[PATCH 0/2] fastboot: block: Add GPT/MBR and device selection

[PATCH 0/2] fastboot: block: Add GPT/MBR and device selection

[Balaji Selvanathan]

This series enables GPT and MBR partition table operations for
fastboot block devices and introduces device selection syntax.

Patch 1 implements "N:partition" format to target specific block
devices (e.g., "fastboot flash 0:gpt gpt.img") and adds helper
functions to improve code maintainability.

Patch 2 documents the new syntax with usage examples.

Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
---
Balaji Selvanathan (2):
      fastboot: block: Add GPT/MBR support and device selection syntax
      doc: fastboot: Document block device selection syntax

 doc/android/fastboot.rst    |  41 +++++++++
 drivers/fastboot/Kconfig    |   4 +-
 drivers/fastboot/fb_block.c | 196 +++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 227 insertions(+), 14 deletions(-)
---
base-commit: e2fa3e570f83ab0f9ce667ddaec9dc738bcf05b9
change-id: 20260410-fb_block-14f90c7d6b37

Best regards,
-- 
Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>

[PATCH 1/2] fastboot: block: Add GPT/MBR support and device selection syntax

[Balaji Selvanathan]

Implement device selection syntax allowing users to specify the
target block device using "N:partition" format, where N is the
device number. This enables operations like "fastboot flash 0:gpt"
to write partition tables to specific devices. When no device is
specified, the default from CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID
is used.

Example usage for partition flashing:
  fastboot flash 0:boot boot.img      # Flash to device 0
  fastboot flash 1:system system.img  # Flash to device 1
  fastboot flash boot boot.img        # Use default device

Example usage for GPT/MBR operations:
  fastboot flash 0:gpt gpt.img        # Write GPT to device 0
  fastboot flash 1:mbr mbr.img        # Write MBR to device 1

Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
---
 drivers/fastboot/Kconfig    |   4 +-
 drivers/fastboot/fb_block.c | 196 +++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 186 insertions(+), 14 deletions(-)

diff --git a/drivers/fastboot/Kconfig b/drivers/fastboot/Kconfig
index 576c3ef8a45..43d83265df4 100644
--- a/drivers/fastboot/Kconfig
+++ b/drivers/fastboot/Kconfig
@@ -227,7 +227,7 @@ config FASTBOOT_FLASH_BLOCK_DEVICE_ID
 
 config FASTBOOT_GPT_NAME
 	string "Target name for updating GPT"
-	depends on FASTBOOT_FLASH_MMC && EFI_PARTITION
+	depends on (FASTBOOT_FLASH_MMC || FASTBOOT_FLASH_BLOCK) && EFI_PARTITION
 	default "gpt"
 	help
 	  The fastboot "flash" command supports writing the downloaded
@@ -240,7 +240,7 @@ config FASTBOOT_GPT_NAME
 
 config FASTBOOT_MBR_NAME
 	string "Target name for updating MBR"
-	depends on FASTBOOT_FLASH_MMC && DOS_PARTITION
+	depends on (FASTBOOT_FLASH_MMC || FASTBOOT_FLASH_BLOCK) && DOS_PARTITION
 	default "mbr"
 	help
 	  The fastboot "flash" command allows to write the downloaded image
diff --git a/drivers/fastboot/fb_block.c b/drivers/fastboot/fb_block.c
index 51d1abb18c7..c2c3a285d77 100644
--- a/drivers/fastboot/fb_block.c
+++ b/drivers/fastboot/fb_block.c
@@ -11,6 +11,7 @@
 #include <image-sparse.h>
 #include <malloc.h>
 #include <part.h>
+#include <vsprintf.h>
 
 /**
  * FASTBOOT_MAX_BLOCKS_ERASE - maximum blocks to erase per derase call
@@ -124,6 +125,79 @@ static lbaint_t fb_block_sparse_reserve(struct sparse_storage *info,
 	return blkcnt;
 }
 
