Re: [PATCH v4 1/2] leds: core: Introduce LED pattern trigger

Jacek Anaszewski
2018-08-06T11:41:37Z

Hi Baolin,

On 08/06/2018 03:53 AM, Baolin Wang wrote:
> Hi Jacek,
[...]
>>> +++ b/Documentation/ABI/testing/sysfs-class-led-trigger-pattern
>>> @@ -0,0 +1,21 @@
>>> +What: /sys/class/leds/<led>/pattern
>>> +Date: August 2018
>>> +KernelVersion: 4.19
>>> +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. Duration of
>>> + 0 means brightness should immediately change to new value.
>>> +
>>> + The format of the pattern values should be:
>>> + "brightness_1 duration_1 brightness_2 duration_2 brightness_3
>>> + duration_3 ...".
>>> +
>>> +What: /sys/class/leds/<led>/repeat
>>> +Date: August 2018
>>> +KernelVersion: 4.19
>>> +Description:
>>> + Specify a pattern repeat number. 0 means repeat indefinitely.
>>
>> In current implementation this file on read returns the number
>> of remaining repeat intervals. I'd add that to this description.
>
> I saw Pavel's comments that he did not suggest do this. So I will keep
> the original description?

Yes, please report always the original value.

[...]
>>> +static ssize_t pattern_trig_store_repeat(struct device *dev,
>>> + struct device_attribute *attr,
>>> + const char *buf, size_t count)
>>> +{
>>> + struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>> + struct pattern_trig_data *data = led_cdev->trigger_data;
>>> + unsigned long res;
>>> + int err;
>>> +
>>> + err = kstrtoul(buf, 10, &res);
>>> + if (err)
>>> + return err;
>>> +
>>> + if (!led_cdev->pattern_set)
>>> + del_timer_sync(&data->timer);
>>
>> Is there a reason for not having this check under mutex?
>
> We will hold the mutex in pattern_trig_timer_function(), so if we do
> del_timer_sync() under the mutex protection, we may meet dead-lock
> issue. Moreover, the del_timer_sync() will make sure deactivating one
> timer is safe.

Ack.

--
Best regards,
Jacek Anaszewski