I had been running Kernel 4.6-rc2 on the Radxa Rock2 without any issues, and decided to update to recently-released Kernel 4.6-rc4..

Brief details of changes from -rc3 are here:  http://lkml.iu.edu/hypermail/linux/kernel/1604.2/00610.html

The boot failed, and I then compiled/installed 4.6-rc3 to see if that would have been OK, and it was..

I then noticed something odd in the failed boot process… It appeared that the MMC device references had swapped around in -rc4:

RC3 – and earlier (boot OK):

...........
mmc0: new high speed SDXC card at address e624
mmcblk1: mmc0:e624 SL64G 59.5 GiB
 mmcblk1: p1
...........

RC4 (boot failed):

...........
mmc0: new high speed SDXC card at address e624
mmcblk0: mmc0:e624 SL64G 59.5 GiB
 mmcblk0: p1
...........

So… a simple change to the u-boot kernel boot command – changing root=/dev/mmcblk1p1 to root=/dev/mmcblk0p1 – fixed the problem, and 4.6-rc4 booted OK..

Fedora 23 (Twenty Three)
Kernel 4.6.0-rc4 on an armv7l (ttyS2)
...............
]# uname -a
Linux rgrock2 4.6.0-rc4 #1 SMP Wed Apr 20 18:44:57 EDT 2016 armv7l armv7l armv7l GNU/Linux

All that was needed then, was to change /etc/fstab accordingly.. (Yes – I still use the ‘traditional’ format!)

Initial investigation suggested that this might be the kernel patch responsible:  http://lkml.iu.edu/hypermail/linux/kernel/1604.0/04340.html

On the Rock2, this means that the on-board eMMC is now /dev/mmcblk1, and the SDcard is /dev/mmcblk0…   It will be interesting to see if this change affects any of my other ARM devices…..

Robert Gadsdon. April 20, 2016.