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

* [PATCH] drm/dsc: Add kernel documentation for DRM DP DSC helpers
@ 2019-02-04 23:40 Manasi Navare
  2019-02-04 23:46 ` ✗ Fi.CI.CHECKPATCH: warning for " Patchwork
                   ` (10 more replies)
  0 siblings, 11 replies; 16+ messages in thread
From: Manasi Navare @ 2019-02-04 23:40 UTC (permalink / raw)
  To: intel-gfx, dri-devel; +Cc: Manasi Navare, Daniel Vetter, Sean Paul

This patch adds appropiate 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.

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>
---
 drivers/gpu/drm/drm_dp_helper.c |  42 +++++++++-
 drivers/gpu/drm/drm_dsc.c       |  13 ++-
 include/drm/drm_dp_helper.h     |  15 +++-
 include/drm/drm_dsc.h           | 138 ++++++++++++++++++--------------
 4 files changed, 142 insertions(+), 66 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 54120b6319e7..e9e0233f5b2f 100644
--- 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 +1418,19 @@ 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 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()
+ * @dsc_dpcd: DSC capabilities from DPCD
+ *
+ * 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 +1460,20 @@ 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. 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()
+ * @dsc_dpcd: DSC capabilities from DPCD
+ * @dsc_bpc: An array to be filled by this helper with supported
+ *           input bpcs.
+ *
+ * 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
index bc2b23adb072..0fd56fbdf9b4 100644
--- 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 +32,7 @@
  * 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
  */
 void drm_dsc_dp_pps_header_init(struct drm_dsc_pps_infoframe *pps_sdp)
 {
@@ -44,9 +51,11 @@ EXPORT_SYMBOL(drm_dsc_dp_pps_header_init);
  * 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
  */
 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
index 5db7fb8c8b50..2711cdfa0c13 100644
--- 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
index d03f1b83421a..f50d265a97e2 100644
--- a/include/drm/drm_dsc.h
+++ b/include/drm/drm_dsc.h
@@ -44,111 +44,128 @@
 #define DSC_1_2_MAX_LINEBUF_DEPTH_VAL		0
 #define DSC_1_1_MAX_LINEBUF_DEPTH_BITS		13
 
-/* Configuration for a single Rate Control model range */
+/**
+ * struct drm_dsc_rc_range_parameters - DSC Rate Control range parameters
+ *
+ * @range_min_qp: Min Quantization Parameters allowed for this range
+ * @range_max_qp: Max Quantization Parameters allowed for this range
+ * @range_bpg_offset: Bits/group offset to apply to target for this group
+ */
 struct drm_dsc_rc_range_parameters {
-	/* Min Quantization Parameters allowed for this range */
 	u8 range_min_qp;
-	/* Max Quantization Parameters allowed for this range */
 	u8 range_max_qp;
-	/* Bits/group offset to apply to target for this group */
 	u8 range_bpg_offset;
 };
 
