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    SubjectRe: [PATCH 2.6.8.1 0/2] leds: new class for led devices
    On Fri, Sep 03, 2004 at 07:09:59PM +0000, John Lenz wrote:
    > > > The led class does not really inforce any policy, it just passes this
    > > > number along to the actual driver that is registered. So say you had
    > > > a led that could be red, green, or both red and green at the same time
    > > > (not sure how that would work hardware wise, but ok).
    > >
    > > See Netwinders. They have a bi-colour LED which has independent red
    > > and green LEDs in the same package. When they're both on it's yellow.
    > >
    > > It's _VERY_ useful to see the green LED flashing and know that the
    > > headless machine is running, or that the red LED being on means that
    > > either it hasn't booted a kernel yet or the system has successfully
    > > shut down.
    > >
    > > It means I don't have to fsck around with monitor cables before pulling
    > > the power.
    > >
    > > And no, doing that from userspace won't work because userspace is dead
    > > _before_ the system has finished shutting down (see drive cache
    > > flushing on shutdown.)
    > >
    > > It's also _VERY_ useful to know whether the kernel has managed to get
    > > far enough through the boot that the heartbeat LED is flashing but
    > > maybe not sufficiently to bring up the serial console as well -
    > > again another thing that a userspace implementation will never be
    > > able to support.
    >
    > Hey I agree! I use the led as a debugging tool on the Sharp Zaurus.
    > Before I had the framebuffer or the serial port working, being able to see
    > the led told me something was working :) This patch isn't really intended
    > for debugging support, so perhaps some other interface could be added.
    >
    > On the other hand, perhaps we can just do a #ifdef LEDS_DEBUGGING that
    > would toggle the led on a timer.

    You missed the point. The above scenarios I was describing are _not_
    debugging.

    --
    Russell King
    Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
    maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
    2.6 Serial core
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