kumquat-buildroot/board/qemu/arm-vexpress/readme.txt
Yann E. MORIN 626c9705d2 board/qemu: ensure root is available before mounting it
On my machine, it happens once in a while that the virtualised machine
boots too fast for the rootfs to be available at the time the kernel
tries to mount it.

For example, board/qemu/arm-vexpress/readme.txt suggested changing
"-smp 1" up to "-smp 4". But doing so here causes a kernel panic:

    VFS: Cannot open root device "mmcblk0" or unknown-block(0,0): error -6
    Please append a correct "root=" boot option; here are the available partitions:
    1f00          131072 mtdblock0
     (driver?)
    1f01           32768 mtdblock1
     (driver?)
    Kernel panic - not syncing: VFS: Unable to mount root fs on
    unknown-block(0,0)

So, add the oh-so-useful 'rootwait' option to all kernel command lines
for qemu defconfigs.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Joel Stanley <joel@jms.id.au>
Cc: Mark Corbin <mark.corbin@embecosm.com>
Cc: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
2019-06-25 22:55:58 +02:00

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Run the emulation with:
qemu-system-arm -M vexpress-a9 -smp 1 -m 256 -kernel output/images/zImage -dtb output/images/vexpress-v2p-ca9.dtb -drive file=output/images/rootfs.ext2,if=sd,format=raw -append "console=ttyAMA0,115200 rootwait root=/dev/mmcblk0" -serial stdio -net nic,model=lan9118 -net user
The login prompt will appear in the terminal that started Qemu. The
graphical window is the framebuffer.
If you want to emulate more cores change "-smp 1" to "-smp 2" for
dual-core or even "smp -4" for a quad-core configuration.
Tested with QEMU 2.12.0