2.13.1. V4L2_META_FMT_MALI_C55_STATS (‘C55S’), V4L2_META_FMT_MALI_C55_PARAMS (‘C55P’)¶

2.13.1.1. 3A Statistics¶

The ISP device collects different statistics over an input bayer frame. Those statistics can be obtained by userspace from the mali-c55 3a stats metadata capture video node, using the v4l2_meta_format interface. The buffer contains a single instance of the C structure mali_c55_stats_buffer defined in mali-c55-config.h, so the structure can be obtained from the buffer by:

struct mali_c55_stats_buffer *stats =
        (struct mali_c55_stats_buffer *)buf;

For details of the statistics see mali_c55_stats_buffer.

2.13.1.2. Configuration Parameters¶

The configuration parameters are passed to the mali-c55 3a params metadata output video node, using the v4l2_meta_format interface. Rather than a single struct containing sub-structs for each configurable area of the ISP, parameters for the Mali-C55 use the v4l2-isp parameters system, through which groups of parameters are defined as distinct structs or “blocks” which may be added to the data member of v4l2_isp_params_buffer. Userspace is responsible for populating the data member with the blocks that need to be configured by the driver. Each block-specific struct embeds v4l2_isp_params_block_header as its first member and userspace must populate the type member with a value from mali_c55_param_block_type.

struct v4l2_isp_params_buffer *params =
        (struct v4l2_isp_params_buffer *)buffer;

params->version = MALI_C55_PARAM_BUFFER_V1;
params->data_size = 0;

void *data = (void *)params->data;

struct mali_c55_params_awb_gains *gains =
        (struct mali_c55_params_awb_gains *)data;

gains->header.type = MALI_C55_PARAM_BLOCK_AWB_GAINS;
gains->header.flags |= V4L2_ISP_PARAMS_FL_BLOCK_ENABLE;
gains->header.size = sizeof(struct mali_c55_params_awb_gains);

gains->gain00 = 256;
gains->gain00 = 256;
gains->gain00 = 256;
gains->gain00 = 256;

data += sizeof(struct mali_c55_params_awb_gains);
params->data_size += sizeof(struct mali_c55_params_awb_gains);

struct mali_c55_params_sensor_off_preshading *blc =
        (struct mali_c55_params_sensor_off_preshading *)data;

blc->header.type = MALI_C55_PARAM_BLOCK_SENSOR_OFFS;
blc->header.flags |= V4L2_ISP_PARAMS_FL_BLOCK_ENABLE;
blc->header.size = sizeof(struct mali_c55_params_sensor_off_preshading);

blc->chan00 = 51200;
blc->chan01 = 51200;
blc->chan10 = 51200;
blc->chan11 = 51200;

params->data_size += sizeof(struct mali_c55_params_sensor_off_preshading);

2.13.1.3. Arm Mali-C55 uAPI data types¶

struct mali_c55_ae_1024bin_hist¶: Auto Exposure 1024-bin histogram statistics

Definition:

struct mali_c55_ae_1024bin_hist {
    __u16 bins[1024];
};

Members

bins: 1024 element array of 16-bit pixel counts.

Description

The 1024-bin histogram module collects image-global but zone-weighted intensity distributions of pixels in fixed-width bins. The modules can be configured into different “plane modes” which affect the contents of the collected statistics. In plane mode 0, pixel intensities are taken regardless of colour plane into a single 1024-bin histogram with a bin width of 4. In plane mode 1, four 256-bin histograms with a bin width of 16 are collected - one for each CFA colour plane. In plane modes 4, 5, 6 and 7 two 512-bin histograms with a bin width of 8 are collected - in each mode one of the colour planes is collected into the first histogram and all the others are combined into the second. The histograms are stored consecutively in the bins array.

The 16-bit pixel counts are stored as a 4-bit exponent in the most significant bits followed by a 12-bit mantissa. Conversion to a usable format can be done according to the following pseudo-code:

if (e == 0) {
        bin = m * 2;
} else {
        bin = (m + 4096) * 2^e
}

where: e is the exponent value in range 0..15 m is the mantissa value in range 0..4095

The pixels used in calculating the statistics can be masked using three methods:

Pixels can be skipped in X and Y directions independently.
Minimum/Maximum intensities can be configured
Zones can be differentially weighted, including 0 weighted to mask them

The data for this histogram can be collected from different tap points in the ISP depending on configuration - after the white balance or digital gain blocks, or immediately after the input crossbar.