+/**
+ * parse_device_partition() - Parse device:partition format
+ * @part_name: Input string in format "N:partition" or "partition"
+ * @device: Output device number
+ * @partition_name: Output partition name pointer
+ *
+ * Parses the input string to extract device number and partition name.
+ * If no device is specified, uses the default from config.
+ */
+static void parse_device_partition(const char *part_name, int *device,
+				   const char **partition_name)
+{
+	const char *colon_pos;
+
+	/* Default: no device specified, use config default */
+	*device = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
+				     CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID, -1);
+	*partition_name = part_name;
+
+	/* Override if device:partition format detected */
+	colon_pos = strchr(part_name, ':');
+	if (colon_pos && colon_pos > part_name) {
+		*device = simple_strtoul(part_name, NULL, 10);
+		*partition_name = colon_pos + 1;
+	}
+}
+
+/**
+ * get_block_device() - Get block device descriptor
+ * @interface: Block interface name (e.g., "mmc", "scsi")
+ * @device: Device number
+ * @response: Fastboot response buffer
+ *
+ * Returns: Block device descriptor or NULL on error
+ */
+static struct blk_desc *get_block_device(const char *interface, int device,
+					 char *response)
+{
+	struct blk_desc *dev_desc;
+
+	if (!interface || !strcmp(interface, "")) {
+		fastboot_fail("block interface isn't provided", response);
+		return NULL;
+	}
+
+	dev_desc = blk_get_dev(interface, device);
+	if (!dev_desc)
+		fastboot_fail("no such device", response);
+
+	return dev_desc;
+}
+
+/**
+ * is_partition_table_name() - Check if name matches partition table target
+ * @part_name: Partition name to check
+ * @table_name: Config name for partition table (e.g., "gpt", "mbr")
+ *
+ * Returns: true if part_name matches table_name (with or without device prefix)
+ */
+static bool is_partition_table_name(const char *part_name, const char *table_name)
+{
+	const char *colon_pos;
+
+	if (strcmp(part_name, table_name) == 0)
+		return true;
+
+	colon_pos = strchr(part_name, ':');
+	if (colon_pos && strcmp(colon_pos + 1, table_name) == 0)
+		return true;
+
+	return false;
+}
+
 int fastboot_block_get_part_info(const char *part_name,
 				 struct blk_desc **dev_desc,
 				 struct disk_partition *part_info,
@@ -133,25 +207,21 @@ int fastboot_block_get_part_info(const char *part_name,
 	const char *interface = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
 						   CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
 						   NULL);
-	const int device = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
-					      CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID, -1);
+	int device;
+	const char *partition_name;
 
 	if (!part_name || !strcmp(part_name, "")) {
 		fastboot_fail("partition not given", response);
 		return -ENOENT;
 	}
-	if (!interface || !strcmp(interface, "")) {
-		fastboot_fail("block interface isn't provided", response);
-		return -EINVAL;
-	}
 
-	*dev_desc = blk_get_dev(interface, device);
-	if (!dev_desc) {
-		fastboot_fail("no such device", response);
+	parse_device_partition(part_name, &device, &partition_name);
+
+	*dev_desc = get_block_device(interface, device, response);
+	if (!*dev_desc)
 		return -ENODEV;
-	}
 
-	ret = part_get_info_by_name(*dev_desc, part_name, part_info);
+	ret = part_get_info_by_name(*dev_desc, partition_name, part_info);
 	if (ret < 0)
 		fastboot_fail("failed to get partition info", response);
 
@@ -310,12 +380,114 @@ void fastboot_block_write_sparse_image(struct blk_desc *dev_desc, struct disk_pa
 		fastboot_okay(NULL, response);
 }
 
