drm/dsc: Add kernel documentation for DRM DP DSC helpers

Manasi Navare · Manasi Navare · commit 05bad2357afc · 2019-02-08T13:38:51.000-08:00
This patch adds appropriate kernel documentation for DRM DP helpers used for enabling Display Stream compression functionality in drm_dp_helper.h and drm_dp_helper.c as well as for the DSC spec related structure definitions and helpers in drm_dsc.c and drm_dsc.h Also add links between the functions and structures in the documentation. v3: * Fix the checkpatch warnings (Sean Paul) v2: * Add inline comments for longer structs (Daniel Vetter) * Split the summary and description (Daniel Vetter) Suggested-by: Daniel Vetter <daniel.vetter@intel.com> Suggested-by: Sean Paul <sean@poorly.run> Cc: Daniel Vetter <daniel.vetter@intel.com> Cc: Sean Paul <sean@poorly.run> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com> Acked-by: Sean Paul <sean@poorly.run> Reviewed-by: Daniel Vetter <daniel.vetter@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20190206213148.21390-1-manasi.d.navare@intel.com
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
@@ -1360,7 +1360,20 @@ int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc,
 EXPORT_SYMBOL(drm_dp_read_desc);
 
 /**
- * DRM DP Helpers for DSC
+ * drm_dp_dsc_sink_max_slice_count() - Get the max slice count
+ * supported by the DSC sink.
+ * @dsc_dpcd: DSC capabilities from DPCD
+ * @is_edp: true if its eDP, false for DP
+ *
+ * Read the slice capabilities DPCD register from DSC sink to get
+ * the maximum slice count supported. This is used to populate
+ * the DSC parameters in the &struct drm_dsc_config by the driver.
+ * Driver creates an infoframe using these parameters to populate
+ * &struct drm_dsc_pps_infoframe. These are sent to the sink using DSC
+ * infoframe using the helper function drm_dsc_pps_infoframe_pack()
+ *
+ * Returns:
+ * Maximum slice count supported by DSC sink or 0 its invalid
  */
 u8 drm_dp_dsc_sink_max_slice_count(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
 				   bool is_edp)
@@ -1405,6 +1418,21 @@ u8 drm_dp_dsc_sink_max_slice_count(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
 }
 EXPORT_SYMBOL(drm_dp_dsc_sink_max_slice_count);
 
+/**
+ * drm_dp_dsc_sink_line_buf_depth() - Get the line buffer depth in bits
+ * @dsc_dpcd: DSC capabilities from DPCD
+ *
+ * Read the DSC DPCD register to parse the line buffer depth in bits which is
+ * number of bits of precision within the decoder line buffer supported by
+ * the DSC sink. This is used to populate the DSC parameters in the
+ * &struct drm_dsc_config by the driver.
+ * Driver creates an infoframe using these parameters to populate
+ * &struct drm_dsc_pps_infoframe. These are sent to the sink using DSC
+ * infoframe using the helper function drm_dsc_pps_infoframe_pack()
+ *
+ * Returns:
+ * Line buffer depth supported by DSC panel or 0 its invalid
+ */
 u8 drm_dp_dsc_sink_line_buf_depth(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
 {
 	u8 line_buf_depth = dsc_dpcd[DP_DSC_LINE_BUF_BIT_DEPTH - DP_DSC_SUPPORT];
@@ -1434,6 +1462,23 @@ u8 drm_dp_dsc_sink_line_buf_depth(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
 }
 EXPORT_SYMBOL(drm_dp_dsc_sink_line_buf_depth);
 