struct mali_c55_ae_5bin_hist¶: Auto Exposure 5-bin histogram statistics

Definition:

struct mali_c55_ae_5bin_hist {
    __u16 hist0;
    __u16 hist1;
    __u16 hist3;
    __u16 hist4;
};

Members

hist0: 16-bit normalised pixel count for the 0th intensity bin
hist1: 16-bit normalised pixel count for the 1st intensity bin
hist3: 16-bit normalised pixel count for the 3rd intensity bin
hist4: 16-bit normalised pixel count for the 4th intensity bin

Description

The ISP generates a 5-bin histogram of normalised pixel counts within bins of pixel intensity for each of 225 possible zones within a frame. The centre bin of the histogram for each zone is not available from the hardware and must be calculated by subtracting the values of hist0, hist1, hist3 and hist4 from 0xffff as in the following equation:

hist2 = 0xffff - (hist0 + hist1 + hist3 + hist4)

struct mali_c55_awb_average_ratios¶: Auto White Balance colour ratios

Definition:

struct mali_c55_awb_average_ratios {
    __u16 avg_rg_gr;
    __u16 avg_bg_br;
    __u32 num_pixels;
};

Members

avg_rg_gr: Average R/G or G/R ratio in Q4.8 format.
avg_bg_br: Average B/G or B/R ratio in Q4.8 format.
num_pixels: The number of pixels used in the AWB calculation

Description

The ISP calculates and collects average colour ratios for each zone in an image and stores them in Q4.8 format (the lowest 8 bits are fractional, with bits [11:8] representing the integer). The exact ratios collected (either R/G, B/G or G/R, B/R) are configurable through the parameters buffer. The value of the 4 high bits is undefined.

struct mali_c55_af_statistics¶: Auto Focus edge and intensity statistics

Definition:

struct mali_c55_af_statistics {
    __u16 intensity_stats;
    __u16 edge_stats;
};

Members

intensity_stats: Packed mantissa and exponent value for pixel intensity
edge_stats: Packed mantissa and exponent values for edge intensity

Description

The ISP collects the squared sum of pixel intensities for each zone within a configurable Region of Interest on the frame. Additionally, the same data are collected after being passed through a bandpass filter which removes high and low frequency components - these are referred to as the edge statistics.

The intensity and edge statistics for a zone can be used to calculate the contrast information for a zone

C = E2 / I2

Where I2 is the intensity statistic for a zone and E2 is the edge statistic for that zone. Optimum focus is reached when C is at its maximum.

The intensity and edge statistics are stored packed into a non-standard 16 bit floating point format, where the 7 most significant bits represent the exponent and the 9 least significant bits the mantissa. This format can be unpacked with the following pseudocode:

if (e == 0) {
        x = m;
} else {
        x = 2^e-1 * (m + 2^9)
}

where: e is the exponent value in range 0..127 m is the mantissa value in range 0..511

struct mali_c55_stats_buffer¶: 3A statistics for the mali-c55 ISP

Definition:

struct mali_c55_stats_buffer {
    struct mali_c55_ae_1024bin_hist ae_1024bin_hist;
    struct mali_c55_ae_1024bin_hist iridix_1024bin_hist;
    struct mali_c55_ae_5bin_hist ae_5bin_hists[MALI_C55_MAX_ZONES];
    __u32 reserved1[14];
    struct mali_c55_awb_average_ratios awb_ratios[MALI_C55_MAX_ZONES];
    __u32 reserved2[14];
    struct mali_c55_af_statistics af_statistics[MALI_C55_MAX_ZONES];
    __u32 reserved3[15];
};

Members

ae_1024bin_hist: 1024-bin frame-global pixel intensity histogram
iridix_1024bin_hist: Post-Iridix block 1024-bin histogram
ae_5bin_hists: 5-bin pixel intensity histograms for AEC
reserved1: Undefined buffer space
awb_ratios: Color balance ratios for Auto White Balance
reserved2: Undefined buffer space
af_statistics: Pixel intensity statistics for Auto Focus
reserved3: Undefined buffer space

Description

This struct describes the metering statistics space in the Mali-C55 ISP’s hardware in its entirety. The space between each defined area is marked as “unknown” and may not be 0, but should not be used. The ae_5bin_hists, awb_ratios and af_statistics members are arrays of statistics per-zone. The zones are arranged in the array in raster order starting from the top left corner of the image.

