Hi Stephen, On Tue, Jan 25, 2022 at 03:15:39PM +0100, Maxime Ripard wrote: > Hi, > > This is a follow-up of the discussion here: > https://lore.kernel.org/linux-clk/20210319150355.xzw7ikwdaga2dwhv@gilmour/ > > and here: > https://lore.kernel.org/all/20210914093515.260031-1-maxime@xxxxxxxxxx/ > > While the initial proposal implemented a new API to temporarily raise and lower > clock rates based on consumer workloads, Stephen suggested an > alternative approach implemented here. > > The main issue that needed to be addressed in our case was that in a > situation where we would have multiple calls to clk_set_rate_range, we > would end up with a clock at the maximum of the minimums being set. This > would be expected, but the issue was that if one of the users was to > relax or drop its requirements, the rate would be left unchanged, even > though the ideal rate would have changed. > > So something like > > clk_set_rate(user1_clk, 1000); > clk_set_min_rate(user1_clk, 2000); > clk_set_min_rate(user2_clk, 3000); > clk_set_min_rate(user2_clk, 1000); > > Would leave the clock running at 3000Hz, while the minimum would now be > 2000Hz. > > This was mostly due to the fact that the core only triggers a rate > change in clk_set_rate_range() if the current rate is outside of the > boundaries, but not if it's within the new boundaries. > > That series changes that and will trigger a rate change on every call, > with the former rate being tried again. This way, providers have a > chance to follow whatever policy they see fit for a given clock each > time the boundaries change. > > This series also implements some kunit tests, first to test a few rate > related functions in the CCF, and then extends it to make sure that > behaviour has some test coverage. As far as I know, this should address any concern you had with the previous iterations. Is there something else you'd like to see fixed/improved? Maxime
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