Hi Stéphane,
Thanks for reporting this bug. Could you try using the modesetting driver
instead of fbdev.

Also, I think this is solved by the following patch:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=61bb3fea44b71dd9935227920b036fdb96936f4d

So if you could try 3.10-rc7 while still using fbdev and report back, that
would be great.

-Patrik