enum mali_c55_param_buffer_version¶: Mali-C55 parameters block versioning

Constants

MALI_C55_PARAM_BUFFER_V1: First version of Mali-C55 parameters block

enum mali_c55_param_block_type¶: Enumeration of Mali-C55 parameter blocks

Constants

MALI_C55_PARAM_BLOCK_SENSOR_OFFS: Sensor pre-shading black level offset
MALI_C55_PARAM_BLOCK_AEXP_HIST: Auto-exposure 1024-bin histogram configuration
MALI_C55_PARAM_BLOCK_AEXP_IHIST: Post-Iridix auto-exposure 1024-bin histogram configuration
MALI_C55_PARAM_BLOCK_AEXP_HIST_WEIGHTS: Auto-exposure 1024-bin histogram weighting
MALI_C55_PARAM_BLOCK_AEXP_IHIST_WEIGHTS: Post-Iridix auto-exposure 1024-bin histogram weighting
MALI_C55_PARAM_BLOCK_DIGITAL_GAIN: Digital gain
MALI_C55_PARAM_BLOCK_AWB_GAINS: Auto-white balance gains
MALI_C55_PARAM_BLOCK_AWB_CONFIG: Auto-white balance statistics config
MALI_C55_PARAM_BLOCK_AWB_GAINS_AEXP: Auto-white balance gains for AEXP-0 tap
MALI_C55_PARAM_MESH_SHADING_CONFIG: Mesh shading tables configuration
MALI_C55_PARAM_MESH_SHADING_SELECTION: Mesh shading table selection

Description

This enumeration defines the types of Mali-C55 parameters block. Each block configures a specific processing block of the Mali-C55 ISP. The block type allows the driver to correctly interpret the parameters block data.

It is the responsibility of userspace to correctly set the type of each parameters block.

struct mali_c55_params_sensor_off_preshading¶: offset subtraction for each color channel

Definition:

struct mali_c55_params_sensor_off_preshading {
    struct v4l2_isp_params_block_header header;
    __u32 chan00;
    __u32 chan01;
    __u32 chan10;
    __u32 chan11;
};

Members

header: The Mali-C55 parameters block header
chan00: Offset for color channel 00 (default: R)
chan01: Offset for color channel 01 (default: Gr)
chan10: Offset for color channel 10 (default: Gb)
chan11: Offset for color channel 11 (default: B)

Description

Provides removal of the sensor black level from the sensor data. Separate offsets are provided for each of the four Bayer component color channels which are defaulted to R, Gr, Gb, B.

header.type should be set to MALI_C55_PARAM_BLOCK_SENSOR_OFFS from mali_c55_param_block_type for this block.

enum mali_c55_aexp_hist_tap_points¶: Tap points for the AEXP histogram

Constants

MALI_C55_AEXP_HIST_TAP_WB: After static white balance
MALI_C55_AEXP_HIST_TAP_FS: After WDR Frame Stitch
MALI_C55_AEXP_HIST_TAP_TPG: After the test pattern generator

enum mali_c55_aexp_skip_x¶: Horizontal pixel skipping

Constants

MALI_C55_AEXP_SKIP_X_EVERY_2ND: Collect every 2nd pixel horizontally
MALI_C55_AEXP_SKIP_X_EVERY_3RD: Collect every 3rd pixel horizontally
MALI_C55_AEXP_SKIP_X_EVERY_4TH: Collect every 4th pixel horizontally
MALI_C55_AEXP_SKIP_X_EVERY_5TH: Collect every 5th pixel horizontally
MALI_C55_AEXP_SKIP_X_EVERY_8TH: Collect every 8th pixel horizontally
MALI_C55_AEXP_SKIP_X_EVERY_9TH: Collect every 9th pixel horizontally

enum mali_c55_aexp_skip_y¶: Vertical pixel skipping

Constants

MALI_C55_AEXP_SKIP_Y_ALL: Collect every single pixel vertically
MALI_C55_AEXP_SKIP_Y_EVERY_2ND: Collect every 2nd pixel vertically
MALI_C55_AEXP_SKIP_Y_EVERY_3RD: Collect every 3rd pixel vertically
MALI_C55_AEXP_SKIP_Y_EVERY_4TH: Collect every 4th pixel vertically
MALI_C55_AEXP_SKIP_Y_EVERY_5TH: Collect every 5th pixel vertically
MALI_C55_AEXP_SKIP_Y_EVERY_8TH: Collect every 8th pixel vertically
MALI_C55_AEXP_SKIP_Y_EVERY_9TH: Collect every 9th pixel vertically

enum mali_c55_aexp_row_column_offset¶: Start from the first or second row or column