+/**
+ * drm_dp_dsc_sink_supported_input_bpcs() - Get all the input bits per component
+ * values supported by the DSC sink.
+ * @dsc_dpcd: DSC capabilities from DPCD
+ * @dsc_bpc: An array to be filled by this helper with supported
+ *           input bpcs.
+ *
+ * Read the DSC DPCD from the sink device to parse the supported bits per
+ * component values. This is used to populate the DSC parameters
+ * in the &struct drm_dsc_config by the driver.
+ * Driver creates an infoframe using these parameters to populate
+ * &struct drm_dsc_pps_infoframe. These are sent to the sink using DSC
+ * infoframe using the helper function drm_dsc_pps_infoframe_pack()
+ *
+ * Returns:
+ * Number of input BPC values parsed from the DPCD
+ */
 int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
 					 u8 dsc_bpc[3])
 {
diff --git a/drivers/gpu/drm/drm_dsc.c b/drivers/gpu/drm/drm_dsc.c
@@ -17,6 +17,12 @@
 /**
  * DOC: dsc helpers
  *
+ * VESA specification for DP 1.4 adds a new feature called Display Stream
+ * Compression (DSC) used to compress the pixel bits before sending it on
+ * DP/eDP/MIPI DSI interface. DSC is required to be enabled so that the existing
+ * display interfaces can support high resolutions at higher frames rates uisng
+ * the maximum available link capacity of these interfaces.
+ *
  * These functions contain some common logic and helpers to deal with VESA
  * Display Stream Compression standard required for DSC on Display Port/eDP or
  * MIPI display interfaces.
@@ -26,6 +32,13 @@
  * drm_dsc_dp_pps_header_init() - Initializes the PPS Header
  * for DisplayPort as per the DP 1.4 spec.
  * @pps_sdp: Secondary data packet for DSC Picture Parameter Set
+ *           as defined in &struct drm_dsc_pps_infoframe
+ *
+ * DP 1.4 spec defines the secondary data packet for sending the
+ * picture parameter infoframes from the source to the sink.
+ * This function populates the pps header defined in
+ * &struct drm_dsc_pps_infoframe as per the header bytes defined
+ * in &struct dp_sdp_header.
  */
 void drm_dsc_dp_pps_header_init(struct drm_dsc_pps_infoframe *pps_sdp)
 {
@@ -38,15 +51,20 @@ EXPORT_SYMBOL(drm_dsc_dp_pps_header_init);
 
 /**
  * drm_dsc_pps_infoframe_pack() - Populates the DSC PPS infoframe
- * using the DSC configuration parameters in the order expected
- * by the DSC Display Sink device. For the DSC, the sink device
- * expects the PPS payload in the big endian format for the fields
- * that span more than 1 byte.
  *
  * @pps_sdp:
- * Secondary data packet for DSC Picture Parameter Set
+ * Secondary data packet for DSC Picture Parameter Set. This is defined
+ * by &struct drm_dsc_pps_infoframe
  * @dsc_cfg:
- * DSC Configuration data filled by driver
+ * DSC Configuration data filled by driver as defined by
+ * &struct drm_dsc_config
+ *
+ * DSC source device sends a secondary data packet filled with all the
+ * picture parameter set (PPS) information required by the sink to decode
+ * the compressed frame. Driver populates the dsC PPS infoframe using the DSC
+ * configuration parameters in the order expected by the DSC Display Sink
+ * device. For the DSC, the sink device expects the PPS payload in the big
+ * endian format for the fields that span more than 1 byte.
  */
 void drm_dsc_pps_infoframe_pack(struct drm_dsc_pps_infoframe *pps_sdp,
 				const struct drm_dsc_config *dsc_cfg)
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
@@ -1052,11 +1052,18 @@ int drm_dp_bw_code_to_link_rate(u8 link_bw);
 #define DP_SDP_VSC_EXT_CEA		0x21 /* DP 1.4 */
 /* 0x80+ CEA-861 infoframe types */
 
+/**
+ * struct dp_sdp_header - DP secondary data packet header
+ * @HB0: Secondary Data Packet ID
+ * @HB1: Secondary Data Packet Type
+ * @HB2: Secondary Data Packet Specific header, Byte 0
+ * @HB3: Secondary Data packet Specific header, Byte 1
+ */
 struct dp_sdp_header {
-	u8 HB0; /* Secondary Data Packet ID */
-	u8 HB1; /* Secondary Data Packet Type */
-	u8 HB2; /* Secondary Data Packet Specific header, Byte 0 */
-	u8 HB3; /* Secondary Data packet Specific header, Byte 1 */
+	u8 HB0;
+	u8 HB1;
+	u8 HB2;
+	u8 HB3;
 } __packed;
 
 #define EDP_SDP_HEADER_REVISION_MASK		0x1F
diff --git a/include/drm/drm_dsc.h b/include/drm/drm_dsc.h
