[PATCH v3 00/10] clk: Improve clock range handling

[Maxime Ripard]

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.

Let me know what you think
Maxime

Changes from v2:
  - Rebased on current next
  - Rewrote the whole thing according to Stephen reviews
  - Implemented some kunit tests

Changes from v1:
  - Return NULL in clk_request_start if clk pointer is NULL
  - Test for clk_req pointer in clk_request_done
  - Add another user in vc4
  - Rebased on top of v5.15-rc1

Maxime Ripard (10):
  clk: Add Kunit tests for rate
  clk: Always clamp the rounded rate
  clk: Use clamp instead of open-coding our own
  clk: Always set the rate on clk_set_range_rate
  clk: Add clk_drop_range
  clk: bcm: rpi: Add variant structure
  clk: bcm: rpi: Set a default minimum rate
  clk: bcm: rpi: Run some clocks at the minimum rate allowed
  drm/vc4: Add logging and comments
  drm/vc4: hdmi: Remove clock rate initialization

 drivers/clk/Kconfig               |   7 +
 drivers/clk/Makefile              |   1 +
 drivers/clk/bcm/clk-raspberrypi.c | 125 ++++++-
 drivers/clk/clk-rate-test.c       | 603 ++++++++++++++++++++++++++++++
 drivers/clk/clk.c                 |  51 ++-
 drivers/gpu/drm/vc4/vc4_hdmi.c    |  13 -
 drivers/gpu/drm/vc4/vc4_kms.c     |  11 +
 include/linux/clk.h               |  11 +
 8 files changed, 767 insertions(+), 55 deletions(-)
 create mode 100644 drivers/clk/clk-rate-test.c

-- 
2.34.1