mmc4 以上的partion0 partion1

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mmc4以上的partion0 partion1

这两个是固定的分区，无法格式化，mmc芯片可以设定是从这两个分区启动或user分区启动。需要读写可以参考文件Documentation/mmc/mmc-dev-parts.txt

SD and MMC Device Partitions
============================

Device partitions are additional logical block devices present on the
SD/MMC device.

As of this writing, MMC boot partitions as supported and exposed as
/dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the
parent /dev/mmcblkX.

MMC Boot Partitions
===================

Read and write access is provided to the two MMC boot partitions. Due to
the sensitive nature of the boot partition contents, which often store
a bootloader or bootloader configuration tables crucial to booting the
platform, write access is disabled by default to reduce the chance of
accidental bricking.

To enable write access to /dev/mmcblkXbootY, disable the forced read-only
access with:

echo 0 > /sys/block/mmcblkXbootY/force_ro

To re-enable read-only access:

echo 1 > /sys/block/mmcblkXbootY/force_ro

设置启动位置，即设置ext_sd寄存器，这个寄存器设置后断电不消失。

<CMD state="Updater" type="push" body="$ echo 8 > /sys/devices/platform/sdhci-esdhc-imx.3/mmc_host/mmc0/mmc0:0001/boot_config">enable boot partion 1 to boot</CMD>

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