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

[Ziyuan]

hi Stephen,

On 03/14/2017 05:49 AM, 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.

The 4th of "mmc dev 0 1" is the *software* partition index, not the hw 
partition index. AKA eMMC has four partitions: user 
data/boot0/boot1/rpmb, I think Tim wanna to boot from other partition, 
like boot0, right?

As the eMMC spec v5.1 said that, you can do the following steps:
1, set BOOT_PARTITION_ENABLE bit
2, send cmd0 w/ argument 0xFFFFFFFA
3,After putting a slave into transfer state, master sends CMD6 (SWITCH) 
to set the PARTITION_ACCESS bits in the EXT_CSD register, byte [179]

I don't try to boot from boot partitions, I hope it makes sense to you.
>
> 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.
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