+#if CONFIG_IS_ENABLED(EFI_PARTITION)
+/**
+ * flash_gpt_partition_table() - Flash GPT partition table
+ * @part_name: Partition name (format: "gpt" or "N:gpt")
+ * @download_buffer: Buffer containing GPT data
+ * @response: Fastboot response buffer
+ */
+static void flash_gpt_partition_table(const char *part_name, void *download_buffer,
+				      char *response)
+{
+	const char *interface = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
+						   CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
+						   NULL);
+	struct blk_desc *dev_desc;
+	int device;
+	const char *partition_name;
+
+	parse_device_partition(part_name, &device, &partition_name);
+
+	dev_desc = get_block_device(interface, device, response);
+	if (!dev_desc)
+		return;
+
+	printf("%s: updating MBR, Primary and Backup GPT(s) on %s device %d\n",
+	       __func__, interface, dev_desc->devnum);
+
+	if (is_valid_gpt_buf(dev_desc, download_buffer)) {
+		printf("%s: invalid GPT - refusing to write to flash\n", __func__);
+		fastboot_fail("invalid GPT partition", response);
+		return;
+	}
+
+	if (write_mbr_and_gpt_partitions(dev_desc, download_buffer)) {
+		printf("%s: writing GPT partitions failed\n", __func__);
+		fastboot_fail("writing GPT partitions failed", response);
+		return;
+	}
+
+	part_init(dev_desc);
+	printf("........ success\n");
+	fastboot_okay(NULL, response);
+}
+#endif
+
+#if CONFIG_IS_ENABLED(DOS_PARTITION)
+/**
+ * flash_mbr_partition_table() - Flash MBR partition table
+ * @part_name: Partition name (format: "mbr" or "N:mbr")
+ * @download_buffer: Buffer containing MBR data
+ * @response: Fastboot response buffer
+ */
+static void flash_mbr_partition_table(const char *part_name, void *download_buffer,
+				      char *response)
+{
+	const char *interface = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
+						   CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
+						   NULL);
+	struct blk_desc *dev_desc;
+	int device;
+	const char *partition_name;
+
+	parse_device_partition(part_name, &device, &partition_name);
+
+	dev_desc = get_block_device(interface, device, response);
+	if (!dev_desc)
+		return;
+
+	printf("%s: updating MBR on %s device %d\n", __func__, interface,
+	       dev_desc->devnum);
+
+	if (is_valid_dos_buf(download_buffer)) {
+		printf("%s: invalid MBR - refusing to write to flash\n", __func__);
+		fastboot_fail("invalid MBR partition", response);
+		return;
+	}
+
+	if (write_mbr_sector(dev_desc, download_buffer)) {
+		printf("%s: writing MBR partition failed\n", __func__);
+		fastboot_fail("writing MBR partition failed", response);
+		return;
+	}
+
+	part_init(dev_desc);
+	printf("........ success\n");
+	fastboot_okay(NULL, response);
+}
+#endif
+
 void fastboot_block_flash_write(const char *part_name, void *download_buffer,
 				u32 download_bytes, char *response)
 {
 	struct blk_desc *dev_desc;
 	struct disk_partition part_info;
 
+#if CONFIG_IS_ENABLED(EFI_PARTITION)
+	if (is_partition_table_name(part_name, CONFIG_FASTBOOT_GPT_NAME)) {
+		flash_gpt_partition_table(part_name, download_buffer, response);
+		return;
+	}
+#endif
+
+#if CONFIG_IS_ENABLED(DOS_PARTITION)
+	if (is_partition_table_name(part_name, CONFIG_FASTBOOT_MBR_NAME)) {
+		flash_mbr_partition_table(part_name, download_buffer, response);
+		return;
+	}
+#endif
+
 	if (fastboot_block_get_part_info(part_name, &dev_desc, &part_info, response) < 0)
 		return;
 
@@ -326,4 +498,4 @@ void fastboot_block_flash_write(const char *part_name, void *download_buffer,
 		fastboot_block_write_raw_image(dev_desc, &part_info, part_name,
 					       download_buffer, download_bytes, response);
 	}
-}
+}
\ No newline at end of file

-- 
2.34.1

Re: [PATCH 1/2] fastboot: block: Add GPT/MBR support and device selection syntax

[Mattijs Korpershoek]

Hi Balaji,

Thank you for the patch.

