On Mon, 2015-09-07 at 18:23 +0200, Mian Yousaf Kaukab wrote:
> urb completion callback is executed in host controllers interrupt
> context. To keep preempt disable time short, add urbs to a list on
> completion and schedule work to process the list.
>
> Moreover, save timestamp and sof number in the urb completion callback
> to avoid any delays.
>
> Signed-off-by: Mian Yousaf Kaukab <yousaf.kau...@intel.com>
> ---
> History:
> v1:
> - Use global work queue instead of creating ordered queue.
1. using a common queue for real-time work is probably not nice for
picture quality
2. it will deadlock under some conditions
The explanation is a bit long
Suppose we have a device with a camera and a storage device,
like an ordinary camera you can use as a video device which also
exports its memory card.
Now we assume that the storage part is suspended.
CPU A CPU B
work item scheduled
entering uvc_uninit_video()
work item executed
work item allocates memory
write to storage interface
storage interface being resumed
flush_work() - waiting for CPU B
DEADLOCK
If you want to use flush_work() you must use a dedicated queue.
Regards
Oliver
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