[PATCH v4 00/10] clk: Improve clock range handling

[Maxime Ripard]

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@cerno.tech/
> 
> 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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