linux/drivers/mmc/card
Ulf Hansson 9aaf3437aa mmc: block: Use the mmc host device index as the mmcblk device index
Commit 520bd7a8b4 ("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.

As the above commit significantly improves boot time for some platforms
(magnitude of seconds), let's avoid reverting this change but instead
restore the behaviour of how mmcblk device indexes becomes picked.

By using the same index for the mmcblk device as for the corresponding mmc
host device, the probe order of mmc host devices decides the index we get
for the mmcblk device.

For those platforms that suffers from a regression, one could expect that
this updated behaviour should be sufficient to meet their expectations of
"fixed" mmcblk device indexes.

Another side effect from this change, is that the same index is used for
the mmc host device, the mmcblk device and the mmc block queue. That
should clarify their relationship.

Reported-by: Peter Hurley <peter@hurleysoftware.com>
Reported-by: Laszlo Fiat <laszlo.fiat@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: 520bd7a8b4 ("mmc: core: Optimize boot time by detecting cards
simultaneously")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
2016-04-14 11:39:34 +02:00
..
block.c mmc: block: Use the mmc host device index as the mmcblk device index 2016-04-14 11:39:34 +02:00
Kconfig tty: Added a CONFIG_TTY option to allow removal of TTY 2013-01-18 16:15:27 -08:00
Makefile mmc: Makefile: Fix EXTRA_CFLAGS assignment 2010-10-23 21:11:15 +08:00
mmc_test.c mmc: mmc_test: mention that '0' runs all tests 2016-02-29 11:02:54 +01:00
queue.c scatterlist: remove open coded sg_unmark_end instances 2015-08-17 08:12:56 -06:00
queue.h mmc: block: Retry errored data requests when re-tuning is needed 2015-06-01 09:06:59 +02:00
sdio_uart.c tty: Use termios c_*flag macros 2016-01-28 14:13:44 -08:00