Constants

MALI_C55_AEXP_FIRST_ROW_OR_COL: Start from the first row / column
MALI_C55_AEXP_SECOND_ROW_OR_COL: Start from the second row / column

enum mali_c55_aexp_hist_plane_mode¶: Mode for the AEXP Histograms

Constants

MALI_C55_AEXP_HIST_COMBINED: All color planes in one 1024-bin histogram
MALI_C55_AEXP_HIST_SEPARATE: Each color plane in one 256-bin histogram with a bin width of 16
MALI_C55_AEXP_HIST_FOCUS_00: Top left plane in the first bank, rest in second bank
MALI_C55_AEXP_HIST_FOCUS_01: Top right plane in the first bank, rest in second bank
MALI_C55_AEXP_HIST_FOCUS_10: Bottom left plane in the first bank, rest in second bank
MALI_C55_AEXP_HIST_FOCUS_11: Bottom right plane in the first bank, rest in second bank

Description

In the “focus” modes statistics are collected into two 512-bin histograms with a bin width of 8. One colour plane is in the first histogram with the remainder combined into the second. The four options represent which of the four positions in a bayer pattern are the focused plane.

struct mali_c55_params_aexp_hist¶: configuration for AEXP metering hists

Definition:

struct mali_c55_params_aexp_hist {
    struct v4l2_isp_params_block_header header;
    __u8 skip_x;
    __u8 offset_x;
    __u8 skip_y;
    __u8 offset_y;
    __u8 scale_bottom;
    __u8 scale_top;
    __u8 plane_mode;
    __u8 tap_point;
};

Members

header: The Mali-C55 parameters block header
skip_x: Horizontal decimation. See enum mali_c55_aexp_skip_x
offset_x: Skip the first column, or not. See enum mali_c55_aexp_row_column_offset
skip_y: Vertical decimation. See enum mali_c55_aexp_skip_y
offset_y: Skip the first row, or not. See enum mali_c55_aexp_row_column_offset
scale_bottom: Scale pixels in bottom half of intensity range: 0=1x ,1=2x, 2=4x, 4=8x, 4=16x
scale_top: scale pixels in top half of intensity range: 0=1x ,1=2x, 2=4x, 4=8x, 4=16x
plane_mode: Plane separation mode. See enum mali_c55_aexp_hist_plane_mode
tap_point: Tap point for histogram from enum mali_c55_aexp_hist_tap_points. This parameter is unused for the post-Iridix Histogram

Description

This struct allows users to configure the 1024-bin AEXP histograms. Broadly speaking the parameters allow you to mask particular regions of the image and to select different kinds of histogram.

The skip_x, offset_x, skip_y and offset_y fields allow users to ignore or mask pixels in the frame by their position relative to the top left pixel. First, the skip_y, offset_x and offset_y fields define which of the pixels within each 2x2 region will be counted in the statistics.

If skip_y == 0 then two pixels from each covered region will be counted. If both offset_x and offset_y are zero, then the two left-most pixels in each 2x2 pixel region will be counted. Setting offset_x = 1 will discount the top left pixel and count the top right pixel. Setting offset_y = 1 will discount the bottom left pixel and count the bottom right pixel.

If skip_y != 0 then only a single pixel from each region covered by the pattern will be counted. In this case offset_x controls whether the pixel that’s counted is in the left (if offset_x == 0) or right (if offset_x == 1) column and offset_y controls whether the pixel that’s counted is in the top (if offset_y == 0) or bottom (if offset_y == 1) row.

The skip_x and skip_y fields control how the 2x2 pixel region is repeated across the image data. The first instance of the region is always in the top left of the image data. The skip_x field controls how many pixels are ignored in the x direction before the pixel masking region is repeated. The skip_y field controls how many pixels are ignored in the y direction before the pixel masking region is repeated.

