linux-kernel - Re: [PATCH 3/3] led: ledtrig-transient: add support for hrtimer

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Date:   Mon, 8 May 2017 22:25:00 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     David Lin <dtwlin@...gle.com>, corbet@....net, rpurdie@...ys.net,
        pavel@....cz, hdegoede@...hat.com, mark.rutland@....com,
        tony.makkiel@...ri.com, linz@...pro.net
Cc:     robh@...nel.org, romlem@...gle.com, joelaf@...gle.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH 3/3] led: ledtrig-transient: add support for hrtimer

Hi David,

Thanks for the patch. I have one reservation below.

On 04/30/2017 11:37 PM, David Lin wrote:
> This patch adds a hrtimer to ledtrig-transient so that when driver is
> registered with LED_BRIGHTNESS_FAST, the hrtimer is used for the better
> time accuracy in handling the duration.
> 
> Signed-off-by: David Lin <dtwlin@...gle.com>
> ---
>  drivers/leds/trigger/ledtrig-transient.c | 59 +++++++++++++++++++++++++++++---
>  1 file changed, 54 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/leds/trigger/ledtrig-transient.c b/drivers/leds/trigger/ledtrig-transient.c
> index 7e6011bd3646..63be54772596 100644
> --- a/drivers/leds/trigger/ledtrig-transient.c
> +++ b/drivers/leds/trigger/ledtrig-transient.c
> @@ -24,15 +24,18 @@
>  #include <linux/device.h>
>  #include <linux/slab.h>
>  #include <linux/timer.h>
> +#include <linux/hrtimer.h>
>  #include <linux/leds.h>
>  #include "../leds.h"
>  
>  struct transient_trig_data {
> +	struct led_classdev *led_cdev;
>  	int activate;
>  	int state;
>  	int restore_state;
>  	unsigned long duration;
>  	struct timer_list timer;
> +	struct hrtimer hrtimer;
>  };
>  
>  static void transient_timer_function(unsigned long data)
> @@ -44,6 +47,54 @@ static void transient_timer_function(unsigned long data)
>  	led_set_brightness_nosleep(led_cdev, transient_data->restore_state);
>  }
>  
> +static enum hrtimer_restart transient_hrtimer_function(struct hrtimer *timer)
> +{
> +	struct transient_trig_data *transient_data =
> +		container_of(timer, struct transient_trig_data, hrtimer);
> +
> +	transient_timer_function((unsigned long)transient_data->led_cdev);
> +
> +	return HRTIMER_NORESTART;
> +}
> +
> +static inline void transient_timer_setup(struct led_classdev *led_cdev)
> +{
> +	struct transient_trig_data *tdata = led_cdev->trigger_data;
> +
> +	if (led_cdev->flags & LED_BRIGHTNESS_FAST) {
> +		tdata->led_cdev = led_cdev;
> +		hrtimer_init(&tdata->hrtimer, CLOCK_MONOTONIC,
> +			     HRTIMER_MODE_REL);
> +		tdata->hrtimer.function = transient_hrtimer_function;
> +	} else {
> +		setup_timer(&tdata->timer, transient_timer_function,
> +			    (unsigned long)led_cdev);
> +	}
> +}
> +
> +static inline void transient_timer_start(struct led_classdev *led_cdev)
> +{
> +	struct transient_trig_data *tdata = led_cdev->trigger_data;
> +
> +	if (led_cdev->flags & LED_BRIGHTNESS_FAST) {
> +		hrtimer_start(&tdata->hrtimer, ms_to_ktime(tdata->duration),
> +			      HRTIMER_MODE_REL);
> +	} else {
> +		mod_timer(&tdata->timer,
> +			  jiffies + msecs_to_jiffies(tdata->duration));
> +	}
> +}
> +
> +static inline void transient_timer_cancel(struct led_classdev *led_cdev)
> +{
> +	struct transient_trig_data *tdata = led_cdev->trigger_data;
> +
> +	if (led_cdev->flags & LED_BRIGHTNESS_FAST)
> +		hrtimer_cancel(&tdata->hrtimer);
> +	else
> +		del_timer_sync(&tdata->timer);
> +}

These functions don't seem to be good candidates for marking them with
inline modifier due to below reasons:

- they have more than three lines of code
- their parameters are not compiletime constants
- the functions are static and used only once - in this case
  gcc is capable of inlining them automatically without help

This is concise excerpt from the Documentation/process/coding-style.rst,
chapter 15.

>  static ssize_t transient_activate_show(struct device *dev,
>  		struct device_attribute *attr, char *buf)
>  {
> @@ -70,7 +121,7 @@ static ssize_t transient_activate_store(struct device *dev,
>  
>  	/* cancel the running timer */
>  	if (state == 0 && transient_data->activate == 1) {
> -		del_timer(&transient_data->timer);
> +		transient_timer_cancel(led_cdev);
>  		transient_data->activate = state;
>  		led_set_brightness_nosleep(led_cdev,
>  					transient_data->restore_state);
> @@ -84,8 +135,7 @@ static ssize_t transient_activate_store(struct device *dev,
>  		led_set_brightness_nosleep(led_cdev, transient_data->state);
>  		transient_data->restore_state =
>  		    (transient_data->state == LED_FULL) ? LED_OFF : LED_FULL;
> -		mod_timer(&transient_data->timer,
> -			  jiffies + msecs_to_jiffies(transient_data->duration));
> +		transient_timer_start(led_cdev);
>  	}
>  
>  	/* state == 0 && transient_data->activate == 0
> @@ -182,8 +232,7 @@ static void transient_trig_activate(struct led_classdev *led_cdev)
>  	if (rc)
>  		goto err_out_state;
>  
> -	setup_timer(&tdata->timer, transient_timer_function,
> -		    (unsigned long) led_cdev);
> +	transient_timer_setup(led_cdev);
>  	led_cdev->activated = true;
>  
>  	return;
> 

-- 
Best regards,
Jacek Anaszewski