Date:	Tue, 10 Apr 2012 09:31:56 -0600
From:	Shuah Khan <shuahkhan@...il.com>
To:	Richard Purdie <richard.purdie@...uxfoundation.org>
Cc:	shuahkhan@...il.com, akpm@...ux-foundation.org, neilb@...e.de,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] LEDS-One-Shot-Timer-Trigger-implementation

On Tue, 2012-04-10 at 14:24 +0100, Richard Purdie wrote:
> On Sun, 2012-04-01 at 13:53 -0600, Shuah Khan wrote:
> > LED infrastructure lacks support for one shot timer trigger and activation.
> > The current support allows for setting two timers, one for specifying how
> > long a state to be on, and the second for how long the state to be off. For
> > example, delay_on value specifies the time period an LED should stay in on
> > state, followed by a delay_off value that specifies how long the LED should
> > stay in off state. The on and off cycle repeats until the trigger gets
> > deactivated. There is no provision for one time activation to implement
> > features that require an on or off state to be held just once and then stay
> > in the original state forever.
> > 
> > This feature will help implement vibrate functionality which requires one
> > time activation of vibrate mode without a continuous vibrate on/off cycles.
> > 
> > From 1ebe0fd67580da833f8f06fc3119445e9991100f Mon Sep 17 00:00:00 2001
> > From: Shuah Khan <shuahkhan@...il.com>
> > Date: Sat, 31 Mar 2012 21:56:07 -0600
> > Subject: [PATCH] LEDS-One-Shot-Timer-Trigger-implementation
> > 
> > Signed-off-by: Shuah Khan <shuahkhan@...il.com>
> > Reviewed-by: NeilBrown <neilb@...e.de>
> > Cc: Richard Purdie <rpurdie@...ux.intel.com>
> > ---
> >  Documentation/leds/leds-one-shot-timer.txt |   79 +++++++++++++++++++++
> >  drivers/leds/led-class.c                   |    4 +-
> >  drivers/leds/led-core.c                    |   26 ++++++-
> >  drivers/leds/leds.h                        |    2 +
> >  drivers/leds/ledtrig-timer.c               |  104 ++++++++++++++++++++--------
> >  5 files changed, 180 insertions(+), 35 deletions(-)
> >  create mode 100644 Documentation/leds/leds-one-shot-timer.txt
> > 
> > diff --git a/Documentation/leds/leds-one-shot-timer.txt b/Documentation/leds/leds-one-shot-timer.txt
> > new file mode 100644
> > index 0000000..a5429dd
> > --- /dev/null
> > +++ b/Documentation/leds/leds-one-shot-timer.txt
> > @@ -0,0 +1,79 @@
> > +
> > +LED one shot timer feature
> > +===========================
> > +
> > +LED infrastructure lacks support for one shot timer trigger and activation.
> > +The current support allows for setting two timers, one for specifying how
> > +long a state to be on, and the second for how long the state to be off. For
> > +example, delay_on value specifies the time period an LED should stay in on
> > +state, followed by a delay_off value that specifies how long the LED should
> > +stay in off state. The on and off cycle repeats until the trigger gets
> > +deactivated. There is no provision for one time activation to implement
> > +features that require an on or off state to be held just once and then stay
> > +in the original state forever.
> > +
> > +This feature will help implement vibrate functionality which requires one
> > +time activation of vibrate mode without a continuous vibrate on/off cycles.
> > +
> > +This patch implements the timer-no-default trigger support by enhancing the
> > +current led-class, led-core, and ledtrig-timer drivers to:
> > +
> > +- Add support for forever timer case. forever tag can be written to delay_on
> > +  or delay_off files. Internally forever is mapped to ULONG_MAX with no timer
> > +  associated with it.
> > +
> > +- The led_blink_set() which takes two pointers to times one each for delay_on
> > +  and delay_off has been extended so that a NULL instead of a pointer means
> > +  "forever".
> > +
> > +- Add a new timer-no-default trigger to ledtrig-timer
> > +
> > +The above enhancements support the following use-cases:
> > +
> > +use-case 1:
> > +echo timer-no-default > /sys/class/leds/SOMELED/trigger
> > +echo forever > /sys/class/leds/SOMELED/delay_off
> > +echo 2000 > /sys/class/leds/SOMELED/delay_on
> > +
> > +When timer-no-default is activated in step1, unlike the timer trigger case,
> > +timer-no-default activate routine activates the trigger without starting
> > +any timers. The default 1 HZ delay_on and delay_off timers won't be started
> > +like in the case of timer trigger activation. Not starting timers ensures
> > +that the one time state isn't stuck if some error occurs before actual timer
> > +periods are specified. delay_on and delay_off files get created with 0
> > +values. Please note that it is important to set delay_off to forever prior
> > +to setting delay_on value. If the order is reversed, the LED will be turned
> > +on, with no timer set to turn it off.
> > +
> > +When delay_off value is specified in step 2, delay_off_store recognizes the
> > +special forever tag and records it and returns without starting any timer.
> > +Internally forever maps to ULONG_MAX. The led_blink_set() which takes
> > +two pointers to times one each for delay_on and delay_off has been extended
> > +so that a NULL instead of a pointer means "forever".
> > +
> > +When delay_on value is specified in step 3, a timer gets started for
> > +delay_on period, and delay_off stays at ULONG_MAX with no timer associated
> > +with it.
> > +
> > +use-case 2:
> > +echo timer-no-default > /sys/class/leds/SOMELED/trigger
> > +echo forever > /sys/class/leds/SOMELED/delay_on
> > +echo 2000 > /sys/class/leds/SOMELED/delay_off
> > +
> > +When timer-no-default is activated in step1, unlike the timer trigger case,
> > +timer-no-default activate routine activates the trigger without starting
> > +any timers. The default 1 HZ delay_on and delay_off timers won't be started
> > +like in the case of timer trigger activation. Not starting timers ensures
> > +that the one time state isn't stuck if some error occurs before actual timer
> > +periods are specified. delay_on and delay_off files get created with 0
> > +values. Please note that it is important to set delay_on to forever prior
> > +to setting delay_off value. If the order is reversed, the LED will be turned
> > +off, with no timer set to turn it back on.
> > +
> > +When delay_on value is specified in step 2, delay_on_store recognizes the
> > +special forever tag and records it and returns without starting any timer.
> > +Internally forever maps to ULONG_MAX.
> > +
> > +When delay_off value is specified in step 3, a timer gets started for
> > +delay_off period, and delay_on stays at ULONG_MAX with no timer associated
> > +with it.
> 
> Having looked at the code and read through the thread and Andrew's patch
> review, I'm left wondering why you didn't add a new trigger for this
> functionality?

