The fractional divider approximation does not utilize the full available
range for clocks that are flagged CLK_FRAC_DIVIDER_ZERO_BASED. This
patchset aims to fix that.

It also adds test cases for the edge cases of fractional divider clocks
with and without the CLK_FRAC_DIVIDER_ZERO_BASED flag to highlight the
changes.

Finally, it also exports clk_fractional_divider_general_approximation so
that the test cases (but also other users like rockchip clk driver) can
be compiled as a module.

Unfortunately, I have no boards to test this patch. So all we have are
the unit tests. It seems the only user of this flag in mainline is
drivers/clk/imx/clk-composite-7ulp.c, therefore I'm cc-ing
get_maintainers.pl --git-blame -f drivers/clk/imx/clk-composite-7ulp.c
in the hopes of a wider audience.

Thank you for considering this contribution,
  Frank

P.S.: V4 was short-lived, because it triggered a compiler warning on
clang. I'm sorry for the noise. -- Frank

V4: https://lore.kernel.org/all/20230617102919.27564-1-frank@oltmanns.dev/ (local)
V3: https://lore.kernel.org/all/20230614185521.477924-1-frank@oltmanns.dev/ (local)
V2: https://lore.kernel.org/lkml/20230613083626.227476-1-frank@oltmanns.dev/ (local)
V1: https://lore.kernel.org/lkml/20230529133433.56215-1-frank@oltmanns.dev/ (local)

Changes in V5 (since V4):
 - Fix compiler warnings on clang by removing superfluous variable max_m
   in the test cases for the maximum denominator (n) and max_n in the
   test cases for max numerator (m).
   Thank you, Intel, for your kernel test robot!

Changes in V4 (since V3):
 - Export clk_fractional_divider_general_approximation so that users
   (e.g., the testcases) can be compiled as modules.
 - Change test cases so that they test
   clk_fractional_divider_general_approximation again (like in V2)
   instead of clk_fd_round_rate (like in V3), but keeping the structure
   of V3 with separate file and individual test cases for each edge
   case.

Changes in V3 (since V2):
 - Completely reworked the test cases
   - Moved tests to separate file as per Stephen's request
   - Move each edge case into their individual test case as per
     Stephen's request
   - Test clk_fd_round_rate instead of
     clk_fractional_divider_general_approximation as testing the latter
     broke builds

Changes in V2 (since V1):
 - Added test case as requested by Stephen Boyd
 - Fixed commit message as the Cc: was missing a closing bracket, so that the
   original mail unfortunately did not go out to A. s. Dong.

Frank Oltmanns (2):
  clk: fractional-divider: Improve approximation when zero based and
    export
  clk: fractional-divider: tests: Add test suite for edge cases

 drivers/clk/.kunitconfig                  |   1 +
 drivers/clk/Kconfig                       |   7 +
 drivers/clk/Makefile                      |   1 +
 drivers/clk/clk-fractional-divider.c      |  27 +++-
 drivers/clk/clk-fractional-divider_test.c | 157 ++++++++++++++++++++++
 5 files changed, 186 insertions(+), 7 deletions(-)
 create mode 100644 drivers/clk/clk-fractional-divider_test.c

-- 
2.41.0


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