Re: [PATCH V3 2/2] pwm: Add GPIO PWM driver

[Stefan Wahren <wahrenst@gmx.net>]

Hi Sean,

Am 30.01.24 um 10:08 schrieb Sean Young:
> On Sun, Jan 28, 2024 at 05:36:30PM +0100, Stefan Wahren 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.
>>
>> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
>> Co-developed-by: Stefan Wahren <wahrenst@gmx.net>
>> Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
>> ---
...
>> +
>> +static int pwm_gpio_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>> +			  const struct pwm_state *state)
>> +{
>> +	struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip);
>> +	bool invert = state->polarity == PWM_POLARITY_INVERSED;
>> +	unsigned long flags;
> Not sure this is necessary but how about:
>
> 	if (state->duty_cycle < hrtimer_resolution ||
> 	    state->period - state->duty_cycle < hrtimer_resolution)
> 		return -EINVAL;
>
i think i get the idea, but we need to care about corner cases like
duty_cycle = 0