Microchip soft ip corePWM driver

From: Conor Dooley <conor.dooley@microchip.com>

Hey Uwe, all,

(~same cover as v5)

Added some extra patches so I have a cover letter this time.
You pointed out that I was overriding npwmcells in the driver and I
realised that the dt & binding were not correct so I have added two
simple patches to deal with that. The dts patch I will take in my tree
once the binding is applied.

For the maintainers entry, I mentioned before that I have several
changes in-flight for it. We are late~(ish)~ in the cycle so I doubt
you'll be applying this for v5.20, but in the off chance you do - I
would be happy to send it (with your Ack) alongside an i2c addition
that is "deferred". I rebased it ~today~ on top of an additional change
so it may not apply for you.

In your review of v3, you had a lot of comments about the period and
duty cycle calculations, so I have had another run at them. I converted
the period calculation to "search" from the bottom up for the suitable
prescale value. The duty cycle calculation has been fixed - the problem
was exactly what I suspected in my replies to your review. I had to block
the use of a 0xFF period_steps register value (which I think should be
covered by the updated comment and limitation #2).

Beyond that, I have rebased on -next and converted to the devm_ stuff
in probe that was recently added & dropped remove() - as requested.
I added locking to protect the period racing, changed the #defines and
switched to returning -EINVAL when the period is locked to a value
greater than that requested.

I'll take the dts change myself once the rest is merged.

Thanks,
Conor.

Changes from v6:
- Dropped an unused variable that I'd missed
- Actually check the return values of the mutex lock()s
- Re-rebased on -next for the MAINTAINERS patch (again...)

Changes from v5:
- switched to a mutex b/c we must sleep with the lock taken
- simplified the locking in apply() and added locking to get_state()
- reworked apply() as requested
- removed the loop in the period calculation (thanks Uwe!)
- add a copy of the enable registers in the driver to save on reads.
- remove the second (useless) write to sync_update
- added some missing rounding in get_state()
- couple other minor cleanups as requested in:
https://lore.kernel.org/linux-riscv/20220709160206.cw5luo...

Changes from v4:
- dropped some accidentally added files

Conor Dooley (4):
  dt-bindings: pwm: fix microchip corePWM's pwm-cells
  riscv: dts: fix the icicle's #pwm-cells
  pwm: add microchip soft ip corePWM driver
  MAINTAINERS: add pwm to PolarFire SoC entry

 .../bindings/pwm/microchip,corepwm.yaml       |   4 +-
 MAINTAINERS                                   |   1 +
 .../dts/microchip/mpfs-icicle-kit-fabric.dtsi |   2 +-
 drivers/pwm/Kconfig                           |  10 +
 drivers/pwm/Makefile                          |   1 +
 drivers/pwm/pwm-microchip-core.c              | 371 ++++++++++++++++++
 6 files changed, 387 insertions(+), 2 deletions(-)
 create mode 100644 drivers/pwm/pwm-microchip-core.c


base-commit: a3fd3ca134d9485a0f9a7bdcffd7f8bae27f79d3
-- 
2.37.1