On Tue, May 26, 2020 at 05:54:20PM +0200, Niklas Cassel wrote: > On Tue, May 26, 2020 at 10:59:48AM +0200, Stephan Gerhold wrote: > > > Considering that CPR is not an actual power domain, CPR gives > > > adjustments to VDD_APC, but I don't know of any other device > > > connected to VDD_APC, other than the CPU, so in hindsight the CPR > > > driver probably should have been implemented using .target_index(), > > > rather than as a power domain provider using performance states. > > > > I suppose having CPR, MEMACC etc as power domain providers is a bit > > overkill, given there is just one consumer. However, at least the > > "performance state" part fits quite well in my opinion. At the end > > all these requirements represent some performance state that must be > > set when the CPU frequency is changed. > > > > For MX, it makes sense to model it as a power domain provider, and for > it to have its own OPP table, since this actually is a power domain. > > For CPR, I think that the target_index() model of just giving an index > in a frequency table is much better, the OPP library can still be used > to get the frequencies/frequency_table. > Since at least for Qualcom CPU's, the corner (opp-level) is defined as > an increasing number 1,2,3,4, without skips. > > Even if it wasn't always without skips, we could just put opp-level in > the CPU opp table, and get it from there. > > The only thing that the corner is used for really, is to use it as an > index the local drv->corner array, which is where the (current) VDD_APC > voltage is stored for each index/corner. > > For CPR, the .target_index() in cpufreq-dt.c gets called, which is > supplied with an index, but the index gets converted to a frequency. > This frequency is then sent to the OPP library, and is then converted > back to an index of the same value (just increased by one), before > cpr_set_performance_state() is called (which then has to subtract one). > In this case, all the extra overhead of going via genpd is totally > unnecessary. > > This is totally correct when setting a performance state on a power > domain like MX, since for an actual power domain you might have > multiple consumers, so you need to go via genpd. > > Considering that CPR is not a power domain, I wish the driver wasn't > designed around performance states, which, _for the CPR case_, > is misleading, unnecessary, and adds extra overhead for no reason. > > I realize the irony of me criticizing my own code. > I simply know better now, and wish I had designed it differently :) > I see what you mean. I'm not sure how much of a problem the "genpd overhead" really is in practice (although I assume it's called quite frequently with a dynamic CPU frequency governor). There is also the argument of it being slightly misleading (because CPR is not actually a real power domain). Speaking of the current solution, I also have to say that (IMO) the device tree binding for "required-opps" is rather confusing and potentially misleading. e.g. for VDD_MX scaling I use required-opps = <&rpmpd_opp_nom>; but looking at just the OPP table absolutely nothing tells me this is supposed to apply to VDD_MX. You actually need to go search for the cpu@ device tree node and then know that some of the power domains there (in some order) are eventually going to be used for the required-opps there. The order is only defined by the qcom-nvmem-cpufreq driver. It took me a few hours to get that right... :) Nevertheless I guess we need a solution for scaling MEMACC without CPR for now. :) I'm not sure if rewriting all this is very realistic (if even possible). So I guess we might be stuck with the genpd approach? Thanks, Stephan
