linux-kernel - Re: [PATCH 1/2] leds: core: Introduce generic pattern interface

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Date:   Mon, 25 Jun 2018 14:18:45 +0200
From:   Pavel Machek <pavel@....cz>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     jacek.anaszewski@...il.com, bjorn.andersson@...aro.org,
        broonie@...nel.org, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] leds: core: Introduce generic pattern interface

On Mon 2018-06-25 13:03:19, Baolin Wang wrote:
> From: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> Some LED controllers have support for autonomously controlling
> brightness over time, according to some preprogrammed pattern or
> function.
> 
> This adds a new optional operator that LED class drivers can implement
> if they support such functionality as well as a new device attribute to
> configure the pattern for a given LED.

Thanks for doing this!

> index 5f67f7a..fe90a12 100644
> --- a/Documentation/ABI/testing/sysfs-class-led
> +++ b/Documentation/ABI/testing/sysfs-class-led
> @@ -61,3 +61,19 @@ Description:
>  		gpio and backlight triggers. In case of the backlight trigger,
>  		it is useful when driving a LED which is intended to indicate
>  		a device in a standby like state.
> +
> +What: /sys/class/leds/<led>/pattern
> +Date: June 2018
> +KernelVersion: 4.18
> +Description:
> +	Specify a pattern for the LED, for LED hardware that support
> +	altering the brightness as a function of time.
> +
> +	The pattern is given by a series of tuples, of brightness and
> +	duration (ms). The LED is expected to traverse the series and
> +	each brightness value for the specified duration.
> +
> +	As LED hardware might have different capabilities and precision
> +	the requested pattern might be slighly adjusted by the driver
> +	and the resulting pattern of such operation should be returned
> +	when this file is read.

I'd add "Duration of 0 means brightness should immediately change to
new value."

> +	struct led_classdev *led_cdev = dev_get_drvdata(dev);
> +	struct led_pattern *pattern = NULL;
> +	unsigned long val;
> +	char *sbegin;
> +	char *elem;
> +	char *s;
> +	int ret, len = 0;
> +	bool odd = true;
> +
> +	s = sbegin = kstrndup(buf, size, GFP_KERNEL);
> +	if (!s)
> +		return -ENOMEM;
> +
> +	/* Trim trailing newline */
> +	s[strcspn(s, "\n")] = '\0';

Is substring function best to use here? Will it do the right thing
when \n is not present?

> +	/* If the remaining string is empty, clear the pattern */
> +	if (!s[0]) {
> +		ret = led_cdev->pattern_clear(led_cdev);
> +		goto out;
> +	}
> +
> +	pattern = kcalloc(size, sizeof(*pattern), GFP_KERNEL);
> +	if (!pattern) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	/* Parse out the brightness & delta_t touples and check for repeat */
> +	while ((elem = strsep(&s, " ")) != NULL) {
> +		ret = kstrtoul(elem, 10, &val);
> +		if (ret)
> +			goto out;
> +
> +		if (odd) {
> +			pattern[len].brightness = val;
> +		} else {
> +			/* Ensure we don't have any delta_t == 0 */
> +			if (!val) {
> +				ret = -EINVAL;
> +				goto out;
> +			}

I believe we should support delta_t of 0 for "change immediately".

Thanks,
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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