These fields can be used to reduce the number of pixels counted for the statistics, but it’s important to be careful to configure them correctly. Some combinations of values will result in colour components from the input data being ignored entirely, for example in the following configuration:

skip_x = 0 offset_x = 0 skip_y = 0 offset_y = 0

Only the R and Gb components of RGGB data that was input would be collected. Similarly in the following configuration:

skip_x = 0 offset_x = 0 skip_y = 1 offset_y = 1

Only the Gb component of RGGB data that was input would be collected. To correct things such that all 4 colour components were included it would be necessary to set the skip_x and skip_y fields in a way that resulted in all four colour components being collected:

skip_x = 1 offset_x = 0 skip_y = 1 offset_y = 1

header.type should be set to one of either MALI_C55_PARAM_BLOCK_AEXP_HIST or MALI_C55_PARAM_BLOCK_AEXP_IHIST from mali_c55_param_block_type.

struct mali_c55_params_aexp_weights¶: Array of weights for AEXP metering

Definition:

struct mali_c55_params_aexp_weights {
    struct v4l2_isp_params_block_header header;
    __u8 nodes_used_horiz;
    __u8 nodes_used_vert;
    __u8 zone_weights[MALI_C55_MAX_ZONES];
};

Members

header: The Mali-C55 parameters block header
nodes_used_horiz: Number of active zones horizontally [0..15]
nodes_used_vert: Number of active zones vertically [0..15]
zone_weights: Zone weighting. Index is row*col where 0,0 is the top left zone continuing in raster order. Each zone can be weighted in the range [0..15]. The number of rows and columns is defined by nodes_used_vert and nodes_used_horiz

Description

This struct allows users to configure the weighting for both of the 1024-bin AEXP histograms. The pixel data collected for each zone is multiplied by the corresponding weight from this array, which may be zero if the intention is to mask off the zone entirely.

header.type should be set to one of either MALI_C55_PARAM_BLOCK_AEXP_HIST_WEIGHTS or MALI_C55_PARAM_BLOCK_AEXP_IHIST_WEIGHTS from mali_c55_param_block_type.

struct mali_c55_params_digital_gain¶: Digital gain value

Definition:

struct mali_c55_params_digital_gain {
    struct v4l2_isp_params_block_header header;
    __u16 gain;
};

Members

header: The Mali-C55 parameters block header
gain: The digital gain value to apply, in Q5.8 format.

Description

This struct carries a digital gain value to set in the ISP.

header.type should be set to MALI_C55_PARAM_BLOCK_DIGITAL_GAIN from mali_c55_param_block_type for this block.

enum mali_c55_awb_stats_mode¶: Statistics mode for AWB

Constants

MALI_C55_AWB_MODE_GRBR: Statistics collected as Green/Red and Blue/Red ratios
MALI_C55_AWB_MODE_RGBG: Statistics collected as Red/Green and Blue/Green ratios

struct mali_c55_params_awb_gains¶: Gain settings for auto white balance

Definition:

struct mali_c55_params_awb_gains {
    struct v4l2_isp_params_block_header header;
    __u16 gain00;
    __u16 gain01;
    __u16 gain10;
    __u16 gain11;
};

Members

header: The Mali-C55 parameters block header
gain00: Multiplier for colour channel 00
gain01: Multiplier for colour channel 01
gain10: Multiplier for colour channel 10
gain11: Multiplier for colour channel 11

Description

This struct allows users to configure the gains for auto-white balance. There are four gain settings corresponding to each colour channel in the bayer domain. Although named generically, the association between the gain applied and the colour channel is done automatically within the ISP depending on the input format, and so the following mapping always holds true:

gain00 = R
gain01 = Gr
gain10 = Gb
gain11 = B

All of the gains are stored in Q4.8 format.

header.type should be set to one of either MALI_C55_PARAM_BLOCK_AWB_GAINS or MALI_C55_PARAM_BLOCK_AWB_GAINS_AEXP from mali_c55_param_block_type.

enum mali_c55_params_awb_tap_points¶: Tap points for the AWB statistics

Constants

MALI_C55_AWB_STATS_TAP_PF: Immediately after the Purple Fringe block
MALI_C55_AWB_STATS_TAP_CNR: Immediately after the CNR block

struct mali_c55_params_awb_config¶: Stats settings for auto-white balance

Definition:

struct mali_c55_params_awb_config {
    struct v4l2_isp_params_block_header header;
    __u8 tap_point;
    __u8 stats_mode;
    __u16 white_level;
    __u16 black_level;
    __u16 cr_max;
    __u16 cr_min;
    __u16 cb_max;
    __u16 cb_min;
    __u8 nodes_used_horiz;
    __u8 nodes_used_vert;
    __u16 cr_high;
    __u16 cr_low;
    __u16 cb_high;
    __u16 cb_low;
};

