diff mbox series

[PATCHv2] mmc-utils: Implement alternative boot operation

Message ID 660600d1ad5949cea4fc3088a16af634@hyperstone.com (mailing list archive)
State New, archived
Headers show
Series [PATCHv2] mmc-utils: Implement alternative boot operation | expand

Commit Message

Christian Loehle Oct. 25, 2022, 8:06 p.m. UTC
Implements the alternative boot operation for eMMCs.
Note the limitations of the help.

This is mostly useful for testing purposes if you set
up the boot partition configuration correctly.

Usage:
$ sudo dd if=/dev/mmcblk2boot0 of=bootdatammcblk count=2
2+0 records in
2+0 records out
1024 bytes (1.0 kB, 1.0 KiB) copied, 0.00482308 s, 212 kB/s

$ sudo ./mmc boot_operation bootdata /dev/mmcblk2

$ diff -s bootdata bootdatammcblk
Files bootdata and bootdatammcblk are identical

Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
---
-v2: Frees, closes, removal of boot_blocks parameter and boot ack check
 mmc.c      | 12 +++++++
 mmc.h      |  3 ++
 mmc_cmds.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 mmc_cmds.h |  1 +
 4 files changed, 115 insertions(+)

Comments

Avri Altman Oct. 26, 2022, 6:47 a.m. UTC | #1
> Implements the alternative boot operation for eMMCs.
> Note the limitations of the help.
> 
> This is mostly useful for testing purposes if you set
> up the boot partition configuration correctly.
> 
> Usage:
> $ sudo dd if=/dev/mmcblk2boot0 of=bootdatammcblk count=2
> 2+0 records in
> 2+0 records out
> 1024 bytes (1.0 kB, 1.0 KiB) copied, 0.00482308 s, 212 kB/s
> 
> $ sudo ./mmc boot_operation bootdata /dev/mmcblk2
> 
> $ diff -s bootdata bootdatammcblk
> Files bootdata and bootdatammcblk are identical
> 
> Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
Few nits below.  Other than that - 
Reviewed-by: Avri Altman <avri.altman@wdc.com>

> ---
> -v2: Frees, closes, removal of boot_blocks parameter and boot ack check
>  mmc.c      | 12 +++++++
>  mmc.h      |  3 ++
>  mmc_cmds.c | 99
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  mmc_cmds.h |  1 +
>  4 files changed, 115 insertions(+)
> 
> diff --git a/mmc.c b/mmc.c
> index 170ee39..adcd814 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> <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. Only up to 512K bytes of boot data will be transferred.\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",
Theoretically, this shouldn't happen unless you send additional cmd0/0x0.
But I guess it's a reasonable decision for the device to make if it doesn't get one, or cmd1.

> +         NULL
> +       },
>         { 0, 0, 0, 0 }
>  };
> 
> diff --git a/mmc.h b/mmc.h
> index 6511dbc..4de0aae 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  */
> @@ -97,6 +98,7 @@
>  #define EXT_CSD_CACHE_SIZE_0           249
>  #define EXT_CSD_SEC_FEATURE_SUPPORT    231
>  #define EXT_CSD_BOOT_INFO              228     /* R/W */
> +#define EXT_CSD_BOOT_MULT              226     /* RO */
>  #define EXT_CSD_HC_ERASE_GRP_SIZE      224
>  #define EXT_CSD_HC_WP_GRP_SIZE         221
>  #define EXT_CSD_SEC_COUNT_3            215
> @@ -107,6 +109,7 @@
>  #define EXT_CSD_REV                    192
>  #define EXT_CSD_BOOT_CFG               179
>  #define EXT_CSD_PART_CONFIG            179
> +#define EXT_CSD_PART_CONFIG_BOOT_ACK   (1 << 6)
Already exist - EXT_CSD_PART_CONFIG_ACC_ACK