By new trigger do you mean, adding another interface to struct
led_trigger. My first patch to solve this use-case indeed did that. I
still happen to have a copy of that patch. It would require more changes
to the infrastructure than this approach, however it is more explicit
and clear.

static struct led_trigger gpio_led_trigger = {
       .name           = "gpio",
+       .activate_once  = NULL,
       .activate       = gpio_trig_activate,
       .deactivate     = gpio_trig_deactivate,
};
> 
> The reason I ask that there do seem to be a number of questions about
> backwards compatibility and this also seems to complicate the standard
> timer trigger in non-obvious ways. Having a new trigger for this
> functionality would allow for a much clearer namespace and no backwards
> compatibility issues. It also means additional functionality can be
> added later in a contained place. I'm wondering if there is a downside
> to a separate trigger I'm missing?

Please see above. I can send that patch for draft review if you would
like to see it. I haven't done a lot of testing on that patch and also I
think I have a few missing pieces. But I am open to either approach.

> 
> Dimity raises some valid questions about the force-feedback framework in
> the input system too. We need to make a decision about where phone
> vibration framework belongs and then stick to that. You can argue this
> to either subsystem, neither "led" or "input" is a obvious description
> of phone vibration at a first glance!

force-feedback framework is another alternative. Making a decision is
great, what are the next steps to get closer to making a call? 

Thanks,
-- Shuah
> 
> Cheers,
> 
> Richard
> 
> 
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