[3.14] Initialize MMC devices in predictable order #57
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… is already set to a correct value after a call to mmc_host_alloc()
Commit 520bd7a ("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 <[email protected]> Reported-by: Laszlo Fiat <[email protected]> Cc: Linus Torvalds <[email protected]> Fixes: 520bd7a ("mmc: core: Optimize boot time by detecting cards simultaneously") Cc: <[email protected]> Signed-off-by: Ulf Hansson <[email protected]>
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Tested this commit on a eMMC only ODROID C2, and mmcblk0 found in the following file has to be changed to mmcblk1 https://github.com/LibreELEC/LibreELEC.tv/blob/master/projects/Odroid_C2/bootloader/boot.ini#L13 However once mmcblk0 is changed to mmcblk1 - a micro SDHC LE only image refuses to boot. Please do NOT merge this. |
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Make sure MMC devices (mmcblkX) always get predictable index (in the order they are defined in device tree).
Because MMC devices are initialized asynchronously to optimize boot time, we cannot guarantee mmcblkX will belong to specific MMC device. Amlogic boards usually have /dev/mmcblk0 representing SD card slot. But in some cases if the device has internal eMMC memory, SD-card slot may become /dev/mmcblk1 while /dev/mmcblk0 is assigned to internal eMMC.
This PR makes sure MMC devices are always get indexes assigned in the order they are defined in device tree.