[U-Boot] [RFC] testing mmc slot w/ generic mmc

[Michael Jones <michael.jones@matrix-vision.de>]

I have a custom OMAP3-based board with 2 MMC slots.  During my boot
sequence, I want to test whether a card is present in mmc slot 1, and
boot from it if so.  Otherwise it will continue to look at other
options.  Until now, w/o CONFIG_GENERIC_MMC, I have used 'mmc init 1' to
do this, which would return false if there was no card.  It sounds like
I should be using generic MMC, so now I'm trying to change my boot
script to use the generic mmc commands.  However, none of them (aside
from read/write) seems to return false just because there is no card.  A
workaround of course is to just try to read from it.

Wouldn't it make sense for 'mmc dev N', or at least 'mmc rescan' to
return failed if there's no card in slot N?  Or is there a use case for
setting the current MMC device to an empty slot?  They both call
mmc_init(), which returns UNUSABLE_ERR, but this is ignored.  I would
like them to return 1 when mmc_init() fails.

Sound reasonable?  Or is there already a better way to test whether an
mmc slot is populated?

Am I supposed to wait until the next merge window to submit such a patch
for review?

-Michael

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