[U-Boot] [PATCH 0/2] fix issue with mmc partition management

[Tom Rini]

On Tue, Sep 02, 2014 at 06:31:21PM -0500, Peter A. Bigot wrote:

> This series aims at addressing an issue discovered with SPL mode when
> the MMC device being used lacks an environment partition.
> http://www.mail-archive.com/meta-ti@yoctoproject.org/msg04320.html
> includes details on the original failure with this diagnosis:
> 
>   This is a bug in handling mmc_switch_part: what's happening is that
>   the code reconfigures the mmc device to look at the partition on which
>   the environment is to be found, but fails to restore it to reflect the
>   state of the whole device. I.e., the mmc capacity and lba are zero in
>   my case (I have no partition 2 on the uSD card), but mmc_switch_part()
>   returns -ENODEV on the attempt to switch back in fini_mmc_for_env()
>   without also resetting the capacity to what the rest of the system
>   expects.

1/2 has been superseded and there's some questions about 2/2.  I'm going
to take 2/2 as it fixes a real problem.  But Stephen brings up some good
questions that do need to be answered.  The first thing is that SPL
today assumes that it only has one MMC device registered with the
subsystem, not 2.  This may be reworkable (and maybe not have a big size
change) but it's a bit late in this release cycle for that.  So what
this means is that on some hardware like say Beaglebone Black we either
have an SD card (which lacks physical partitions) or we have an eMMC
which means the 2 boot partitions and the user partition.

The next part of the problem is that we have some cases where we say
"environment is on eMMC, in one of the boot partitions" and we say "SPL
needs to look at the environment".  This situation works fine when we
boot from eMMC.  Things fail when we use this same binary to boot from
SD card.  We don't have env and somewhere along the line what fails is
that we tried to switch physical partition, noticed a failure, tried to
correct said failure but instead end up with our internal representation
of the SD/MMC device being invalid.  Peter's patch 2/2 corrects this so
that when we hit a failure it goes and re-sets that representation.

But the next question is "wait, why did it get set _wrong_ to start
with?".  I'm not sure actually.  The fini_mmc_for_env call isn't making
us be restored to what the physical partition was before, if that's what
it was intended to do, it's making sure that we're still on the env
partition.  Which I'm not sure why it needs to do since we've already
read a copy into memory at this point.

-- 
Tom
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