linux-kernel - Re: [PATCH v4 1/3] led: make led_set_brightness_sync() use led_set_brightness

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Date:   Mon, 23 Sep 2019 11:14:20 +0200
From:   Jean-Jacques Hiblot <jjhiblot@...com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>, <pavel@....cz>,
        <daniel.thompson@...aro.org>
CC:     <linux-leds@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dmurphy@...com>, <tomi.valkeinen@...com>
Subject: Re: [PATCH v4 1/3] led: make led_set_brightness_sync() use
 led_set_brightness_nosleep()

Hi Jacek,

On 20/09/2019 23:10, Jacek Anaszewski wrote:
> Hi Jean,
>
> On 9/20/19 2:25 PM, Jean-Jacques Hiblot wrote:
>> Making led_set_brightness_sync() use led_set_brightness_nosleep() has 2
>> advantages:
>> - works for LED controllers that do not provide brightness_set_blocking()
>> - When the blocking callback is used, it uses the workqueue to update the
>>    LED state, removing the need for mutual exclusion between
>>    led_set_brightness_sync() and set_brightness_delayed().
> And third:
>
> - it compromises the "sync" part of the function name :-)

Making it sync is the role of the flush_work() function. It waits until 
the deferred work has been done.

JJ

> This function has been introduced specifically to be blocking
> and have the immediate effect. Its sole client is
> drivers/media/v4l2-core/v4l2-flash-led-class.c.
>
>> Signed-off-by: Jean-Jacques Hiblot <jjhiblot@...com>
>> ---
>>   drivers/leds/led-core.c | 12 +++++++-----
>>   1 file changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
>> index f1f718dbe0f8..50e28a8f9357 100644
>> --- a/drivers/leds/led-core.c
>> +++ b/drivers/leds/led-core.c
>> @@ -294,15 +294,17 @@ EXPORT_SYMBOL_GPL(led_set_brightness_nosleep);
>>   int led_set_brightness_sync(struct led_classdev *led_cdev,
>>   			    enum led_brightness value)
>>   {
>> +	int ret;
>> +
>>   	if (led_cdev->blink_delay_on || led_cdev->blink_delay_off)
>>   		return -EBUSY;
>>   
>> -	led_cdev->brightness = min(value, led_cdev->max_brightness);
>> -
>> -	if (led_cdev->flags & LED_SUSPENDED)
>> -		return 0;
>> +	ret = led_set_brightness_nosleep(led_cdev, value);
>> +	if (!ret)
>> +		return ret;
>>   
>> -	return __led_set_brightness_blocking(led_cdev, led_cdev->brightness);
>> +	flush_work(&led_cdev->set_brightness_work);
>> +	return 0;
>>   }
>>   EXPORT_SYMBOL_GPL(led_set_brightness_sync);
>>   
>>