Messages in this thread | | | Date | Wed, 19 Mar 2014 14:50:37 +0530 | Subject | Re: [RFC V2] cpufreq: make sure frequency transitions are serialized | From | Viresh Kumar <> |
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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: > > 1. ->target() is invoked, and the driver writes to a register and returns > to its caller. > > 2. An interrupt occurs that indicates that the frequency was changed. > > 3. 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?
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