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

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Date:   Mon, 6 Aug 2018 19:43:25 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Pavel Machek <pavel@....cz>, rteysseyre@...il.com,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/2] leds: core: Introduce LED pattern trigger

Hi Jacek,

On 6 August 2018 at 19:41, Jacek Anaszewski <jacek.anaszewski@...il.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