On 03/19/2014 02:50 PM, Viresh Kumar wrote: > 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. > > 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? Sorry, for a moment I got confused and thought that your patch addresses the race conditions present in normal drivers alone, and not ASYNC_NOTIFICATION drivers. But now I understand that your patch intends to fix both the problems at once. I'll share my thoughts about the design in a separate reply. Regards, Srivatsa S. Bhat -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
