On Sat, Jun 25, 2016 at 12:48:53AM +0100, peter green wrote:
> While upgrading a wandboard quad from 4.4 to 4.6 (debian armmp kernels) I
> got a boot failure. I tracked this down to the device name for the SD card
> changing from mmcblk0 to mmcblk2
>
> Any idea why this has changed? There don't seem to be any other
> lower-numbered mmcblk devices.
I think I saw a kernel commit recently that makes the mmcblk# use whate
the number of the controller is. This is a great improvement over the
random order they were in for many years. In the past they used to be
probed in controller order, so they were predictable.
See:
commit 9aaf3437aa72ed5370bf32c99580a3fa2c330e3d
Author: Ulf Hansson <ulf.hans...@linaro.org>
Date: Wed Apr 6 16:12:08 2016 +0200
mmc: block: Use the mmc host device index as the mmcblk device index
Commit 520bd7a8b415 ("mmc: core: Optimize boot time by detecting cards
simultaneously") causes regressions for some platforms.
These platforms relies on fixed mmcblk device indexes, instead of
deploying the defacto standard with UUID/PARTUUID. In other words their
rootfs needs to be available at hardcoded paths, like /dev/mmcblk0p2.
Such guarantees have never been made by the kernel, but clearly the above
commit changes the behaviour. More precisely, because of that the order
changes of how cards becomes detected, so do their corresponding mmcblk
device indexes.
[...]
So this should be "new" in 4.6 versus 4.5 or earlier kernels.
--
Len Sorensen
