[U-Boot] accessing eMMC boot partitions from U-Boot

[Stephen Warren]

On 03/13/2017 07:08 PM, Sergey Kubushyn wrote:
> On Mon, 13 Mar 2017, Stephen Warren wrote:
>
>> On 03/13/2017 03:34 PM, Tim Harvey wrote:
>>>  Greetings,
>>>
>>>  I'm working with some boards with eMMC FLASH and understand that I can
>>>  set the fields of the PARTITION_CONFIG with the 'mmc partconf' command
>>>  to specify what partition is used for boot. Once I do that to set the
>>>  boot0 partition for example, how can I access that  partition from
>>>  within u-boot via mmc read/write? In Linux the kernel provides access
>>>  to user/boot0/boot1/rpmb via different devices, but I don't see u-boot
>>>  doing that.
>>
>> The "mmc dev" command can be used to select which MMC device to
>> operate on. The "typical" command "mmc dev 0" selects the main
>> partition on MMC device 0 for later MMC-specific commands such as "mmc
>> read". You can add an extra parameter to that command to request a
>> specific HW partition, e.g. "mmc dev 0 1" selects boo0 of MMC device 0
>> and "mmc dev 0 2" selects boot1.
>>
>> A similar naming scheme exists for commands that take a complete
>> device specification each time. For example, "part list mmc 0" to list
>> partitions in the main partition on MMC device 0, or "part list mmc
>> 0.1" to list partitions on boot0 of MMC device 0.
>
> Unfortunately this has absolutely nothing to do with eMMC _BOOT_
> partitions...

That's incorrect. See my other reply for details.

> There 2 of those on eMMC and they are _NOT_ accessible in
> this fashion. Neither they bear any FS on them.

The boot HW partitions are block storage just like any other. SW can 
place whatever data structures it wants into these HW partitions; the 
interpretation of any data stored here is up to the SW or HW that reads 
and interprets it, e.g. a SoC boot ROM. While many systems will place 
raw data here, others certainly do place SW partition tables, and 
perhaps even filesystems, in the HW partitions.