+/**
+ * struct drm_dsc_config - Parameters required to configure DSC
+ *
+ * @line_buf_depth: Bits / component for previous reconstructed line buffer
+ * @bits_per_component: Bits per component to code (8/10/12)
+ * @convert_rgb: Flag to indicate if RGB - YCoCg conversion is needed
+ *               True if RGB input, False if YCoCg input
+ * @slice_count: Number fo slices per line used by the DSC encoder
+ * @slice_width: Width of each slice in pixels
+ * @slice_height: Slice height in pixels
+ * @enable422: True for 4_2_2 sampling, false for 4_4_4 sampling
+ * @pic_width: Width of the input display frame in pixels
+ * @pic_height: Vertical height of the input display frame
+ * @rc_tgt_offset_high: Offset to bits/group used by RC to determine QP
+ *                      adjustment
+ * @rc_tgt_offset_low: Offset to bits/group used by RC to determine QP
+ *                     adjustment
+ * @bits_per_pixel: Target bits per pixel with 4 fractional bits.
+ *                  bits_per_pixel << 4
+ * @rc_edge_factor: Factor to determine if an edge is present based on the
+ *                  bits produced
+ * @rc_quant_incr_limit1: Slow down incrementing once the range reaches this
+ *                        value
+ * @rc_quant_incr_limit0: Slow down incrementing once the range reaches this
+ *                        value
+ * @initial_xmit_delay: Number of pixels to delay the initial transmission
+ * @initial_dec_delay: Initial decoder delay, number of pixel times that the
+ *                     decoer accumulates data in its rate buffer before
+ *                     starting to decode and output pixels.
+ * @block_pred_enable: True if block prediction is used to code any groups
+ *                     within the picture.
+ *                     False if BP not used
+ * @first_line_bpg_offset: Number of additional bits allocated for each group on
+ *                         the first line of slice.
+ * @initial_offset: Value to use for RC model offset at slice start
+ * @rc_buf_thresh: Thresholds defining each of the buffer ranges
+ * @rc_range_params: Parameters for each of the RC ranges defined in
+ *                   &struct drm_dsc_rc_range_parameters
+ * @rc_model_size: Total size of RC model
+ * @flatness_min_qp: Minimum QP where flatness information is sent
+ * @flatness_max_qp: Maximum QP where flatness information is sent
+ * @initial_scale_value: Initial value for the scale factor
+ * @scale_decrement_interval: Specifies number of group times between
+ *                            decrementing the scale factor at beginning
+ *                            of a slice.
+ * @scale_increment_interval: Number of group times between incrementing
+ *                            the scale factor value used at the beginning
+ *                            of a slice.
+ * @nfl_bpg_offset: Non first line BPG offset to be used
+ * @slice_bpg_offset: BPG offset used to enforce slice bit
+ * @final_offset: Final RC linear transformation offset value
+ * @vbr_enable: True if VBR mode is enabled, false if disabled
+ * @mux_word_size: Mux word size (in bits) for SSM mode
+ * @slice_chunk_size: The (max) size in bytes of the "chunks" that are
+ *                    used in slice multiplexing.
+ * @rc_bits: Rate control buffer size in bits
+ * @dsc_version_minor: DSC minor version
+ * @dsc_version_major: DSC major version
+ * @native_422: True if Native 4:2:2 supported, else false
+ * @native_420: True if Native 4:2:0 supported else false.
+ * @second_line_bpg_offset: Additional bits/grp for seconnd line of slice for
+ *                          native 4:2:0
+ * @nsl_bpg_offset: Num of bits deallocated for each grp that is not in second
+ *                  line of slice
+ * @second_line_offset_adj: Offset adjustment for second line in Native 4:2:0
+ *                          mode
+ */
 struct drm_dsc_config {
-	/* Bits / component for previous reconstructed line buffer */
 	u8 line_buf_depth;
-	/* Bits per component to code (must be 8, 10, or 12) */
 	u8 bits_per_component;
-	/*
