After a lot of testing, and some more confusion, I have managed to get the Rock2 to boot using the latest (2016.03-rc3) version of U-Boot, and the latest kernel (4.5-rc7)

As previously, there was a lot of conflicting information…….

I started by booting into the semi-proprietary 3.10-based kernel on the SDcard, and then erasing the eMMC (dd if=/dev/zero… etc..).

I managed to get U-Boot to load and run, but the kernel stubbornly refused to load.. I did find some ‘successful’ boot examples using the 4.5-rc kernel, but these all booted onto a ramdisk image (/dev/ram0). (See https://kernelci.org/boot/rk3288-rock2-square/ )

I modified the kernel config and commandline parameters from these examples, and the combination booted into the SDcard successfully:

U-Boot SPL 2016.03-rc3 (Mar 05 2016 - 17:11:08)
Trying to boot from MMC

U-Boot 2016.03-rc3 (Mar 05 2016 - 17:11:08 -0800)

Model: Radxa Rock 2 Square
DRAM: 2 GiB
MMC: dwmmc@ff0f0000: 0, dwmmc@ff0c0000: 1
stdio_add_devices: Video device failed (ret=-1)
In: serial
Out: serial
Err: serial
Net: Net Initialization Skipped
No ethernet found.
Hit any key to stop autoboot: 0
=> boot
6721600 bytes read in 594 ms (10.8 MiB/s)
31421 bytes read in 36 ms (851.6 KiB/s)
Kernel image @ 0x2000000 [ 0x000000 - 0x669040 ]
## Flattened Device Tree blob at 01f00000
 Booting using the fdt blob at 0x1f00000
 Loading Device Tree to 1fff5000, end 1ffffabc ... OK

Starting kernel ...

[ 0.000000] Booting Linux on physical CPU 0x500
[ 0.000000] Linux version 4.5.0-rc7 (root@rgrock2) (gcc version 5.3.1 20151207 (Red Hat 5.3.1-2) (GCC) ) #1 SMP Sun Mar 13 13:32:42 EDT 2016
[ 0.000000] CPU: ARMv7 Processor [410fc0d1] revision 1 (ARMv7), cr=10c5387d
[ 0.000000] CPU: div instructions available: patching division code
[ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
[ 0.000000] Machine model: Radxa Rock 2 Square
[ 0.000000] debug: ignoring loglevel setting.
[ 0.000000] cma: Reserved 64 MiB at 0x7c000000
[ 0.000000] Memory policy: Data cache writealloc
[ 0.000000] On node 0 totalpages: 524288
[ 0.000000] free_area_init_node: node 0, pgdat c108d640, node_mem_map eeff9000
[ 0.000000] DMA zone: 1536 pages used for memmap
[ 0.000000] DMA zone: 0 pages reserved
[ 0.000000] DMA zone: 196608 pages, LIFO batch:31
[ 0.000000] HighMem zone: 327680 pages, LIFO batch:31
[ 0.000000] PERCPU: Embedded 12 pages/cpu @eefa5000 s18880 r8192 d22080 u49152
[ 0.000000] pcpu-alloc: s18880 r8192 d22080 u49152 alloc=12*4096
[ 0.000000] pcpu-alloc: [0] 0 [0] 1 [0] 2 [0] 3
[ 0.000000] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 522752
[ 0.000000] Kernel command line: console=ttyS2,115200n8 root=/dev/mmcblk1p1 earlyprintk ignore_loglevel
[ 0.000000] PID hash table entries: 4096 (order: 2, 16384 bytes)
[ 0.000000] Dentry cache hash table entries: 131072 (order: 7, 524288 bytes)
[ 0.000000] Inode-cache hash table entries: 65536 (order: 6, 262144 bytes)
[ 0.000000] Memory: 1998816K/2097152K available (8591K kernel code, 1053K rwdata, 4124K rodata, 1104K init, 343K bss, 32800K reserved, 65536K cma-reserved, 1245184K highmem) ..................................
........................................................
................................
16.210447] rk_gmac-dwmac ff290000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[ 16.219077] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ OK ] Started LSB: Bring up/down networking.
[ OK ] Started /etc/rc.d/rc.local Compatibility.
 Starting Wait for Plymouth Boot Screen to Quit...
 Starting Terminate Plymouth Boot Screen...

Fedora 23 (Twenty Three)
Kernel 4.5.0-rc7 on an armv7l (ttyS2)
.............
# uname -a
Linux rgrock2 4.5.0-rc7 #1 SMP Sun Mar 13 13:32:42 EDT 2016 armv7l armv7l armv7l GNU/Linux

If you do not have an hdmi monitor attached, the u-boot sequence will wait for several seconds, before continuing…

The U-Boot parameters I used were as follows:

setenv autoload no
setenv bootdelay 10
setenv fdt_high 0x1fffffff
setenv bootargs "console=ttyS2,115200n8 root=/dev/mmcblk1p1 earlyprintk ignore_loglevel"
setenv bootcmd "ext4load mmc 1:1 ${kernel_addr_r} boot/uboot/zImage; ext4load mmc 1:1 ${fdt_addr_r} boot/uboot/rk3288-rock2-square.dtb; bootz ${kernel_addr_r} - ${fdt_addr_r}"

One further important thing to mention… The cpu/soc runs _hot_ when under load, so you will need a heatsink! When I first attempted to compile the kernel on the rock2, using the usual multi-cpu make command (make -j5 zImage...) the system shut down and rebooted, and the chipset was _very_ hot.. Until I can make up a suitable heatsink – and maybe even a fan? – I compile in single-processor mode (leave out the -j5..), and this is OK..

Robert Gadsdon. March 13, 2016.