[PATCH v10 11/17] media: uapi: Add 3a stats buffer for mali-c55

Daniel Scally
2025-06-24T10:21:54Z

Describe the format of the 3A statistics buffers in the userspace API
header for the mali-c55 ISP.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Nayden Kanchev <nayden.kanchev@arm.com>
Co-developed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
---
Changes in v10:

- None

Changes in v9:

- None

Changes in v8:

- None

Changes in v7:

- None

Changes in v6:

- New patch

Changes in v5:

- New patch
---
MAINTAINERS | 1 +
include/uapi/linux/media/arm/mali-c55-config.h | 170 +++++++++++++++++++++++++
2 files changed, 171 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 43204b809333bf8f3d05a65fb3c24b063c91c2a4..af4dce215fd3bd22de09c41c9469c3bf69609bd7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2039,6 +2039,7 @@ F: Documentation/admin-guide/media/mali-c55.rst
F: Documentation/devicetree/bindings/media/arm,mali-c55.yaml
F: Documentation/userspace-api/media/drivers/mali-c55.rst
F: drivers/media/platform/arm/mali-c55/
+F: include/uapi/linux/media/arm/mali-c55-config.h

ARM MALI PANTHOR DRM DRIVER
M: Boris Brezillon <boris.brezillon@collabora.com>
diff --git a/include/uapi/linux/media/arm/mali-c55-config.h b/include/uapi/linux/media/arm/mali-c55-config.h
index 2bd60a0d78786be368c2e51b1a0a63fd2a5f690b..8d31764140a0ef6aa8b0c771a4ed7565c9c96670 100644
--- a/include/uapi/linux/media/arm/mali-c55-config.h
+++ b/include/uapi/linux/media/arm/mali-c55-config.h
@@ -8,6 +8,7 @@
#ifndef __UAPI_MALI_C55_CONFIG_H
#define __UAPI_MALI_C55_CONFIG_H

+#include <linux/types.h>
#include <linux/v4l2-controls.h>

#define V4L2_CID_MALI_C55_CAPABILITIES (V4L2_CID_USER_MALI_C55_BASE + 0x0)
@@ -23,4 +24,173 @@
#define MALI_C55_GPS_FRSCALER_FITTED BIT(9)
#define MALI_C55_GPS_DS_PIPE_FITTED BIT(10)

+/*
+ * Frames are split into zones of almost equal width and height - a zone is a
+ * rectangular tile of a frame. The metering blocks within the ISP collect
+ * aggregated statistics per zone. A maximum of 15x15 zones can be configured,
+ * and so the statistics buffer within the hardware is sized to accommodate
+ * that.
+ *
+ * The utilised number of zones is runtime configurable.
+ */
+#define MALI_C55_MAX_ZONES (15 * 15)
+
+/**
+ * struct mali_c55_ae_1024bin_hist - Auto Exposure 1024-bin histogram statistics
+ *
+ * @bins: 1024 element array of 16-bit pixel counts.
+ *
+ * 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:
+ *
+ * 1. Pixels can be skipped in X and Y directions independently.
+ * 2. Minimum/Maximum intensities can be configured
+ * 3. 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_1024bin_hist {
+ __u16 bins[1024];
+} __attribute__((packed));
+
+/**
+ * struct mali_c55_ae_5bin_hist - Auto Exposure 5-bin histogram statistics
+ *
+ * @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
+ *
+ * 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_ae_5bin_hist {
+ __u16 hist0;
+ __u16 hist1;
+ __u16 hist3;
+ __u16 hist4;
+} __attribute__((packed));
+
+/**
+ * struct mali_c55_awb_average_ratios - Auto White Balance colour ratios
+ *
+ * @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
+ *
+ * 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_awb_average_ratios {
+ __u16 avg_rg_gr;
+ __u16 avg_bg_br;
+ __u32 num_pixels;
+} __attribute__((packed));
+
+/**
+ * struct mali_c55_af_statistics - Auto Focus edge and intensity statistics
+ *
+ * @intensity_stats: Packed mantissa and exponent value for pixel intensity
+ * @edge_stats: Packed mantissa and exponent values for edge intensity
+ *
+ * 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_af_statistics {
+ __u16 intensity_stats;
+ __u16 edge_stats;
+} __attribute__((packed));
+
+/**
+ * struct mali_c55_stats_buffer - 3A statistics for the mali-c55 ISP
+ *
+ * @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
+ *
+ * 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.
+ */
+
+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];
+} __attribute__((packed));
+
#endif /* __UAPI_MALI_C55_CONFIG_H */

--
2.34.1