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

[Gaël PORTAY]

On Jun 20, 2013, at 7:58 PM, Bryan Wu <cooloney@xxxxxxxxx> wrote:

> On Thu, Jun 20, 2013 at 2:44 AM, Gaël PORTAY <g.portay@xxxxxxxxxxx> 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

Hi Bryan,

I'm sorry but the cycle trigger interface is too much different from 
already defined triggers. That's why I have decided to create a new one.

The cycle trigger purposes are:
 - to control a cycle (start/stop pause/resume reset), and
 - to play with the brightness level

But it's possible to implement the timer and heartbeat triggers using 
the interface of the cycle trigger.

Yours sincerely,
Gaël


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