On Fri, Apr 10, 2026 at 10:12, Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com> wrote:

> Implement device selection syntax allowing users to specify the
> target block device using "N:partition" format, where N is the
> device number. This enables operations like "fastboot flash 0:gpt"
> to write partition tables to specific devices. When no device is
> specified, the default from CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID
> is used.

This commit is doing 2 things: Adding device selection syntax and
GPT/MBR flashing support

Can we please split this in 2 distinct patches ? device selection in a
first patch , and the GPT/MBR partition table flashing support in a second patch ?

This makes things easier to review.

>
> Example usage for partition flashing:
>   fastboot flash 0:boot boot.img      # Flash to device 0
>   fastboot flash 1:system system.img  # Flash to device 1
>   fastboot flash boot boot.img        # Use default device
>
> Example usage for GPT/MBR operations:
>   fastboot flash 0:gpt gpt.img        # Write GPT to device 0
>   fastboot flash 1:mbr mbr.img        # Write MBR to device 1
>
> Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
> ---
>  drivers/fastboot/Kconfig    |   4 +-
>  drivers/fastboot/fb_block.c | 196 +++++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 186 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/fastboot/Kconfig b/drivers/fastboot/Kconfig
> index 576c3ef8a45..43d83265df4 100644
> --- a/drivers/fastboot/Kconfig
> +++ b/drivers/fastboot/Kconfig
> @@ -227,7 +227,7 @@ config FASTBOOT_FLASH_BLOCK_DEVICE_ID
>  
>  config FASTBOOT_GPT_NAME
>  	string "Target name for updating GPT"
> -	depends on FASTBOOT_FLASH_MMC && EFI_PARTITION
> +	depends on (FASTBOOT_FLASH_MMC || FASTBOOT_FLASH_BLOCK) && EFI_PARTITION
>  	default "gpt"
>  	help
>  	  The fastboot "flash" command supports writing the downloaded
> @@ -240,7 +240,7 @@ config FASTBOOT_GPT_NAME
>  
>  config FASTBOOT_MBR_NAME
>  	string "Target name for updating MBR"
> -	depends on FASTBOOT_FLASH_MMC && DOS_PARTITION
> +	depends on (FASTBOOT_FLASH_MMC || FASTBOOT_FLASH_BLOCK) && DOS_PARTITION
>  	default "mbr"
>  	help
>  	  The fastboot "flash" command allows to write the downloaded image
> diff --git a/drivers/fastboot/fb_block.c b/drivers/fastboot/fb_block.c
> index 51d1abb18c7..c2c3a285d77 100644
> --- a/drivers/fastboot/fb_block.c
> +++ b/drivers/fastboot/fb_block.c
> @@ -11,6 +11,7 @@
>  #include <image-sparse.h>
>  #include <malloc.h>
>  #include <part.h>
> +#include <vsprintf.h>
>  
>  /**
>   * FASTBOOT_MAX_BLOCKS_ERASE - maximum blocks to erase per derase call
> @@ -124,6 +125,79 @@ static lbaint_t fb_block_sparse_reserve(struct sparse_storage *info,
>  	return blkcnt;
>  }
>  
> +/**
> + * parse_device_partition() - Parse device:partition format
> + * @part_name: Input string in format "N:partition" or "partition"
> + * @device: Output device number
> + * @partition_name: Output partition name pointer
> + *
> + * Parses the input string to extract device number and partition name.
> + * If no device is specified, uses the default from config.
> + */
> +static void parse_device_partition(const char *part_name, int *device,
> +				   const char **partition_name)
> +{
> +	const char *colon_pos;
> +
> +	/* Default: no device specified, use config default */
> +	*device = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
> +				     CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID, -1);
> +	*partition_name = part_name;
> +
> +	/* Override if device:partition format detected */
> +	colon_pos = strchr(part_name, ':');
> +	if (colon_pos && colon_pos > part_name) {
> +		*device = simple_strtoul(part_name, NULL, 10);
> +		*partition_name = colon_pos + 1;
> +	}
> +}
> +
> +/**
> + * get_block_device() - Get block device descriptor
> + * @interface: Block interface name (e.g., "mmc", "scsi")
> + * @device: Device number
> + * @response: Fastboot response buffer
> + *
> + * Returns: Block device descriptor or NULL on error
> + */
> +static struct blk_desc *get_block_device(const char *interface, int device,
> +					 char *response)
> +{
> +	struct blk_desc *dev_desc;
> +
> +	if (!interface || !strcmp(interface, "")) {
> +		fastboot_fail("block interface isn't provided", response);
> +		return NULL;
> +	}
> +
> +	dev_desc = blk_get_dev(interface, device);
> +	if (!dev_desc)
> +		fastboot_fail("no such device", response);
> +
> +	return dev_desc;
> +}
> +
> +/**
> + * is_partition_table_name() - Check if name matches partition table target
> + * @part_name: Partition name to check
> + * @table_name: Config name for partition table (e.g., "gpt", "mbr")
> + *
> + * Returns: true if part_name matches table_name (with or without device prefix)
> + */
> +static bool is_partition_table_name(const char *part_name, const char *table_name)
> +{
> +	const char *colon_pos;
> +
> +	if (strcmp(part_name, table_name) == 0)
> +		return true;
> +
> +	colon_pos = strchr(part_name, ':');
> +	if (colon_pos && strcmp(colon_pos + 1, table_name) == 0)
> +		return true;

