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@xxxxxxxxx>
Suggested-by: Sean Paul <sean@xxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Sean Paul <sean@xxxxxxxxxx>
Signed-off-by: Manasi Navare <manasi.d.navare@xxxxxxxxx>
Acked-by: Sean Paul <sean@xxxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
drivers/gpu/drm/drm_dp_helper.c | 47 ++++++-
drivers/gpu/drm/drm_dsc.c | 30 +++-
include/drm/drm_dp_helper.h | 15 +-
include/drm/drm_dsc.h | 233 ++++++++++++++++++++++++--------
4 files changed, 259 insertions(+), 66 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 54120b6319e7..54a6414c5d96 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 +1418,21 @@ 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
index bc2b23adb072..bce99f95c1a3 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 +32,13 @@
* 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
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..9c26f083c70f 100644
--- a/include/drm/drm_dsc.h
+++ b/include/drm/drm_dsc.h
@@ -44,111 +44,231 @@
#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
+ *
+ * This defines different rate control parameters used by the DSC engine
+ * to compress the frame.
+ */
struct drm_dsc_rc_range_parameters {
- /* Min Quantization Parameters allowed for this range */
+ /**
+ * @range_min_qp: Min Quantization Parameters allowed for this range
+ */
u8 range_min_qp;
- /* Max Quantization Parameters allowed for this range */
+ /**
+ * @range_max_qp: Max Quantization Parameters allowed for this range
+ */
u8 range_max_qp;
- /* Bits/group offset to apply to target for this group */
+ /**
+ * @range_bpg_offset:
+ * Bits/group offset to apply to target for this group
+ */
u8 range_bpg_offset;
};
+/**
+ * struct drm_dsc_config - Parameters required to configure DSC
+ *
+ * Driver populates this structure with all the parameters required
+ * to configure the display stream compression on the source.
+ */
struct drm_dsc_config {
- /* Bits / component for previous reconstructed line buffer */
+ /**
+ * @line_buf_depth:
+ * Bits per component for previous reconstructed line buffer
+ */
u8 line_buf_depth;
- /* Bits per component to code (must be 8, 10, or 12) */
+ /**
+ * @bits_per_component: Bits per component to code (8/10/12)
+ */
u8 bits_per_component;
- /*
- * Flag indicating to do RGB - YCoCg conversion
- * and back (should be 1 for RGB input)
+ /**
+ * @convert_rgb:
+ * Flag to indicate if RGB - YCoCg conversion is needed
+ * True if RGB input, False if YCoCg input
*/
bool convert_rgb;
+ /**
+ * @slice_count: Number fo slices per line used by the DSC encoder
+ */
u8 slice_count;
- /* Slice Width */
+ /**
+ * @slice_width: Width of each slice in pixels
+ */
u16 slice_width;
- /* Slice Height */
+ /**
+ * @slice_height: Slice height in pixels
+ */
u16 slice_height;
- /*
- * 4:2:2 enable mode (from PPS, 4:2:2 conversion happens
- * outside of DSC encode/decode algorithm)
+ /**
+ * @enable422: True for 4_2_2 sampling, false for 4_4_4 sampling
*/
bool enable422;
- /* Picture Width */
+ /**
+ * @pic_width: Width of the input display frame in pixels
+ */
u16 pic_width;
- /* Picture Height */
+ /**
+ * @pic_height: Vertical height of the input display frame
+ */
u16 pic_height;
- /* Offset to bits/group used by RC to determine QP adjustment */
+ /**
+ * @rc_tgt_offset_high:
+ * 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 */
+ /**
+ * @rc_tgt_offset_low:
+ * Offset to bits/group used by RC to determine QP adjustment
+ */
u8 rc_tgt_offset_low;
- /* Bits/pixel target << 4 (ie., 4 fractional bits) */
+ /**
+ * @bits_per_pixel:
+ * Target bits per pixel with 4 fractional bits, bits_per_pixel << 4
+ */
u16 bits_per_pixel;
- /*
- * Factor to determine if an edge is present based
- * on the bits produced
+ /**
+ * @rc_edge_factor:
+ * 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 */
+ /**
+ * @rc_quant_incr_limit1:
+ * Slow down incrementing once the range reaches this value
+ */
u8 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
+ */
u8 rc_quant_incr_limit0;
- /* Number of pixels to delay the initial transmission */
+ /**
+ * @initial_xmit_delay:
+ * 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 */
+ /**
+ * @initial_dec_delay:
+ * Initial decoder delay, number of pixel times that the decoder
+ * accumulates data in its rate buffer before starting to decode
+ * and output pixels.