Members

header: The Mali-C55 parameters block header
tap_point: The tap point from enum mali_c55_params_awb_tap_points
stats_mode: AWB statistics collection mode, see mali_c55_awb_stats_mode
white_level: Upper pixel intensity (I.E. raw pixel values) limit
black_level: Lower pixel intensity (I.E. raw pixel values) limit
cr_max: Maximum R/G ratio (Q4.8 format)
cr_min: Minimum R/G ratio (Q4.8 format)
cb_max: Maximum B/G ratio (Q4.8 format)
cb_min: Minimum B/G ratio (Q4.8 format)
nodes_used_horiz: Number of active zones horizontally [0..15]
nodes_used_vert: Number of active zones vertically [0..15]
cr_high: R/G ratio trim high (Q4.8 format)
cr_low: R/G ratio trim low (Q4.8 format)
cb_high: B/G ratio trim high (Q4.8 format)
cb_low: B/G ratio trim low (Q4.8 format)

Description

This struct allows the configuration of the statistics generated for auto white balance. Pixel intensity limits can be set to exclude overly bright or dark regions of an image from the statistics entirely. Colour ratio minima and maxima can be set to discount pixels who’s ratios fall outside the defined boundaries; there are two sets of registers to do this - the “min/max” ratios which bound a region and the “high/low” ratios which further trim the upper and lower ratios. For example with the boundaries configured as follows, only pixels whos colour ratios falls into the region marked “A” would be counted:

                                                         cr_high
   2.0 |                                                   |
       |               cb_max --> _________________________v_____
   1.8 |                         |                         \    |
       |                         |                          \   |
   1.6 |                         |                           \  |
       |                         |                            \ |
c  1.4 |               cb_low -->|\              A             \|<--  cb_high
b      |                         | \                            |
   1.2 |                         |  \                           |
r      |                         |   \                          |
a  1.0 |              cb_min --> |____\_________________________|
t      |                         ^    ^                         ^
i  0.8 |                         |    |                         |
o      |                      cr_min  |                       cr_max
s  0.6 |                              |
       |                             cr_low
   0.4 |
       |
   0.2 |
       |
   0.0 |_______________________________________________________________
       0.0   0.2   0.4   0.6   0.8   1.0   1.2   1.4   1.6   1.8   2.0
                                  cr ratios

header.type should be set to MALI_C55_PARAM_BLOCK_AWB_CONFIG from mali_c55_param_block_type for this block.

struct mali_c55_params_mesh_shading_config¶: Mesh shading configuration

Definition:

struct mali_c55_params_mesh_shading_config {
    struct v4l2_isp_params_block_header header;
    __u8 mesh_show;
    __u8 mesh_scale;
    __u8 mesh_page_r;
    __u8 mesh_page_g;
    __u8 mesh_page_b;
    __u8 mesh_width;
    __u8 mesh_height;
    __u32 mesh[MALI_C55_NUM_MESH_SHADING_ELEMENTS];
};

Members

header: The Mali-C55 parameters block header
mesh_show: Output the mesh data rather than image data
mesh_scale: Set the precision and maximum gain range of mesh shading - 0 = 0-2x gain - 1 = 0-4x gain - 2 = 0-8x gain - 3 = 0-16x gain - 4 = 1-2x gain - 5 = 1-3x gain - 6 = 1-5x gain - 7 = 1-9x gain
mesh_page_r: Mesh page select for red colour plane [0..2]
mesh_page_g: Mesh page select for green colour plane [0..2]
mesh_page_b: Mesh page select for blue colour plane [0..2]
mesh_width: Number of horizontal nodes minus 1 [15,31]
mesh_height: Number of vertical nodes minus 1 [15,31]
mesh: Mesh shading correction tables

Description

The mesh shading correction module allows programming a separate table of either 16x16 or 32x32 node coefficients for 3 different light sources. The final correction coefficients applied are computed by blending the coefficients from two tables together.

