[U-Boot] dra7xx: booting from eMMC raw boot partition

[Michael Pratt]

Hi Richard,

On Wed, Nov 20, 2013 at 5:27 PM, Richard Retanubun
<richardretanubun at ruggedcom.com> wrote:
> However, the CPU does not print anything back on the console...
>
> The only way I can get raw eMMC boot mode to work is if I put the MLO on
> /dev/mmcblk1 (which is the user data area).

I have not seen a reference manual for dra7xx, so this may not apply,
but it is worth noting that many SoCs that support booting from eMMC
do not actually use the boot mode, and simply boot directly from the
user data area.  The boot mode is described in the eMMC spec in a
section titled "Boot operation mode" (Section 7.3 in eMMC 4.4).
Basically, it provides a different initialization sequence that will
sequentially read out the partition selected in CONFIG_PARTITION.  If
the SoC is not utilizing this boot mode, it may unconditionally read
from the user data area.

> Does the MLO for raw boot mode needs to be different that the MLO for raw
> user data area?

If both MLO and U-Boot are to be in the boot partition, booted using
eMMC boot mode, MLO will likely need to behave differently in order to
correctly read U-Boot.  Boot mode sequentially reads out the selected
partition, without using the standard commands, so MLO will need to
understand this and perform the appropriate clocking of the eMMC.  I
am unsure if there is currently support for that.

Hopefully this is helpful!
Michael Pratt