On 20-05-19, 12:47, Nicolas Saenz Julienne wrote: > Hi all, > as some of you may recall I've been spending some time looking into > providing 'cpufreq' support for the Raspberry Pi platform[1]. I think > I'm close to something workable, so I'd love for you to comment on it. > > There has been some design changes since the last version. Namely the > fact that I now make sure *only* the CPU frequency is updated. The > firmware API we use has two modes, with or without turbo. Enabling turbo > implies not only scaling the CPU clock but also the VPU and other > peripheral related clocks. This is problematic as some of them are not > prepared for this kind frequency changes. I spent some time adapting the > peripheral drivers, but the result was disappointing as they poorly > support live frequency changes (which most other chips accept, think for > instance I2C and clock stretching) but also turned out hard to integrate > into the kernel. As we were planning to use 'clk_notifiers' which turns > out not to be such a good idea as it's prone to deadlocks and not > recommended by the clock maintainers[2]. It's also worth mentioning that > the foundation kernel doesn't support VPU frequency scaling either. > > With this in mind, and as suggested by clock maintainers[2], I've > decided to integrate the firmware clock interface into the bcm2835 clock > driver. This, in my opinion, provides the least friction with the > firmware and lets us write very simple and portable higher level > drivers. As I did with the 'cpufreq' driver which simply queries the max > and min frequencies available, which are configurable in the firmware, > to then trigger the generic 'cpufreq-dt'. > > In the future we could further integrate other firmware dependent clocks > into the main driver. For instance to be able to scale the VPU clock, > which should be operated through a 'devfreq' driver. > > This was tested on a RPi3b+ and if the series is well received I'll test > it further on all platforms I own. Please always supply version history on what has changed from V1. And why do you keep sending it as RFC ? Just keep the default PATCH thing, the patches are in good shape I would say. -- viresh
