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    SubjectRe: [PATCH] leds: use led_brightness_set in led_trigger_event
    On Mon, Jun 11, 2012 at 03:38:25PM -0600, Shuah Khan wrote:
    > On Mon, 2012-06-11 at 22:57 +0200, Fabio Baltieri wrote:
    > > Fix led_trigger_event() to use led_brightness_set() instead of
    > > led_set_brightness(), so that any pending blink timer is stopped before
    > > setting the new brightness value. Without this fix LED status may be
    > > overridden by a pending timer.
    > >
    > > This allows a trigger to use a mix of led_trigger_event(),
    > > led_trigger_blink() and led_trigger_blink_oneshot() without races.
    > >
    > > Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com>
    > > Cc: Bryan Wu <bryan.wu@canonical.com>
    > > ---
    > > Hi Bryan,
    > >
    > > I found this one while working on another patch but I think it's also needed by
    > > other drivers which mixes led_trigger_blink() and led_trigger_event(), such as
    > > power_supply_leds.
    > >
    > > Without this a led don't stop blinking as it should when calling
    > > led_trigger_event().
    >
    > Good find. This is very subtle race though because both timer and
    > oneshot triggers call led_brightness_set() from their deactivate
    > routines. Is this when these events triggered using oneshot trigger?

    Actually that was when mixing blink (both timer and oneshot, they use
    the same timer) and standard trigger-event-set. It should be safe if
    only internal (core) functions call set_brightness.

    > >
    > > Should not cause any harm on other drivers.
    > >
    > > (I'm starting to find the whole led_set_brightness/led_brightness_set thing a
    > > bit confusing BTW...)
    >
    > I agree with the names are confusing. :) It found it confusing as well.
    > Probably why we have this bug hiding until led_trigger_blink() came
    > along.
    >
    > led_brightness_set() calls led_set_brightness(). led_set_brightness()
    > takes cares about whether the driver is in suspend state and invokes
    > driver's brightness_set interface. Maybe led_clear_blink_timer() would
    > be a better name for this led_brightness_set() routine.

    I think maybe we should just rename the function to led_set_brightness()
    for the safe one (the one whichh also deactivate the time) and
    _led_set_brightness() for the internal one, to put some emphasis to the
    "internal" nature of the second.

    > I can volunteer to make this change if we agree that this will be a good
    > one to clear this naming confusion.

    That would save some headache in the future! :-)

    Fabio

    >
    > -- Shuah
    >
    > >
    > > Fabio
    > >
    > > drivers/leds/led-triggers.c | 2 +-
    > > 1 file changed, 1 insertion(+), 1 deletion(-)
    > >
    > > diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
    > > index fa0b9be..b88d3b9 100644
    > > --- a/drivers/leds/led-triggers.c
    > > +++ b/drivers/leds/led-triggers.c
    > > @@ -224,7 +224,7 @@ void led_trigger_event(struct led_trigger *trig,
    > > struct led_classdev *led_cdev;
    > >
    > > led_cdev = list_entry(entry, struct led_classdev, trig_list);
    > > - led_set_brightness(led_cdev, brightness);
    > > + led_brightness_set(led_cdev, brightness);
    >
    > This is in-line with led_trigger_set() which is calling
    > led_bightness_set() correctly. Also led_classdev_unregister() calls it I
    > think for the same reason so the blink timer can be stopped.
    >
    > > }
    > > read_unlock(&trig->leddev_list_lock);
    > > }
    >
    >


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