On Fri, Feb 07, 2020 at 01:32:28PM +0100, Ulf Hansson wrote: > [...] > > > > I understand the arguments for using PC vs OSI and agree with it. But > > > what in PSCI is against Linux knowing when the last core is powering > > > down when the PSCI is configured to do only Platform Cordinated. > > > > Nothing :D. But knowing the evolution and reasons for adding OSI in the > > PSCI specification and having argued about benefits of OSI over PC for > > years and finally when we have it in mainline, this argument of using > > PC for exact reasons why OSI evolved is something I can't understand > > and I am confused. > > > > > There should not be any objection to drivers knowing when all the cores > > > are powered down, be it reference counting CPU PM notifications or using > > > a cleaner approach like this where GendPD framwork does everything > > > cleanly and gives a nice callback. ARM architecture allows for different > > > aspects of CPU access be handled at different levels. I see this as an > > > extension of that approach. > > > > > > > One thing that was repeatedly pointed out during OSI patch review was no > > extra overhead for PC mode where firmware can make decisions. So, just > > use OSI now and let us be done with this discussion of OSI vs PC. If PC > > is what you think you need for future, we can revert all OSI changes and > > start discussing again :-) > > Just to make it clear, I fully agree with you in regards to overhead > for PC-mode. This is especially critical for ARM SoCs with lots of > cores, I assume. > > However, the overhead you refer to, is *only* going to be present in > case when the DTS has the hierarchical CPU topology description with > "power-domains". Because, that is *optional* to use, I am expecting > only those SoC/platforms that needs to manage last-man activities to > use this layout, the others will remain unaffected. In PC mode not only there is no need but it is wrong to manage any last-man activity in the kernel. I wonder why we are still talking about this to be honest. Code to handle PSCI platform coordinated mode has been/is in the kernel today and that's all is needed according to the PSCI specifications. Thanks, Lorenzo