>  #define EXT_CSD_BOOT_BUS_CONDITIONS    177
>  #define EXT_CSD_ERASE_GROUP_DEF                175
>  #define EXT_CSD_BOOT_WP_STATUS         174
> diff --git a/mmc_cmds.c b/mmc_cmds.c
> index 3db17e1..b7efe5a 100644
> --- a/mmc_cmds.c
> +++ b/mmc_cmds.c
> @@ -3101,3 +3101,102 @@ 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 != 3) {
> +               fprintf(stderr, "Usage: mmc boot_op <boot_data_file>
> </path/to/mmcblkX>\n");
> +               exit(1);
> +       }
> +       boot_data_file = argv[1];
> +       device = argv[2];
> +
> +       fd = open(device, O_RDWR);
> +       if (fd < 0) {
> +               perror("open device");
> +               exit(1);
> +       }
> +
> +       ret = read_extcsd(fd, ext_csd);
> +       if (ret) {
> +               perror("read extcsd");
> +               goto dev_fd_close;
> +       }
> +       if ((ext_csd[EXT_CSD_PART_CONFIG] &
> EXT_CSD_PART_CONFIG_BOOT_ACK)
> +                       == EXT_CSD_PART_CONFIG_BOOT_ACK) {
Redundant rhs?

> +               perror("Boot Ack must not be enabled");
> +               ret = -EINVAL;
> +               goto dev_fd_close;
> +       }
> +       ext_csd_boot_size = ext_csd[EXT_CSD_BOOT_MULT] * 128 * 1024;
> +       boot_blocks = ext_csd_boot_size / 512;
> +       if (ext_csd_boot_size > MMC_IOC_MAX_BYTES) {
> +               printf("Boot partition size is bigger than IOCTL limit, limiting to
> 512K\n");
> +               boot_blocks = MMC_IOC_MAX_BYTES / 512;
> +       }
> +
> +       boot_data_fd = open(boot_data_file, O_WRONLY | O_CREAT, 0644);
> +       if (boot_data_fd < 0) {
> +               perror("open boot data file");
> +               ret = 1;
> +               goto boot_data_close;
> +       }
> +
> +       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");
> +               ret = -ENOMEM;
> +               goto alloced_error;
> +       }
> +
> +       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\n");
> +               goto alloced_error;
> +       }
> +
> +       ret = DO_IO(write, boot_data_fd, boot_buf, boot_blocks * 512);
> +       if (ret < 0) {
> +               perror("Write error\n");
> +               goto alloced_error;
> +       }
> +       ret = 0;
> +
> +alloced_error:
> +       if (mioc)
> +               free(mioc);
> +       if (boot_buf)
> +               free(boot_buf);
> +boot_data_close:
> +       close(boot_data_fd);
> +dev_fd_close:
> +       close(fd);
> +       if (ret)
> +               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);
> --
> 2.37.3
> 
> Hyperstone GmbH | Reichenaustr. 39a  | 78467 Konstanz
> Managing Director: Dr. Jan Peter Berns.
> Commercial register of local courts: Freiburg HRB381782
Avri Altman Oct. 26, 2022, 7:01 a.m. UTC | #2
> > Implements the alternative boot operation for eMMCs.
> > Note the limitations of the help.
> >
> > This is mostly useful for testing purposes if you set up the boot
> > partition configuration correctly.
> >
> > Usage:
> > $ sudo dd if=/dev/mmcblk2boot0 of=bootdatammcblk count=2
> > 2+0 records in
> > 2+0 records out
> > 1024 bytes (1.0 kB, 1.0 KiB) copied, 0.00482308 s, 212 kB/s
> >
> > $ sudo ./mmc boot_operation bootdata /dev/mmcblk2
> >
> > $ diff -s bootdata bootdatammcblk
> > Files bootdata and bootdatammcblk are identical
> >
> > Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
> Few nits below.  Other than that -
Sorry - you also forgot to add the check of alternative boot support:
(ext_csd[EXT_CSD_BOOT_INFO] & EXT_CSD_BOOT_INFO_ALT)

Please do.

