mmc-utils: Implement alternative boot operation

diff --git a/mmc.c b/mmc.c
index 170ee39..f328585 100644
--- a/mmc.c
+++ b/mmc.c
@@ -255,6 +255,18 @@  static struct Command commands[] = {
 	  "Issues a CMD0 GO_PRE_IDLE",
 	  NULL
 	},
+	{ do_alt_boot_op, -1,
+	  "boot_operation", "<boot_data_file> <boot_blocks> <device>\n"
+	  "Does the alternative boot operation and writes the specified starting blocks of boot data into the requested file.\n\n"
+	  "Note some limitations\n:"
+	  "1. The boot operation must be configured, e.g. for legacy speed:\n"
+	  "mmc-utils bootbus set single_backward retain x8 /dev/mmcblk2\n"
+	  "mmc-utils bootpart enable 1 0 /dev/mmcblk2\n"
+	  "2. The MMC must currently be running at the bus mode that is configured for the boot operation (HS200 and HS400 not supported at all).\n"
+	  "3. Most hosts cannot do transfers of the typical size of the boot partition, adjust <boot_blocks> accordingly.\n"
+	  "4. The MMC will perform a soft reset, if your system cannot handle that do not use the boot operation from mmc-utils.\n",
+	  NULL
+	},
 	{ 0, 0, 0, 0 }
 };
 
diff --git a/mmc.h b/mmc.h
index 6511dbc..98fad16 100644
--- a/mmc.h
+++ b/mmc.h
@@ -24,6 +24,7 @@ 
 #define MMC_GO_IDLE_STATE         0   /* bc                          */
 #define MMC_GO_IDLE_STATE_ARG		0x0
 #define MMC_GO_PRE_IDLE_STATE_ARG	0xF0F0F0F0
+#define MMC_BOOT_INITIATION_ARG		0xFFFFFFFA
 #define MMC_SWITCH		6	/* ac	[31:0] See below	R1b */
 #define MMC_SEND_EXT_CSD	8	/* adtc				R1  */
 #define MMC_SEND_STATUS		13	/* ac   [31:16] RCA        R1  */
diff --git a/mmc_cmds.c b/mmc_cmds.c
index 3db17e1..1da61d4 100644
--- a/mmc_cmds.c
+++ b/mmc_cmds.c
@@ -3101,3 +3101,79 @@  int do_preidle(int nargs, char **argv)
 
 	return 0;
 }
+
+int do_alt_boot_op(int nargs, char **argv)
+{
+	int fd, ret, boot_data_fd;
+	char *device, *boot_data_file;
+	struct mmc_ioc_multi_cmd *mioc;
+	__u8 ext_csd[512];
+	__u8 *boot_buf;
+	unsigned int boot_blocks, ext_csd_boot_size;
+
+	if (nargs != 4) {
+		fprintf(stderr, "Usage: mmc boot_op <boot_data_file> <boot_blocks> </path/to/mmcblkX>\n");
+		exit(1);
+	}
+	boot_data_file = argv[1];
+	boot_blocks = strtol(argv[2], NULL, 10);
+	device = argv[3];
+
+	fd = open(device, O_RDWR);
+	if (fd < 0) {
+		perror("open device");
+		exit(1);
+	}
+	boot_data_fd = open(boot_data_file, O_WRONLY | O_CREAT, 0644);
+	if (boot_data_fd < 0) {
+		perror("open boot data file");
+		exit(1);
+	}
+
+	ret = read_extcsd(fd, ext_csd);
+	if (ret) {
+		perror("read extcsd");
+		exit(1);
+	}
+	ext_csd_boot_size = ext_csd[226] * 128 * 1024;
+	if (boot_blocks * 512 > ext_csd_boot_size) {
+		perror("Requested boot size bigger than boot partition");
+		exit(1);
+	}
+
+	boot_buf = calloc(1, sizeof(__u8) * boot_blocks * 512);
+	mioc = calloc(1, sizeof(struct mmc_ioc_multi_cmd) +
+			   2 * sizeof(struct mmc_ioc_cmd));
+	if (!mioc || !boot_buf) {
+		perror("Failed to allocate memory");
+		return -ENOMEM;
+	}
+
+	mioc->num_of_cmds = 2;
+	mioc->cmds[0].opcode = MMC_GO_IDLE_STATE;
+	mioc->cmds[0].arg = MMC_GO_PRE_IDLE_STATE_ARG;
+	mioc->cmds[0].flags = MMC_RSP_NONE | MMC_CMD_AC;
+	mioc->cmds[0].write_flag = 0;
+
+	mioc->cmds[1].opcode = MMC_GO_IDLE_STATE;
+	mioc->cmds[1].arg = MMC_BOOT_INITIATION_ARG;
+	mioc->cmds[1].flags = MMC_RSP_NONE | MMC_CMD_ADTC;
+	mioc->cmds[1].write_flag = 0;
+	mioc->cmds[1].blksz = 512;
+	mioc->cmds[1].blocks = boot_blocks;
+	/* Access time of boot part differs wildly, spec mandates 1s */
+	mioc->cmds[1].data_timeout_ns = 2 * 1000 * 1000 * 1000;
+	mmc_ioc_cmd_set_data(mioc->cmds[1], boot_buf);
+
+	ret = ioctl(fd, MMC_IOC_MULTI_CMD, mioc);
+	if (ret)
+		perror("multi-cmd ioctl error %d\n", ret);
+	close(fd);
+
+	ret = DO_IO(write, boot_data_fd, boot_buf, boot_blocks * 512);
+	if (ret < 0) {
+		perror("Write error\n");
+		exit(1);
+	}
+	return 0;
+}
diff --git a/mmc_cmds.h b/mmc_cmds.h
index faab362..5f2bef1 100644
--- a/mmc_cmds.h
+++ b/mmc_cmds.h
@@ -49,3 +49,4 @@  int do_erase(int nargs, char **argv);
 int do_general_cmd_read(int nargs, char **argv);
 int do_softreset(int nargs, char **argv);
 int do_preidle(int nargs, char **argv);
+int do_alt_boot_op(int nargs, char **argv);