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

Baolin Wang
2018-08-06T11:43:29Z

Hi Jacek,

On 6 August 2018 at 19:41, Jacek Anaszewski <jacek.anaszewski@gmail.com> wrote:
> 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.

Sure. Thanks.

>
> [...]
>>>> +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

--
Baolin Wang
Best Regards