| Message ID | 20240602-pwm-gpio-v6-0-e8f6ec9cc783@linaro.org |
|---|---|
| Headers | show |
| Series | pwm: Add GPIO PWM driver | expand |
On Sun, Jun 2, 2024 at 11:33 PM Linus Walleij <linus.walleij@linaro.org> wrote: > > From: Vincent Whitchurch <vincent.whitchurch@axis.com> > > Add a software PWM which toggles a GPIO from a high-resolution timer. > > This will naturally not be as accurate or as efficient as a hardware > PWM, but it is useful in some cases. I have for example used it for > evaluating LED brightness handling (via leds-pwm) on a board where the > LED was just hooked up to a GPIO, and for a simple verification of the > timer frequency on another platform. > > Since high-resolution timers are used, sleeping GPIO chips are not > supported and are rejected in the probe function. Reviewed-by: Andy Shevchenko <andy@kernel.org> See one question below. ... > +static int pwm_gpio_probe(struct platform_device *pdev) > +{ > + struct device *dev = &pdev->dev; > + struct pwm_chip *chip; > + struct pwm_gpio *gpwm; > + int ret; > + > + chip = devm_pwmchip_alloc(dev, 1, sizeof(*gpwm)); > + if (IS_ERR(chip)) > + return PTR_ERR(chip); > + > + gpwm = pwmchip_get_drvdata(chip); > + > + spin_lock_init(&gpwm->lock); > + > + gpwm->gpio = devm_gpiod_get(dev, NULL, GPIOD_ASIS); > + if (IS_ERR(gpwm->gpio)) > + return dev_err_probe(dev, PTR_ERR(gpwm->gpio), > + "%pfw: could not get gpio\n", > + dev_fwnode(dev)); > + > + if (gpiod_cansleep(gpwm->gpio)) > + return dev_err_probe(dev, -EINVAL, > + "%pfw: sleeping GPIO not supported\n", > + dev_fwnode(dev)); > + > + chip->ops = &pwm_gpio_ops; > + chip->atomic = true; > + > + hrtimer_init(&gpwm->gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); > + ret = devm_add_action_or_reset(dev, pwm_gpio_disable_hrtimer, gpwm); > + if (ret) > + return ret; > + > + gpwm->gpio_timer.function = pwm_gpio_timer; > + > + ret = pwmchip_add(chip); > + if (ret < 0) > + return dev_err_probe(dev, ret, "could not add pwmchip\n"); > + platform_set_drvdata(pdev, gpwm); Do we still need this? > + return 0; > +}
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]. It further takes over where Stefan Wahren left off. I have not looked into the interrupt storm problem mentioned in [3] but instead focused on some real-life tests: The IXP4xx NSLU2 has a speaker connected directly to a GPIO, and I wanted to use this patch to provide a proper beeper for the machine and not have to rely on custom hacks. I added a DTS patch like this: gpio_pwm: pwm { #pwm-cells = <3>; compatible = "pwm-gpio"; gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>; }; beeper { compatible = "pwm-beeper"; pwms = <&gpio_pwm 0 1 0>; beeper-hz = <1000>; }; Then activated the necessary drivers with input evdev and they both probe fine. Then I use this test program: https://gist.github.com/licheegh/3dbdc8918325e8af8d4d13805cd0c350 with a few different beep frequencies, such as "beep 400" for an OK sounding 400 Hz signal. Above ~10000 Hz the sound becomes bad and mostly sound like different kinds of noise. But this is not so bad for the NSLU2 which is a 266 MHz ARM XScale machine, and we do not need any better on this machine so mission accomplished. Pushing the playback to higher and higher rates does not crash the machine, the sample program always terminates. Signed-off-by: Linus Walleij <linus.walleij@linaro.org> --- v6: - Add a small blurb to drivers-on-gpio.rst - Add missing headers to driver - Use guarded spinlocks from <linux/cleanup.h> - Drop minor surplus whitespace - Use dev pointer everywhere in probe() - Drop dev_info() chatter at end of probe() - Use devm_add_action_or_reset() for a hook to disable the hrtimer and get rid of the .remove() callback altogether. 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@axis.com/T/ [2] - https://lore.kernel.org/all/20201205214353.xapax46tt5snzd2v@einstein.dilieto.eu/ [3] - https://lore.kernel.org/linux-pwm/CACRpkdary+kDrTJ=u4VbSTv7wXGLQj9_fy7mv0w-Zg+eDvGXVQ@mail.gmail.com/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 ++++ Documentation/driver-api/gpio/drivers-on-gpio.rst | 7 +- drivers/pwm/Kconfig | 11 + drivers/pwm/Makefile | 1 + drivers/pwm/pwm-gpio.c | 243 +++++++++++++++++++++ 5 files changed, 303 insertions(+), 1 deletion(-) --- base-commit: cc97b8f37b097a1598410154ca472964a1d9b255 change-id: 20240530-pwm-gpio-e9133a1806ec Best regards,