Hey Kukjin, Andrzej,
     I recently started playing around with functionfs, and have noticed 
some strange behavior with my origen board.

If I enable the FunctionFS gadget driver, I see the board hang at boot here:

[    2.360000] USB Mass Storage support registered.
[    2.365000] s3c-hsotg s3c-hsotg: regs f0040000, irq 103
[    2.375000] s3c-hsotg s3c-hsotg: EPs:15
[    2.380000] s3c-hsotg s3c-hsotg: dedicated fifos
[    2.385000] g_ffs: file system registered
[    2.390000] mousedev: PS/2 mouse device common for all mice
[    2.395000] s5p-fimc exynos4-fimc.0: start latency exceeded, new 
value 792 ns
[    2.400000] s5p-fimc exynos4-fimc.0: state restore latency exceeded, 
new vals
[    2.410000] s5p-fimc exynos4-fimc.0: stop latency exceeded, new value 
667 ns
[    2.420000] s5p-fimc exynos4-fimc.0: state save latency exceeded, new 
value s
[    2.425000] s5p-fimc exynos4-fimc.1: start latency exceeded, new 
value 625 ns
[    2.435000] s5p-fimc exynos4-fimc.1: state restore latency exceeded, 
new vals
[    2.440000] s5p-fimc exynos4-fimc.1: stop latency exceeded, new value 
750 ns
[    2.450000] s5p-fimc exynos4-fimc.1: start latency exceeded, new 
value 667 ns
[    2.455000] s5p-fimc exynos4-fimc.1: state save latency exceeded, new 
value s


And it gets no further. Trying to send a sysrq-t (or anything after a 
break) doesn't seem to do anything either.

Trying to debug this a bit more, I added "initcall_debug 
ignore_loglevel" to the boot arguments, but strangely, that allows it to 
boot and everything seems to be fine. I added a number of printks to the 
g_ffs driver, but it doesn't seem like the hang is happening in that 
code (though de-configuring it does avoid the issue - so maybe not?).

So there's probably some sort of race going on, and was curious if you 
had any thoughts on how to further narrow it down.

This is against 3.8 vanilla. With the attached config.
bootarguments:
"console=tty0 console=ttySAC2,115200n8 rootwait ro init=/init 
androidboot.console=ttySAC2 console=ttySAC2 root=/dev/mmcblk0p2"

thanks
-john