Add a software PWM which toggles a GPIO from a high-resolution timer. Recent discussions in the Raspberry Pi community revealt that a lot of users still use MMIO userspace tools for GPIO access. One argument for this approach is the lack of a GPIO PWM kernel driver. So this series tries to fill this gap. This continues the work of Vincent Whitchurch [1], which is easier to read and more consequent by rejecting sleeping GPIOs than Nicola's approach [2]. The latest version has just been boot tested on a Raspberry Pi 3 B+. Since i'm not sure that i have the time to finish the driver soon, i'm happy if someone finish this job. From my POV, V5 of this series only lacks a solution for possible interrupt storm in case the period/duty cycle is set too short [3]. V5: - add Reviewed-by's for dt-binding patch - rebase on top of v6.10-rc1 - print hr resolution at driver probe - fix grammar in Kconfig - fix return type of pwm_gpio_toggle - implement hrtimer resolution rounding as noted by Uwe - use firmware node path instead of GPIO numbers as suggested by Andy - adjust some header includes and style issues as noted by Andy V4: - address DT bindings comments from Conor Dooley - drop unnecessary MODULE_ALIAS() as suggested by Krzysztof Kozlowski - add range checks to apply which consider the hrtimer resolution (idea comes from Sean Young) - mark driver as atomic as suggested by Sean Young V3: - rebase on top of v6.8-pwm-next - cherry-pick improvements from Nicola's series - try to address Uwe's, Linus' and Andy's comments - try to avoid GPIO glitches during probe - fix pwm_gpio_remove() - some code clean up's and comments V2: - Rename gpio to gpios in binding - Calculate next expiry from expected current expiry rather than "now" - Only change configuration after current period ends - Implement get_state() - Add error message for probe failures - Stop PWM before unregister [1] - https://lore.kernel.org/all/20200915135445.al75xmjxudj2rgcp@xxxxxxxx/T/ [2] - https://lore.kernel.org/all/20201205214353.xapax46tt5snzd2v@xxxxxxxxxxxxxxxxxxx/ [3] - https://lore.kernel.org/linux-pwm/CACRpkdary+kDrTJ=u4VbSTv7wXGLQj9_fy7mv0w-Zg+eDvGXVQ@xxxxxxxxxxxxxx/T/#m513f255daa9f30c325d11999cacd086411591bf9 Nicola Di Lieto (1): dt-bindings: pwm: Add pwm-gpio Vincent Whitchurch (1): pwm: Add GPIO PWM driver .../devicetree/bindings/pwm/pwm-gpio.yaml | 42 +++ drivers/pwm/Kconfig | 11 + drivers/pwm/Makefile | 1 + drivers/pwm/pwm-gpio.c | 249 ++++++++++++++++++ 4 files changed, 303 insertions(+) create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.yaml create mode 100644 drivers/pwm/pwm-gpio.c -- 2.34.1
