cfg->slice_height = 2;
+	vdsc_cfg->slice_height = intel_dp_get_slice_height(vdsc_cfg->pic_height);
 
 	ret = intel_dsc_compute_params(crtc_state);
 	if (ret)