linux-kernel - Re: [RFC PATCH] led: add Cycle LED trigger.

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Date:	Thu, 20 Jun 2013 10:58:52 -0700
From:	Bryan Wu <cooloney@...il.com>
To:	Gaël PORTAY <g.portay@...rkiz.com>
Cc:	Joe Perches <joe@...ches.com>, Rob Landley <rob@...dley.net>,
	Richard Purdie <rpurdie@...ys.net>,
	"Milo(Woogyom) Kim" <milo.kim@...com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Linux LED Subsystem <linux-leds@...r.kernel.org>
Subject: Re: [RFC PATCH] led: add Cycle LED trigger.

On Thu, Jun 20, 2013 at 2:44 AM, Gaël PORTAY <g.portay@...rkiz.com> wrote:
> On 19/06/2013 00:05, Joe Perches wrote:
>>
>> On Tue, 2013-06-18 at 18:24 +0200, Gaël PORTAY wrote:
>>>
>>> Currently, none of available triggers supports playing with the LED
>>> brightness
>>> level.  The cycle trigger provides a way to define custom brightness
>>> cycle.
>>> For example, it is easy to customize the cycle to mock up the rhythm of
>>> human
>>> breathing which is a nice cycle to tell the user the system is doing
>>> something.
>>
>> I think maybe this is a userspace thing, but here's a
>> trivial comment or two
>>
>>
>>> +static int cycle_start(struct cycle_trig_data *data)
>>> +{
>>> +       unsigned long flags;
>>> +
>>> +       if (hrtimer_active(&data->timer))
>>> +               return -EINVAL;
>>> +
>>> +       spin_lock_irqsave(&data->lock, flags);
>>> +       data->plot_index = 0;
>>> +       data->cycle_count = 0;
>>> +       hrtimer_start(&data->timer, ktime_get(), HRTIMER_MODE_ABS);
>>> +       spin_unlock_irqrestore(&data->lock, flags);
>>> +
>>> +       return 1;
>>
>> Maybe return 0 on success
>>
>>> +static ssize_t cycle_control_store(struct device *dev,
>>> +                                   struct device_attribute *attr,
>>> +                                   const char *buf, size_t size)
>>> +{
>>> +       struct led_classdev *led_cdev = dev_get_drvdata(dev);
>>> +       struct cycle_trig_data *data = led_cdev->trigger_data;
>>> +
>>> +       if (strncmp(buf, "start", sizeof("start") - 1) == 0)
>>> +               cycle_start(data);
>>> +       else if (strncmp(buf, "stop", sizeof("stop") - 1) == 0)
>>> +               cycle_stop(data);
>>> +       else if (strncmp(buf, "reset", sizeof("reset") - 1) == 0)
>>> +               cycle_reset(data);
>>> +       else if (strncmp(buf, "pause", sizeof("stop") - 1) == 0)
>>> +               cycle_pause(data);
>>> +       else if (strncmp(buf, "resume", sizeof("resume") - 1) == 0)
>>> +               cycle_resume(data);
>>> +       else
>>> +               return -EINVAL;
>>
>> I think strcasecmp better than strncmp
>>
>>> +static ssize_t cycle_rawplot_store(struct device *dev,
>>> +                                  struct device_attribute *attr,
>>> +                                  const char *buf, size_t size)
>>> +{
>>
>> []
>> +       plot = kzalloc(size, GFP_KERNEL);
>> +       if (plot) {
>> +               hrtimer_cancel(&data->timer);
>>
>> Ick.
>>
>>         if (!plot)
>>                 return -ENOMEM;
>>
>>         etc...
>>
> Hello,
>
> Thanks a lot for your review. I took your remarks into consideration and
> fixed the mistakes.
>
> About the kernel/user space discussion, I'd rather keep the cycle trigger
> implementation in the kernel space,
> because it implies brightness change every 10-100ms or less. This leads to
> lots of context switches, and I'm not
> even sure the user space can handle such timings accurately.
>
> Could you detail your concerns about adding this driver in the kernel?
>
> Best Regards,
> Gaël

Hi Gaël,

Is that possible to extend an existing leds trigger like ledtrig-timer
or other triggers instead of creating a new one?

Thanks,
-Bryan
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