Subject: [PATCH v2 0/3] pwm: rockchip: Eliminate potential race condition when probing

From: Simon South <[email-masked]>
Date: Sat, 19 Dec 2020 15:44:07 -0500

This patch series aims to eliminate the race condition Trent Piepho
identified[0] in the Rockchip PWM driver's rockchip_pwm_probe()
function, by moving code that disables a PWM device's signal clock
ahead of the code that registers the device via pwmchip_add().

It additionally

- Fixes a potential kernel hang introduced by my earlier commit
  457f74abbed0 ("pwm: rockchip: Keep enabled PWMs running while
  probing") by ensuring a device's APB clock is enabled before its
  registers are accessed, and

- Tries to improve the driver by (re-)enabling the signal clock of
  only PWM devices that appear to have been started already by the
  bootloader, rather than enabling every device's signal clock and
  selectively disabling it later.

I've tested these changes on my (RK3399-based) Pinebook Pro with its
screen backlight enabled by U-Boot and they appear to work fine.

I'd be grateful for help with testing on other devices, particularly
those with SoCs like the RK3328 that use separate bus and signal
clocks for their PWM devices. (My ROCK64 uses its PWM-output pins for
other purposes and wasn't of help here.)

[0] https://www.spinics.net/lists/linux-pwm/msg14611.html

--
Simon South
[email-masked]

Simon South (3):
  pwm: rockchip: Enable APB clock during register access while probing
  pwm: rockchip: Eliminate potential race condition when probing
  pwm: rockchip: Do not start PWMs not already running

 drivers/pwm/pwm-rockchip.c | 49 +++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 25 deletions(-)

-- 
2.29.2

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