Thanks,
Avri
> Reviewed-by: Avri Altman <avri.altman@wdc.com>
> 
> > ---
> > -v2: Frees, closes, removal of boot_blocks parameter and boot ack check
> >  mmc.c      | 12 +++++++
> >  mmc.h      |  3 ++
> >  mmc_cmds.c | 99
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  mmc_cmds.h |  1 +
> >  4 files changed, 115 insertions(+)
> >
> > diff --git a/mmc.c b/mmc.c
> > index 170ee39..adcd814 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> <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. Only up to 512K bytes of boot data will be transferred.\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",
> Theoretically, this shouldn't happen unless you send additional cmd0/0x0.
> But I guess it's a reasonable decision for the device to make if it doesn't get
> one, or cmd1.
> 
> > +         NULL
> > +       },
> >         { 0, 0, 0, 0 }
> >  };
> >
> > diff --git a/mmc.h b/mmc.h
> > index 6511dbc..4de0aae 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  */
> > @@ -97,6 +98,7 @@
> >  #define EXT_CSD_CACHE_SIZE_0           249
> >  #define EXT_CSD_SEC_FEATURE_SUPPORT    231
> >  #define EXT_CSD_BOOT_INFO              228     /* R/W */
> > +#define EXT_CSD_BOOT_MULT              226     /* RO */
> >  #define EXT_CSD_HC_ERASE_GRP_SIZE      224
> >  #define EXT_CSD_HC_WP_GRP_SIZE         221
> >  #define EXT_CSD_SEC_COUNT_3            215
> > @@ -107,6 +109,7 @@
> >  #define EXT_CSD_REV                    192
> >  #define EXT_CSD_BOOT_CFG               179
> >  #define EXT_CSD_PART_CONFIG            179
> > +#define EXT_CSD_PART_CONFIG_BOOT_ACK   (1 << 6)
> Already exist - EXT_CSD_PART_CONFIG_ACC_ACK
> 
> >  #define EXT_CSD_BOOT_BUS_CONDITIONS    177
> >  #define EXT_CSD_ERASE_GROUP_DEF                175
> >  #define EXT_CSD_BOOT_WP_STATUS         174
> > diff --git a/mmc_cmds.c b/mmc_cmds.c
> > index 3db17e1..b7efe5a 100644
> > --- a/mmc_cmds.c
> > +++ b/mmc_cmds.c
> > @@ -3101,3 +3101,102 @@ 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 != 3) {
> > +               fprintf(stderr, "Usage: mmc boot_op <boot_data_file>
> > </path/to/mmcblkX>\n");
> > +               exit(1);
> > +       }
> > +       boot_data_file = argv[1];
> > +       device = argv[2];
> > +
> > +       fd = open(device, O_RDWR);
> > +       if (fd < 0) {
> > +               perror("open device");
> > +               exit(1);
> > +       }
> > +
> > +       ret = read_extcsd(fd, ext_csd);
> > +       if (ret) {
> > +               perror("read extcsd");
> > +               goto dev_fd_close;
> > +       }
> > +       if ((ext_csd[EXT_CSD_PART_CONFIG] &
> > EXT_CSD_PART_CONFIG_BOOT_ACK)
> > +                       == EXT_CSD_PART_CONFIG_BOOT_ACK) {
> Redundant rhs?
> 
> > +               perror("Boot Ack must not be enabled");
> > +               ret = -EINVAL;
> > +               goto dev_fd_close;
> > +       }
> > +       ext_csd_boot_size = ext_csd[EXT_CSD_BOOT_MULT] * 128 * 1024;
> > +       boot_blocks = ext_csd_boot_size / 512;
> > +       if (ext_csd_boot_size > MMC_IOC_MAX_BYTES) {
> > +               printf("Boot partition size is bigger than IOCTL
> > + limit, limiting to
> > 512K\n");
> > +               boot_blocks = MMC_IOC_MAX_BYTES / 512;
> > +       }
> > +
> > +       boot_data_fd = open(boot_data_file, O_WRONLY | O_CREAT, 0644);
> > +       if (boot_data_fd < 0) {
> > +               perror("open boot data file");
> > +               ret = 1;
> > +               goto boot_data_close;
> > +       }
> > +
> > +       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");
> > +               ret = -ENOMEM;
> > +               goto alloced_error;
> > +       }
> > +
> > +       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\n");
> > +               goto alloced_error;
> > +       }
> > +
> > +       ret = DO_IO(write, boot_data_fd, boot_buf, boot_blocks * 512);
> > +       if (ret < 0) {
> > +               perror("Write error\n");
> > +               goto alloced_error;
> > +       }
> > +       ret = 0;
> > +
> > +alloced_error:
> > +       if (mioc)
> > +               free(mioc);
> > +       if (boot_buf)
> > +               free(boot_buf);
> > +boot_data_close:
> > +       close(boot_data_fd);
> > +dev_fd_close:
> > +       close(fd);
> > +       if (ret)
> > +               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);
> > --
> > 2.37.3
> >
> > Hyperstone GmbH | Reichenaustr. 39a  | 78467 Konstanz Managing
> > Director: Dr. Jan Peter Berns.
> > Commercial register of local courts: Freiburg HRB381782
diff mbox series

