drm/dsc: add helper for calculating rc buffer size from DPCD

Add a helper for calculating the rc buffer size from the DCPD offsets
DP_DSC_RC_BUF_BLK_SIZE and DP_DSC_RC_BUF_SIZE.

Cc: Alex Deucher <alexdeucher@gmail.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/6c6aee22740fe7a8cf2b8e768bfda378850cf59a.1607429866.git.jani.nikula@intel.com

drivers/gpu/drm/drm_dsc.c

@@ -49,6 +49,33 @@ void drm_dsc_dp_pps_header_init(struct dp_sdp_header *pps_header)
 }
 EXPORT_SYMBOL(drm_dsc_dp_pps_header_init);
 
+/**
+ * drm_dsc_dp_rc_buffer_size - get rc buffer size in bytes
+ * @rc_buffer_block_size: block size code, according to DPCD offset 62h
+ * @rc_buffer_size: number of blocks - 1, according to DPCD offset 63h
+ *
+ * return:
+ * buffer size in bytes, or 0 on invalid input
+ */
+int drm_dsc_dp_rc_buffer_size(u8 rc_buffer_block_size, u8 rc_buffer_size)
+{
+	int size = 1024 * (rc_buffer_size + 1);
+
+	switch (rc_buffer_block_size) {
+	case DP_DSC_RC_BUF_BLK_SIZE_1:
+		return 1 * size;
+	case DP_DSC_RC_BUF_BLK_SIZE_4:
+		return 4 * size;
+	case DP_DSC_RC_BUF_BLK_SIZE_16:
+		return 16 * size;
+	case DP_DSC_RC_BUF_BLK_SIZE_64:
+		return 64 * size;
+	default:
+		return 0;
+	}
+}
+EXPORT_SYMBOL(drm_dsc_dp_rc_buffer_size);
+
 /**
  * drm_dsc_pps_payload_pack() - Populates the DSC PPS
  *

include/drm/drm_dsc.h

@@ -602,6 +602,7 @@ struct drm_dsc_pps_infoframe {
 } __packed;
 
 void drm_dsc_dp_pps_header_init(struct dp_sdp_header *pps_header);
+int drm_dsc_dp_rc_buffer_size(u8 rc_buffer_block_size, u8 rc_buffer_size);
 void drm_dsc_pps_payload_pack(struct drm_dsc_picture_parameter_set *pps_sdp,
 				const struct drm_dsc_config *dsc_cfg);
 int drm_dsc_compute_rc_parameters(struct drm_dsc_config *vdsc_cfg);