+ */
u16 initial_dec_delay;
- /* Block prediction enable */
+ /**
+ * @block_pred_enable:
+ * True if block prediction is used to code any groups within the
+ * picture. False if BP not used
+ */
bool block_pred_enable;
- /* Bits/group offset to use for first line of the slice */
+ /**
+ * @first_line_bpg_offset:
+ * Number of additional bits allocated for each group on the first
+ * line of slice.
+ */
u8 first_line_bpg_offset;
- /* Value to use for RC model offset at slice start */
+ /**
+ * @initial_offset: Value to use for RC model offset at slice start
+ */
u16 initial_offset;
- /* Thresholds defining each of the buffer ranges */
+ /**
+ * @rc_buf_thresh: Thresholds defining each of the buffer ranges
+ */
u16 rc_buf_thresh[DSC_NUM_BUF_RANGES - 1];
- /* Parameters for each of the RC ranges */
+ /**
+ * @rc_range_params:
+ * Parameters for each of the RC ranges defined in
+ * &struct drm_dsc_rc_range_parameters
+ */
struct drm_dsc_rc_range_parameters rc_range_params[DSC_NUM_BUF_RANGES];
- /* Total size of RC model */
+ /**
+ * @rc_model_size: Total size of RC model
+ */
u16 rc_model_size;
- /* Minimum QP where flatness information is sent */
+ /**
+ * @flatness_min_qp: Minimum QP where flatness information is sent
+ */
u8 flatness_min_qp;
- /* Maximum QP where flatness information is sent */
+ /**
+ * @flatness_max_qp: Maximum QP where flatness information is sent
+ */
u8 flatness_max_qp;
- /* Initial value for scale factor */
+ /**
+ * @initial_scale_value: Initial value for the scale factor
+ */
u8 initial_scale_value;
- /* Decrement scale factor every scale_decrement_interval groups */
+ /**
+ * @scale_decrement_interval:
+ * Specifies number of group times between decrementing the scale factor
+ * at beginning of a slice.
+ */
u16 scale_decrement_interval;
- /* Increment scale factor every scale_increment_interval groups */
+ /**
+ * @scale_increment_interval:
+ * Number of group times between incrementing the scale factor value
+ * used at the beginning of a slice.
+ */
u16 scale_increment_interval;
- /* Non-first line BPG offset to use */
+ /**
+ * @nfl_bpg_offset: Non first line BPG offset to be used
+ */
u16 nfl_bpg_offset;
- /* BPG offset used to enforce slice bit */
+ /**
+ * @slice_bpg_offset: BPG offset used to enforce slice bit
+ */
u16 slice_bpg_offset;
- /* Final RC linear transformation offset value */
+ /**
+ * @final_offset: Final RC linear transformation offset value
+ */
u16 final_offset;
- /* Enable on-off VBR (ie., disable stuffing bits) */
+ /**
+ * @vbr_enable: True if VBR mode is enabled, false if disabled
+ */
bool vbr_enable;
- /* Mux word size (in bits) for SSM mode */
+ /**
+ * @mux_word_size: 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
+ /**
+ * @slice_chunk_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 */
+ /**
+ * @rc_bits: Rate control buffer size in bits
+ */
u16 rc_bits;
- /* DSC Minor Version */
+ /**
+ * @dsc_version_minor: DSC minor version
+ */
u8 dsc_version_minor;
- /* DSC Major version */
+ /**
+ * @dsc_version_major: DSC major version
+ */
u8 dsc_version_major;
- /* Native 4:2:2 support */
+ /**
+ * @native_422: True if Native 4:2:2 supported, else false
+ */
bool native_422;
- /* Native 4:2:0 support */
+ /**
+ * @native_420: True if Native 4:2:0 supported else false.
+ */
bool native_420;
- /* Additional bits/grp for seconnd line of slice for native 4:2:0 */
+ /**
+ * @second_line_bpg_offset:
+ * 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 */
+ /**
+ * @nsl_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 */
+ /**
+ * @second_line_offset_adj:
+ * Offset adjustment for second line in Native 4:2:0 mode
+ */
u16 second_line_offset_adj;
};
@@ -468,10 +588,13 @@ 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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