On 11/07/2014 10:07 AM, Alexandre Courbot wrote: > On 10/29/2014 11:50 PM, Tomeu Vizoso wrote: >> Hello, >> >> these patches implement support for setting the rate of the EMC clock based on >> stats collected from the ACTMON, a piece of hw in the Tegra124 that counts >> memory accesses (among others). >> >> It depends on the following in-flight patches: >> >> * MC driver: http://thread.gmane.org/gmane.linux.ports.tegra/19623 >> * EMC driver: http://thread.gmane.org/gmane.linux.ports.arm.kernel/365125 >> * CPUFreq driver: http://thread.gmane.org/gmane.linux.kernel/1812962 >> >> I have pushed a branch here for testing: > > I am not too familiar with DVFS, but after going through this series it > really seems to me that this could use devfreq. In its current form this > driver mixes control and policy and lacks flexibility, preventing e.g. > to switch to a performance or power-saving profile. Could you study the > feasibility of using devfreq for this? Yeah, I started writing a devfreq driver, but then I looked in more detail to the downstream driver and realized that most of the functionality that devfreq provides overlaps with the hw. The ACTMON can be configured to fire an interrupt when a set of thresholds are crossed, similar to the simple-ondemand governor but a bit more sophisticated. The only functionality of the governors that isn't covered by the ACTMON hw is determining the new frequency after a threshold has been crossed, but if we want to retain the flexibility of the downstream solution, we would need to write a new governor anyway. I realize that it would be cool to reuse the code in devfreq, but being able to let the hw sample the counters, calculating averages and checking if a threshold has been crossed without the cpu having to intervene gives this SoC quite an edge when compared to its competitors. Regards, Tomeu -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
