Re: [PATCH v5 09/16] media: uapi: Add 3a stats buffer for mali-c55

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Dan,

Thank you for the patch.

On Wed, May 29, 2024 at 04:28:51PM +0100, Daniel Scally wrote:
> Add a header that describes the format of the 3A statistics buffers
> for the mali-c55 ISP.
> 
> 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 v5:
> 
> 	- New patch
> 
>  .../uapi/linux/media/arm/mali-c55-config.h    | 182 ++++++++++++++++++
>  1 file changed, 182 insertions(+)
>  create mode 100644 include/uapi/linux/media/arm/mali-c55-config.h
> 
> diff --git a/include/uapi/linux/media/arm/mali-c55-config.h b/include/uapi/linux/media/arm/mali-c55-config.h
> new file mode 100644
> index 000000000000..8fb89af6c874
> --- /dev/null
> +++ b/include/uapi/linux/media/arm/mali-c55-config.h
> @@ -0,0 +1,182 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * ARM Mali-C55 ISP Driver - Userspace API
> + *
> + * Copyright (C) 2023 Ideas on Board Oy
> + */
> +
> +#ifndef __UAPI_MALI_C55_CONFIG_H
> +#define __UAPI_MALI_C55_CONFIG_H
> +
> +#include <linux/types.h>
> +
> +/*
> + * 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	225

Maybe

#define MALI_C55_MAX_ZONES	(15 * 15)

to match the comment above ? Or do you think the result of the
multiplication is more important to see at a quick glance ?

> +
> +/**
> + * 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) x 2^e

x or *, up to you, but pick one :-) Same below.

> + *	}
> + *
> + * 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 x (m + 2^9)
> + *	}
> + *
> + * where
> + *	e is the exponent value in range 0..128

If the exponent is stored on 7 bits, isn't this 0..127 ?

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> + *	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 */

-- 
Regards,

Laurent Pinchart

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