On 19 March 2014 14:47, Srivatsa S. Bhat srivatsa.bhat@linux.vnet.ibm.com wrote:
Wait, I think I remember. The problem was about dealing with drivers that do asynchronous notification (those that have the ASYNC_NOTIFICATION flag set). In particular, exynos-5440 driver sends out the POSTCHANGE notification from a workqueue worker, much later than sending the PRECHANGE notification.
From what I saw, this is how the exynos-5440 driver works:
->target() is invoked, and the driver writes to a register and returns to its caller.
An interrupt occurs that indicates that the frequency was changed.
The interrupt handler kicks off a worker thread which then sends out the POSTCHANGE notification.
Correct!!
So the important question here is, how does the exynos-5440 driver protect itself from say 2 ->target() calls which occur in close sequence (before allowing the entire chain for the first call to complete)?
As far as I can see there is no such synchronization in the driver at the moment. Adding Amit to CC for his comments.
Yes, and that's what my patch is trying to fix. Where is the confusion?