Patch

diff --git a/mmc.c b/mmc.c
index 170ee39..adcd814 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> <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. Only up to 512K bytes of boot data will be transferred.\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..4de0aae 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  */
@@ -97,6 +98,7 @@ 
 #define EXT_CSD_CACHE_SIZE_0		249
 #define EXT_CSD_SEC_FEATURE_SUPPORT	231
 #define EXT_CSD_BOOT_INFO		228	/* R/W */
+#define EXT_CSD_BOOT_MULT		226	/* RO */
 #define EXT_CSD_HC_ERASE_GRP_SIZE	224
 #define EXT_CSD_HC_WP_GRP_SIZE		221
 #define EXT_CSD_SEC_COUNT_3		215
@@ -107,6 +109,7 @@ 
 #define EXT_CSD_REV			192
 #define EXT_CSD_BOOT_CFG		179
 #define EXT_CSD_PART_CONFIG		179
+#define EXT_CSD_PART_CONFIG_BOOT_ACK	(1 << 6)
 #define EXT_CSD_BOOT_BUS_CONDITIONS	177
 #define EXT_CSD_ERASE_GROUP_DEF		175
 #define EXT_CSD_BOOT_WP_STATUS		174
diff --git a/mmc_cmds.c b/mmc_cmds.c
index 3db17e1..b7efe5a 100644
--- a/mmc_cmds.c
+++ b/mmc_cmds.c
@@ -3101,3 +3101,102 @@  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 != 3) {
+		fprintf(stderr, "Usage: mmc boot_op <boot_data_file> </path/to/mmcblkX>\n");
+		exit(1);
+	}
+	boot_data_file = argv[1];
+	device = argv[2];
+
+	fd = open(device, O_RDWR);
+	if (fd < 0) {
+		perror("open device");
+		exit(1);
+	}
+
+	ret = read_extcsd(fd, ext_csd);
+	if (ret) {
+		perror("read extcsd");
+		goto dev_fd_close;
+	}
+	if ((ext_csd[EXT_CSD_PART_CONFIG] & EXT_CSD_PART_CONFIG_BOOT_ACK)
+			== EXT_CSD_PART_CONFIG_BOOT_ACK) {
+		perror("Boot Ack must not be enabled");
+		ret = -EINVAL;
+		goto dev_fd_close;
+	}
+	ext_csd_boot_size = ext_csd[EXT_CSD_BOOT_MULT] * 128 * 1024;
+	boot_blocks = ext_csd_boot_size / 512;
+	if (ext_csd_boot_size > MMC_IOC_MAX_BYTES) {
+		printf("Boot partition size is bigger than IOCTL limit, limiting to 512K\n");
+		boot_blocks = MMC_IOC_MAX_BYTES / 512;
+	}
+
+	boot_data_fd = open(boot_data_file, O_WRONLY | O_CREAT, 0644);
+	if (boot_data_fd < 0) {
+		perror("open boot data file");
+		ret = 1;
+		goto boot_data_close;
+	}
+
+	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");
+		ret = -ENOMEM;
+		goto alloced_error;
+	}
+
+	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\n");
+		goto alloced_error;
+	}
+
+	ret = DO_IO(write, boot_data_fd, boot_buf, boot_blocks * 512);
+	if (ret < 0) {
+		perror("Write error\n");
+		goto alloced_error;
+	}
+	ret = 0;
+
+alloced_error:
+	if (mioc)
+		free(mioc);
+	if (boot_buf)
+		free(boot_buf);
+boot_data_close:
+	close(boot_data_fd);
+dev_fd_close:
+	close(fd);
+	if (ret)
+		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);