-	 * Flag indicating to do RGB - YCoCg conversion
-	 * and back (should be 1 for RGB input)
-	 */
 	bool convert_rgb;
 	u8 slice_count;
-	/* Slice Width */
 	u16 slice_width;
-	/* Slice Height */
 	u16 slice_height;
-	/*
-	 * 4:2:2 enable mode (from PPS, 4:2:2 conversion happens
-	 * outside of DSC encode/decode algorithm)
-	 */
 	bool enable422;
-	/* Picture Width */
 	u16 pic_width;
-	/* Picture Height */
 	u16 pic_height;
-	/* Offset to bits/group used by RC to determine QP adjustment */
 	u8 rc_tgt_offset_high;
-	/* Offset to bits/group used by RC to determine QP adjustment */
 	u8 rc_tgt_offset_low;
-	/* Bits/pixel target << 4 (ie., 4 fractional bits) */
 	u16 bits_per_pixel;
-	/*
-	 * Factor to determine if an edge is present based
-	 * on the bits produced
-	 */
 	u8 rc_edge_factor;
-	/* Slow down incrementing once the range reaches this value */
 	u8 rc_quant_incr_limit1;
-	/* Slow down incrementing once the range reaches this value */
 	u8 rc_quant_incr_limit0;
-	/* Number of pixels to delay the initial transmission */
 	u16 initial_xmit_delay;
-	/* Number of pixels to delay the VLD on the decoder,not including SSM */
 	u16  initial_dec_delay;
-	/* Block prediction enable */
 	bool block_pred_enable;
-	/* Bits/group offset to use for first line of the slice */
 	u8 first_line_bpg_offset;
-	/* Value to use for RC model offset at slice start */
 	u16 initial_offset;
-	/* Thresholds defining each of the buffer ranges */
 	u16 rc_buf_thresh[DSC_NUM_BUF_RANGES - 1];
-	/* Parameters for each of the RC ranges */
 	struct drm_dsc_rc_range_parameters rc_range_params[DSC_NUM_BUF_RANGES];
-	/* Total size of RC model */
 	u16 rc_model_size;
-	/* Minimum QP where flatness information is sent */
 	u8 flatness_min_qp;
-	/* Maximum QP where flatness information is sent */
 	u8 flatness_max_qp;
-	/* Initial value for scale factor */
 	u8 initial_scale_value;
-	/* Decrement scale factor every scale_decrement_interval groups */
 	u16 scale_decrement_interval;
-	/* Increment scale factor every scale_increment_interval groups */
 	u16 scale_increment_interval;
-	/* Non-first line BPG offset to use */
 	u16 nfl_bpg_offset;
-	/* BPG offset used to enforce slice bit */
 	u16 slice_bpg_offset;
-	/* Final RC linear transformation offset value */
 	u16 final_offset;
-	/* Enable on-off VBR (ie., disable stuffing bits) */
 	bool vbr_enable;
-	/* Mux word size (in bits) for SSM mode */
 	u8 mux_word_size;
-	/*
-	 * The (max) size in bytes of the "chunks" that are
-	 * used in slice multiplexing
-	 */
 	u16 slice_chunk_size;
-	/* Rate Control buffer siz in bits */
 	u16 rc_bits;
-	/* DSC Minor Version */
 	u8 dsc_version_minor;
-	/* DSC Major version */
 	u8 dsc_version_major;
-	/* Native 4:2:2 support */
 	bool native_422;
-	/* Native 4:2:0 support */
 	bool native_420;
-	/* Additional bits/grp for seconnd line of slice for native 4:2:0 */
 	u8 second_line_bpg_offset;
-	/* Num of bits deallocated for each grp that is not in second line of slice */
 	u16 nsl_bpg_offset;
-	/* Offset adj fr second line in Native 4:2:0 mode */
 	u16 second_line_offset_adj;
 };
 
@@ -468,10 +485,13 @@ struct drm_dsc_picture_parameter_set {
  * This structure represents the DSC PPS infoframe required to send the Picture
  * Parameter Set metadata required before enabling VESA Display Stream
  * Compression. This is based on the DP Secondary Data Packet structure and
- * comprises of SDP Header as defined in drm_dp_helper.h and PPS payload.
+ * comprises of SDP Header as defined &struct struct dp_sdp_header in drm_dp_helper.h
+ * and PPS payload defined in &struct drm_dsc_picture_parameter_set.
  *
- * @pps_header: Header for PPS as per DP SDP header format
+ * @pps_header: Header for PPS as per DP SDP header format of type
+ *              &struct dp_sdp_header
  * @pps_payload: PPS payload fields as per DSC specification Table 4-1
+ *               as represented in &struct drm_dsc_picture_parameter_set
  */
 struct drm_dsc_pps_infoframe {
 	struct dp_sdp_header pps_header;
-- 
2.19.1

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