What happens if part_name is ":gpt" ?

In this case, is_partition_table_name returns true but ":gpt" is invalid
because we don't have a device prefix.

Could we use the same logic as in parse_device_partition() ?

> +
> +	return false;
> +}
> +
>  int fastboot_block_get_part_info(const char *part_name,
>  				 struct blk_desc **dev_desc,
>  				 struct disk_partition *part_info,
> @@ -133,25 +207,21 @@ int fastboot_block_get_part_info(const char *part_name,
>  	const char *interface = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
>  						   CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
>  						   NULL);
> -	const int device = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
> -					      CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID, -1);
> +	int device;
> +	const char *partition_name;
>  
>  	if (!part_name || !strcmp(part_name, "")) {
>  		fastboot_fail("partition not given", response);
>  		return -ENOENT;
>  	}
> -	if (!interface || !strcmp(interface, "")) {
> -		fastboot_fail("block interface isn't provided", response);
> -		return -EINVAL;
> -	}
>  
> -	*dev_desc = blk_get_dev(interface, device);
> -	if (!dev_desc) {
> -		fastboot_fail("no such device", response);
> +	parse_device_partition(part_name, &device, &partition_name);
> +
> +	*dev_desc = get_block_device(interface, device, response);
> +	if (!*dev_desc)
>  		return -ENODEV;
> -	}
>  
> -	ret = part_get_info_by_name(*dev_desc, part_name, part_info);
> +	ret = part_get_info_by_name(*dev_desc, partition_name, part_info);
>  	if (ret < 0)
>  		fastboot_fail("failed to get partition info", response);
>  
> @@ -310,12 +380,114 @@ void fastboot_block_write_sparse_image(struct blk_desc *dev_desc, struct disk_pa
>  		fastboot_okay(NULL, response);
>  }
>  
> +#if CONFIG_IS_ENABLED(EFI_PARTITION)
> +/**
> + * flash_gpt_partition_table() - Flash GPT partition table
> + * @part_name: Partition name (format: "gpt" or "N:gpt")
> + * @download_buffer: Buffer containing GPT data
> + * @response: Fastboot response buffer
> + */
> +static void flash_gpt_partition_table(const char *part_name, void *download_buffer,
> +				      char *response)
> +{
> +	const char *interface = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
> +						   CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
> +						   NULL);
> +	struct blk_desc *dev_desc;
> +	int device;
> +	const char *partition_name;
> +
> +	parse_device_partition(part_name, &device, &partition_name);

partition_name is not used in this function. Could we maybe rework
parse_device_partition so that we don't always need partition_name ?

