[U-Boot] Are mmc open/close subcommands needed?

[Hector Palacios]

Dear Otavio,

On 01/03/2014 06:35 PM, Otavio Salvador wrote:
> On Thu, Jan 2, 2014 at 9:36 PM, Marek Vasut <marex at denx.de> wrote:
>> On Thursday, January 02, 2014 at 05:53:00 PM, Hector Palacios wrote:
>>> Hi,
>>>
>>> I saw commit 2a91c9134675140853577b565210458b5774e6cf that introduces mmc
>>> subcommands 'open' and 'close' to access eMMC boot partitions and was
>>> wondering if they are really needed. Can't the same be achieved with
>>> already existing 'mmc dev [dev] [part]' command?
>>>
>>> mmc open <dev> <boot_partition>
>>>    is the same as
>>> mmc dev <dev> <part>
>>>    where <part> is the boot partition
>>>
>>> mmc close <dev> <boot_partition>
>>>    is the same as
>>> mmc dev <dev> 0
>>>    as a 0 will switch to partition 0 (user data).
>>>
>>> Best regards,
>>> --
>>> Hector Palacios
>>
>> +CC Panto
>
> No; this is for different use.
>
> The open and close are to open the Boot partitions part of eMMC 4; by
> default those eMMC will be using the user partitions, not the boot
> area.
>
> The nice, and confusing thing, is that those boot partitions also
> start in address 0 as a 'virtual disk'.

I don't think they are different commands that do the same by coincidence. The 'mmc 
dev' command, when passed a fourth argument for the partition is calling the function 
'mmc_switch_part()'.
This function executes the CMD6 command to write the Extended CSD register 
PARTITION_CONFIG field that gives you access to any MMC partition (user data area, 
boot partitions 1 and 2, RPMB, General Purpose 1-4 partitions).

It doesn't look like specific eMMC commands are needed to access the boot partitions, 
but maybe I'm misinterpreting the code.

Best regards,
--
Hector Palacios