linux-kernel - Re: [PATCH v6] staging: greybus: introduce pwm

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Message-ID: <a4b3ad02-f1c7-c13b-7740-d5b9982bd7c7@linaro.org>
Date:   Fri, 18 Mar 2022 07:15:34 -0500
From:   Alex Elder <elder@...aro.org>
To:     Song Chen <chensong_2000@....cn>, johan@...nel.org,
        elder@...nel.org, gregkh@...uxfoundation.org,
        thierry.reding@...il.com, u.kleine-koenig@...gutronix.de,
        lee.jones@...aro.org, greybus-dev@...ts.linaro.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, elder@...e.org
Subject: Re: [PATCH v6] staging: greybus: introduce pwm_ops::apply

On 3/18/22 4:57 AM, Song Chen wrote:
> Introduce newer .apply function in pwm_ops to replace legacy operations
> including enable, disable, config and set_polarity.
> 
> This guarantees atomic changes of the pwm controller configuration.
> 
> Signed-off-by: Song Chen <chensong_2000@....cn>

I had another comment suggestion but you've been through enough.
Thanks for working this to completion.

Reviewed-by: Alex Elder <elder@...aro.org>

> 
> ---
> v2:
> 1, define duty_cycle and period as u64 in gb_pwm_config_operation.
> 2, define duty and period as u64 in gb_pwm_config_request.
> 3, disable before configuring duty and period if the eventual goal
>     is a disabled state.
> 
> v3:
> Regarding duty_cycle and period, I read more discussion in this thread,
> min, warn or -EINVAL, seems no perfect way acceptable for everyone.
> How about we limit their value to INT_MAX and throw a warning at the
> same time when they are wrong?
> 
> v4:
> 1, explain why legacy operations are replaced.
> 2, cap the value of period and duty to U32_MAX.
> 
> v5:
> 1, revise commit message.
> 
> v6:
> 1, revise commit message.
> 2, explain why capping the value of period and duty to U32_MAX in
>     comment.
> ---
>   drivers/staging/greybus/pwm.c | 64 ++++++++++++++++++++++-------------
>   1 file changed, 40 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/staging/greybus/pwm.c b/drivers/staging/greybus/pwm.c
> index 891a6a672378..ad20ec24031e 100644
> --- a/drivers/staging/greybus/pwm.c
> +++ b/drivers/staging/greybus/pwm.c
> @@ -204,43 +204,59 @@ static void gb_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm)
>   	gb_pwm_deactivate_operation(pwmc, pwm->hwpwm);
>   }
>   
> -static int gb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
> -			 int duty_ns, int period_ns)
> +static int gb_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			const struct pwm_state *state)
>   {
> +	int err;
> +	bool enabled = pwm->state.enabled;
> +	u64 period = state->period;
> +	u64 duty_cycle = state->duty_cycle;
>   	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
>   
> -	return gb_pwm_config_operation(pwmc, pwm->hwpwm, duty_ns, period_ns);
> -};
> +	/* Set polarity */
> +	if (state->polarity != pwm->state.polarity) {
> +		if (enabled) {
> +			gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> +			enabled = false;
> +		}
> +		err = gb_pwm_set_polarity_operation(pwmc, pwm->hwpwm, state->polarity);
> +		if (err)
> +			return err;
> +	}
>   
> -static int gb_pwm_set_polarity(struct pwm_chip *chip, struct pwm_device *pwm,
> -			       enum pwm_polarity polarity)
> -{
> -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> +	if (!state->enabled) {
> +		if (enabled)
> +			gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> +		return 0;
> +	}
>   
> -	return gb_pwm_set_polarity_operation(pwmc, pwm->hwpwm, polarity);
> -};
> +	/*
> +	 * Set period and duty cycle
> +	 *
> +	 * PWM privodes 64-bit period and duty_cycle, but greybus only accepts
> +	 * 32-bit, so their values have to be limited to U32_MAX.
> +	 */
> +	if (period > U32_MAX)
> +		period = U32_MAX;
>   
> -static int gb_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> -{
> -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> +	if (duty_cycle > period)
> +		duty_cycle = period;
>   
> -	return gb_pwm_enable_operation(pwmc, pwm->hwpwm);
> -};
> +	err = gb_pwm_config_operation(pwmc, pwm->hwpwm, duty_cycle, period);
> +	if (err)
> +		return err;
>   
> -static void gb_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
> -{
> -	struct gb_pwm_chip *pwmc = pwm_chip_to_gb_pwm_chip(chip);
> +	/* enable/disable */
> +	if (!enabled)
> +		return gb_pwm_enable_operation(pwmc, pwm->hwpwm);
>   
> -	gb_pwm_disable_operation(pwmc, pwm->hwpwm);
> -};
> +	return 0;
> +}
>   
>   static const struct pwm_ops gb_pwm_ops = {
>   	.request = gb_pwm_request,
>   	.free = gb_pwm_free,
> -	.config = gb_pwm_config,
> -	.set_polarity = gb_pwm_set_polarity,
> -	.enable = gb_pwm_enable,
> -	.disable = gb_pwm_disable,
> +	.apply = gb_pwm_apply,
>   	.owner = THIS_MODULE,
>   };
>