> +
> +	dev_desc = get_block_device(interface, device, response);
> +	if (!dev_desc)
> +		return;
> +
> +	printf("%s: updating MBR, Primary and Backup GPT(s) on %s device %d\n",
> +	       __func__, interface, dev_desc->devnum);
> +
> +	if (is_valid_gpt_buf(dev_desc, download_buffer)) {
> +		printf("%s: invalid GPT - refusing to write to flash\n", __func__);
> +		fastboot_fail("invalid GPT partition", response);
> +		return;
> +	}
> +
> +	if (write_mbr_and_gpt_partitions(dev_desc, download_buffer)) {
> +		printf("%s: writing GPT partitions failed\n", __func__);
> +		fastboot_fail("writing GPT partitions failed", response);
> +		return;
> +	}
> +
> +	part_init(dev_desc);
> +	printf("........ success\n");
> +	fastboot_okay(NULL, response);
> +}

This function is very similar to what we have in
fastboot_mmc_flash_write().

Can we please update fastboot_mmc_flash_write() to reuse this to avoid
code duplication?

> +#endif
> +
> +#if CONFIG_IS_ENABLED(DOS_PARTITION)
> +/**
> + * flash_mbr_partition_table() - Flash MBR partition table
> + * @part_name: Partition name (format: "mbr" or "N:mbr")
> + * @download_buffer: Buffer containing MBR data
> + * @response: Fastboot response buffer
> + */
> +static void flash_mbr_partition_table(const char *part_name, void *download_buffer,
> +				      char *response)
> +{
> +	const char *interface = config_opt_enabled(CONFIG_FASTBOOT_FLASH_BLOCK,
> +						   CONFIG_FASTBOOT_FLASH_BLOCK_INTERFACE_NAME,
> +						   NULL);
> +	struct blk_desc *dev_desc;
> +	int device;
> +	const char *partition_name;
> +
> +	parse_device_partition(part_name, &device, &partition_name);
> +
> +	dev_desc = get_block_device(interface, device, response);
> +	if (!dev_desc)
> +		return;
> +
> +	printf("%s: updating MBR on %s device %d\n", __func__, interface,
> +	       dev_desc->devnum);
> +
> +	if (is_valid_dos_buf(download_buffer)) {
> +		printf("%s: invalid MBR - refusing to write to flash\n", __func__);
> +		fastboot_fail("invalid MBR partition", response);
> +		return;
> +	}
> +
> +	if (write_mbr_sector(dev_desc, download_buffer)) {
> +		printf("%s: writing MBR partition failed\n", __func__);
> +		fastboot_fail("writing MBR partition failed", response);
> +		return;
> +	}
> +
> +	part_init(dev_desc);
> +	printf("........ success\n");
> +	fastboot_okay(NULL, response);
> +}
> +#endif

Same here.

> +
>  void fastboot_block_flash_write(const char *part_name, void *download_buffer,
>  				u32 download_bytes, char *response)
>  {
>  	struct blk_desc *dev_desc;
>  	struct disk_partition part_info;
>  
> +#if CONFIG_IS_ENABLED(EFI_PARTITION)
> +	if (is_partition_table_name(part_name, CONFIG_FASTBOOT_GPT_NAME)) {
> +		flash_gpt_partition_table(part_name, download_buffer, response);
> +		return;
> +	}
> +#endif
> +
> +#if CONFIG_IS_ENABLED(DOS_PARTITION)
> +	if (is_partition_table_name(part_name, CONFIG_FASTBOOT_MBR_NAME)) {
> +		flash_mbr_partition_table(part_name, download_buffer, response);
> +		return;
> +	}
> +#endif
> +
>  	if (fastboot_block_get_part_info(part_name, &dev_desc, &part_info, response) < 0)
>  		return;
>  
> @@ -326,4 +498,4 @@ void fastboot_block_flash_write(const char *part_name, void *download_buffer,
>  		fastboot_block_write_raw_image(dev_desc, &part_info, part_name,
>  					       download_buffer, download_bytes, response);
>  	}
> -}
> +}
> \ No newline at end of file