A page of 1024 32-bit integers is associated to each colour channel, with pages stored consecutively in memory. Each 32-bit integer packs 3 8-bit correction coefficients for a single node, one for each of the three light sources. The 8 most significant bits are unused. The following table describes the layout:

+----------- Page (Colour Plane) 0 -------------+
| @mesh[i]  | Mesh Point | Bits  | Light Source |
+-----------+------------+-------+--------------+
|         0 |        0,0 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+-----------+------------+-------+--------------+
|         1 |        0,1 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+-----------+------------+-------+--------------+
|       ... |        ... | ...   | ...          |
+-----------+------------+-------+--------------+
|      1023 |      31,31 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+----------- Page (Colour Plane) 1 -------------+
| @mesh[i]  | Mesh Point | Bits  | Light Source |
+-----------+------------+-------+--------------+
|      1024 |        0,0 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+-----------+------------+-------+--------------+
|      1025 |        0,1 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+-----------+------------+-------+--------------+
|       ... |        ... | ...   | ...          |
+-----------+------------+-------+--------------+
|      2047 |      31,31 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+----------- Page (Colour Plane) 2 -------------+
| @mesh[i]  | Mesh Point | Bits  | Light Source |
+-----------+------------+-------+--------------+
|      2048 |        0,0 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+-----------+------------+-------+--------------+
|      2049 |        0,1 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+-----------+------------+-------+--------------+
|       ... |        ... | ...   | ...          |
+-----------+------------+-------+--------------+
|      3071 |      31,31 | 16,23 | LS2          |
|           |            | 08-15 | LS1          |
|           |            | 00-07 | LS0          |
+-----------+------------+-------+--------------+

The mesh_scale member determines the precision and minimum and maximum gain. For example if mesh_scale is 0 and therefore selects 0 - 2x gain, a value of 0 in a coefficient means 0.0 gain, a value of 128 means 1.0 gain and 255 means 2.0 gain.

header.type should be set to MALI_C55_PARAM_MESH_SHADING_CONFIG from mali_c55_param_block_type for this block.

struct mali_c55_params_mesh_shading_selection¶: Mesh table selection

Definition:

struct mali_c55_params_mesh_shading_selection {
    struct v4l2_isp_params_block_header header;
    __u8 mesh_alpha_bank_r;
    __u8 mesh_alpha_bank_g;
    __u8 mesh_alpha_bank_b;
    __u8 mesh_alpha_r;
    __u8 mesh_alpha_g;
    __u8 mesh_alpha_b;
    __u16 mesh_strength;
};

Members

header: The Mali-C55 parameters block header
mesh_alpha_bank_r: Red mesh table select (c:type:enum mali_c55_params_mesh_alpha_bank)
mesh_alpha_bank_g: Green mesh table select (c:type:enum mali_c55_params_mesh_alpha_bank)
mesh_alpha_bank_b: Blue mesh table select (c:type:enum mali_c55_params_mesh_alpha_bank)
mesh_alpha_r: Blend coefficient for R [0..255]
mesh_alpha_g: Blend coefficient for G [0..255]
mesh_alpha_b: Blend coefficient for B [0..255]
mesh_strength: Mesh strength in Q4.12 format [0..4096]

Description

The module computes the final correction coefficients by blending the ones from two light source tables, which are selected (independently for each colour channel) by the mesh_alpha_bank_r/g/b fields.

The final blended coefficients for each node are calculated using the following equation:

Final coefficient = (a * LS_b+ (256 - a) * LS_a) / 256

Where a is the mesh_alpha_r/g/b value, and LS_aand LS_bare the node cofficients for the two tables selected by the mesh_alpha_bank_r/g/b value.

The scale of the applied correction may also be controlled by tuning the mesh_strength member. This is a modifier to the final coefficients which can be used to globally reduce the gains applied.

header.type should be set to MALI_C55_PARAM_MESH_SHADING_SELECTION from mali_c55_param_block_type for this block.

MALI_C55_PARAMS_MAX_SIZE¶

MALI_C55_PARAMS_MAX_SIZE

Maximum size of all Mali C55 Parameters

Description

Though the parameters for the Mali-C55 are passed as optional blocks, the driver still needs to know the absolute maximum size so that it can allocate a buffer sized appropriately to accommodate userspace attempting to set all possible parameters in a single frame.

Some structs are in this list multiple times. Where that’s the case, it just reflects the fact that the same struct can be used with multiple different header types from mali_c55_param_block_type.

The Linux Kernel

Contents

This Page

2.13.1. V4L2_META_FMT_MALI_C55_STATS (‘C55S’), V4L2_META_FMT_MALI_C55_PARAMS (‘C55P’)¶

2.13.1.1. 3A Statistics¶

2.13.1.2. Configuration Parameters¶

2.13.1.3. Arm Mali-C55 uAPI data types¶