AppleJPEGDriver decode routine for the Apple M1

demo.m

/*
 * Copyright (C) 2021 Alyssa Rosenzweig <alyssa@rosenzweig.io>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include <stdio.h>
#include <assert.h>
#include <mach/mach.h>
#include <IOKit/IOKitLib.h>
#include <IOSurface/IOSurface.h>
#import <Cocoa/Cocoa.h>

@class NSNumber;

struct JPEGDriverArgs {
	IOSurfaceID src_surface /*in*/;
	unsigned int input_jpeg_file_size /*in*/; // GOOD
	IOSurfaceID dest_surface /*in*/;
	unsigned int output_buffer_size /*in*/; // GOOD
	int unk10;
	int pixel_x;
	int pixel_y;
	int unk1C;
	int unk20;
	int x_offset;
	int y_offset;
	int subsampling_mode;
	int unk30;
	int unk34;
	int unk38;
	int unk3C;
	int unk40;
	int unk44;
	int unk48;
	unsigned int decode_width;
	unsigned int decode_height;
	int unk5C;
} __attribute__((packed));

int main(int argc, char **argv)
{
	(void) argc;
	(void) argv;

	kern_return_t ret;

	CFDictionaryRef matching = IOServiceMatching("AppleJPEGDriver");

	io_service_t service =
		IOServiceGetMatchingService(kIOMasterPortDefault, matching);

	if (!service) {
		fprintf(stderr, "JPEG driver accelerator not found\n");
		return 1;
	}

	io_connect_t connection = 0;
	ret = IOServiceOpen(service, mach_task_self(), 0, &connection);

	if (ret) {
		fprintf(stderr, "Error from IOServiceOpen: %u\n", ret);
		return 1;
	}

	IOSurfaceRef surfs[2];

	char pixelFormat[4] = {'A', 'R', 'G', 'B'};
	unsigned int p = 111;
	memcpy(&p, &pixelFormat[0], 4);
	printf("%X\n", p);

	/* input jpeg */
	surfs[0] = IOSurfaceCreate((CFDictionaryRef)@{(id)kIOSurfaceWidth: @120,
			(id)kIOSurfaceHeight: @80,
			(id)kIOSurfacePixelFormat: @(p),
			(id)kIOSurfaceBytesPerElement: @4});

	/* output image */
	surfs[1] = IOSurfaceCreate((CFDictionaryRef)@{(id)kIOSurfaceWidth: @120,
			(id)kIOSurfaceHeight: @80,
			(id)kIOSurfaceBytesPerRow: @(120*4),
			(id)kIOSurfacePixelFormat: @(p),
			(id)kIOSurfaceBytesPerElement: @4});

	void *base = IOSurfaceGetBaseAddress(surfs[0]);
	FILE *fp = fopen("dump.jpg", "rb");
	fread(base, 1, 3178, fp);
	fclose(fp);

	printf("Connection %d\n", connection); 
	size_t sz = sizeof(struct JPEGDriverArgs);

	struct JPEGDriverArgs args = {
		.src_surface = IOSurfaceGetID(surfs[0]),
		.input_jpeg_file_size = 3178,
		.dest_surface = IOSurfaceGetID(surfs[1]),
		.decode_width = 120,
		.decode_height = 80,
		.pixel_x = 120,
		.pixel_y = 80,
		.output_buffer_size = 1024*1024*16,
		.x_offset = 0,
		.y_offset = 0,
	};

	ret = IOConnectCallStructMethod(connection, 1, &args,
			sizeof(args), &args, &sz);

	sleep(2);

	ret = IOServiceClose(connection);

	{
		base = IOSurfaceGetBaseAddress(surfs[1]);
		FILE *fp = fopen("dump.bin", "wb");
		fwrite(base, 1, 120*80*4, fp);
		fclose(fp);
	}

	if (ret) {
		fprintf(stderr, "Error from IOServiceClose: %u\n", ret);
		return 1;
	}
}

You should be able to pass a four-character code 'abcd' to the pixel format parameter directly; Apple uses them all over the place. See for instance CoreVideo/CVPixelBuffer.h.
The only weird thing is that your code effectively sets p to 'BGRA' (or kCVPixelFormatType_32BGRA), not ARGB. So… which pixel format actually ends up being used?

BGRA, which is what I intended. Even though the endianness makes it looks like ARGB (which is a very odd format indeed..) I am just so used to reading fourcc's backwards at this point :p

BGRA, which is what I intended. Even though the endianness makes it looks like ARGB (which is a very odd format indeed..) I am just so used to reading fourcc's backwards at this point :p

The world would be a better place with big endian systems only 🙃.
I sometimes run software tests on powerpc BE via the free unicamp minicloud, just to probe for funky memory indexing and char/numeric type casting