Nitpick: this change is not needed, please drop


>
> -- 
> 2.34.1

[PATCH 2/2] doc: fastboot: Document block device selection syntax

[Balaji Selvanathan]

Add documentation for the device selection syntax in fastboot
block device operations. Users can now specify target devices
using "N:partition" format where N is the device number.

Document usage examples for regular partition operations like
"fastboot flash 0:boot boot.img" and partition table operations
like "fastboot flash 1:gpt gpt.img". When no device number is
specified, the default from CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID
is used.

Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
---
 doc/android/fastboot.rst | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/doc/android/fastboot.rst b/doc/android/fastboot.rst
index 19e2ee9d407..ce3a030e701 100644
--- a/doc/android/fastboot.rst
+++ b/doc/android/fastboot.rst
@@ -147,6 +147,38 @@ The Fastboot implementation in U-Boot allows to write images into disk
 partitions. Target partitions are referred on the host computer by
 their names.
 
+Device Selection for Block Devices
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When using ``FASTBOOT_FLASH_BLOCK``, you can specify which block device to
+target by prefixing the partition name with the device number and a colon.
+
+Syntax::
+
+    <device_number>:<partition_name>
+
+Examples::
+
+    fastboot flash 0:boot boot.img        # Flash to device 0, partition "boot"
+    fastboot flash 1:system system.img    # Flash to device 1, partition "system"
+    fastboot flash 0:gpt gpt.img          # Write GPT to device 0
+    fastboot flash 1:mbr mbr.img          # Write MBR to device 1
+
+If no device number is specified, the default device from
+``CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID`` is used::
+
+    fastboot flash boot boot.img          # Uses default device
+
+This syntax is supported for:
+
+* Regular partition flashing
+* GPT partition table updates (``gpt`` or ``N:gpt``)
+* MBR partition table updates (``mbr`` or ``N:mbr``)
+* Partition erasing operations
+
+Partition Name Formats
+^^^^^^^^^^^^^^^^^^^^^^
+
 For GPT/EFI the respective partition name is used.
 
 For MBR the partitions are referred by generic names according to the
@@ -186,6 +218,15 @@ configuration options:
    CONFIG_FASTBOOT_GPT_NAME
    CONFIG_FASTBOOT_MBR_NAME
 
+When using block devices (``FASTBOOT_FLASH_BLOCK``), you can specify the target
+device by prefixing with the device number::
+
+   fastboot flash 0:gpt gpt.img    # Write GPT to device 0
+   fastboot flash 1:mbr mbr.img    # Write MBR to device 1
+
+If no device number is specified, the default device from
+``CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID`` is used.
+
 In Action
 ---------
 

-- 
2.34.1

Re: [PATCH 2/2] doc: fastboot: Document block device selection syntax

[Mattijs Korpershoek]

Hi Balaji,

Thank you for the patch.

On Fri, Apr 10, 2026 at 10:12, Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com> wrote:

> Add documentation for the device selection syntax in fastboot
> block device operations. Users can now specify target devices
> using "N:partition" format where N is the device number.
>
> Document usage examples for regular partition operations like
> "fastboot flash 0:boot boot.img" and partition table operations
> like "fastboot flash 1:gpt gpt.img". When no device number is
> specified, the default from CONFIG_FASTBOOT_FLASH_BLOCK_DEVICE_ID
> is used.
>
> Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>

> ---