linux-kernel - Re: [PATCH 1/2] pwm: Add different PWM output types support

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Message-ID: <20190916182524.5ebby6pbsbkuahci@pengutronix.de>
Date:   Mon, 16 Sep 2019 20:25:24 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Guru Das Srinagesh <gurus@...eaurora.org>
Cc:     linux-pwm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        kernel-team@...roid.com, Mark Salyzyn <salyzyn@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Subbaraman Narayanamurthy <subbaram@...eaurora.org>,
        linux-kernel@...r.kernel.org, Fenglin Wu <fenglinw@...eaurora.org>
Subject: Re: [PATCH 1/2] pwm: Add different PWM output types support

Hello,

On Fri, Sep 13, 2019 at 03:57:43PM -0700, Guru Das Srinagesh wrote:
> From: Fenglin Wu <fenglinw@...eaurora.org>
> 
> Normally, PWM channel has fixed output until software request to change
> its settings. There are some PWM devices which their outputs could be
> changed autonomously according to a predefined pattern programmed in
> hardware. Add pwm_output_type enum type to identify these two different
> PWM types and add relevant helper functions to set and get PWM output
> types and pattern.

I have problems to understand what your modulated mode does even after
reading your commit log and the patch.

Also you should note here what is the intended usage and add support for
it for at least one (preferably more) drivers to make this actually
usable.

> Change-Id: Ia1f914a45ab4f4dd7be037a395eeb89d0e65a80e

In Linux we don't use these. You're making it easier to apply your patch
if you drop the change-id lines.

> diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c
> index 2389b86..ab703f2 100644
> --- a/drivers/pwm/sysfs.c
> +++ b/drivers/pwm/sysfs.c
> @@ -215,11 +215,60 @@ static ssize_t capture_show(struct device *child,
>  	return sprintf(buf, "%u %u\n", result.period, result.duty_cycle);
>  }
>  
> +static ssize_t output_type_show(struct device *child,
> +			     struct device_attribute *attr,
> +			     char *buf)
> +{
> +	const struct pwm_device *pwm = child_to_pwm_device(child);
> +	const char *output_type = "unknown";
> +	struct pwm_state state;
> +
> +	pwm_get_state(pwm, &state);
> +	switch (state.output_type) {
> +	case PWM_OUTPUT_FIXED:
> +		output_type = "fixed";
> +		break;
> +	case PWM_OUTPUT_MODULATED:
> +		output_type = "modulated";
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	return snprintf(buf, PAGE_SIZE, "%s\n", output_type);
> +}
> +
> +static ssize_t output_type_store(struct device *child,
> +			      struct device_attribute *attr,
> +			      const char *buf, size_t size)
> +{
> +	struct pwm_export *export = child_to_pwm_export(child);
> +	struct pwm_device *pwm = export->pwm;
> +	struct pwm_state state;
> +	int ret = -EINVAL;
> +
> +	mutex_lock(&export->lock);
> +	pwm_get_state(pwm, &state);
> +	if (sysfs_streq(buf, "fixed"))
> +		state.output_type = PWM_OUTPUT_FIXED;
> +	else if (sysfs_streq(buf, "modulated"))
> +		state.output_type = PWM_OUTPUT_MODULATED;
> +	else
> +		goto unlock;
> +
> +	ret = pwm_apply_state(pwm, &state);
> +unlock:
> +	mutex_unlock(&export->lock);
> +
> +	return ret ? : size;
> +}

So in sysfs you cannot set a pattern. Doesn't that mean this makes using
modulated mode hardly useful?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
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