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    SubjectRe: [PATCH RESEND] LEDS-One-Shot-Timer-Trigger-implementation
    On Mon, Apr 09, 2012 at 09:42:19AM +1000, NeilBrown wrote:
    > On Sat, 7 Apr 2012 14:56:41 -0700 Dmitry Torokhov <dmitry.torokhov@gmail.com>
    > wrote:
    >
    > > Hi Shuah,
    > >
    > > On Sat, Apr 07, 2012 at 08:13:44AM -0600, Shuah Khan wrote:
    > > >
    > > > > > +This feature will help implement vibrate functionality which requires one
    > > > > > +time activation of vibrate mode without a continuous vibrate on/off cycles.
    > > > >
    > > > > They make vibrating LED? ;)
    > > > >
    > > > > What's going on here? You're proposing to repurpose the LEDs code to
    > > > > drive vibration devices? Or some devices couple a LED with a vibration
    > > > > device?
    > > >
    > > > I owe you filling in the blanks type explanation. Let me describe the
    > > > use-case I am trying to address first. Vibrater function on phones is
    > > > implemented using PWM pins on SoC or PMIC. When there is no such
    > > > hardware present, a software solution is needed. Currently two drivers
    > > > timed-gpio and timed-output (under staging/android in Linux 3.3)
    > > > together implement the software vibrate feature. The main functionality
    > > > it implements is the one time enables of timer to prevent user space
    > > > crashes leaving the phone in vibrate mode causing the battery to drain.
    > > > leds as it is implemented currently, is not suitable to address this
    > > > use-case as it doesn't support one time enables.
    > >
    > > So why do not you use memoryless force feedback framework that other
    > > devices use (see drivers/input/misc/*vibra.c drivers).
    > >
    > > Thanks.
    > >
    >
    > I don't see that using a "force feedback" "input" device to control a
    > vibrator - which is neither "force feedback" nor "input", makes any more
    > sense than using an "led" device to control something that isn't an LED.
    > So we are even there.

    Well, if you consider "input" is really "hid" then FF is really
    appropriate for iterfacing with a human.

    >
    > I think driving leds by writing to sysfs files is lot easier (for scripting
    > languages particularly) than the ioctls or binary writes needed for managing
    > input devices.
    >
    > Of course, if the 'input' framework were used for controlling all LEDs -
    > rather than just the LEDs on keyboard - then it might make sense...
    >
    > Also, I don't think 'ff' allows for "vibrate for N milliseconds".
    > It appears that one uses the "rumble" effect and have to say "turn it on",
    > then "turn it off". Is that correct?

    No, it is not.

    > I found 'struct ff_replay' which has a 'length' which is a duration, but it
    > doesn't seem to be used.

    It does, see drivers/input/ff-memless.c where it us used to schedule
    when effect starts and how long it should play. Non memoryless devices
    (such as iforce) are supposed to schedule effects themselves.

    >
    > How would you tell the force feedback framework to play the vibrator for
    > 120ms, then stop?

    By specifying replay->length = 120

    Thanks.

    --
    Dmitry


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