Re: [RFC V2] cpufreq: make sure frequency transitions are serialized

From: Viresh Kumar
Date: Wed Mar 19 2014 - 05:20:47 EST

On 19 March 2014 14:47, Srivatsa S. Bhat
<srivatsa.bhat@xxxxxxxxxxxxxxxxxx> 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.


> 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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