Real time ioctls such as buffer operations and registers configuration updates are timing critical. Other ioctls such as ISP stream start/stop could take longer time to finish because the ioctl blocks until the hardware start/stop streaming completely. Using a separate mutex will prevent real time operations from starving and results in framedrop. Change-Id: I3421b596bde53198ba4df7da9636441762c739db Signed-off-by: Kevin Chan <ktchan@codeaurora.org>