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    SubjectRe: 2.6.21-rc1 dims my LCD
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    On Mon, 2007-02-26 at 16:24 +0100, Jiri Kosina wrote:
    > On Mon, 26 Feb 2007, Richard Purdie wrote:
    >
    > > Jiri: I've appended a patch that should already be queued, could you
    > > test and see if it solves the problem.
    >
    > Thanks. In the meantime I have gone through the code and I can confirm
    > that this is the root cause of what I am observing.
    >
    > Now regarding the patch - at the time when the dim happened previously,
    > currently there is a observable blink (after which the brightness is
    > correct).

    The reason for the behaviour is that its turning the backlight down/off
    to save power as it thinks the screen is blank. The blink therefore
    makes sense as far as the backlight class is concerned and its working
    as intended now.

    > I have put some debugging printk() into fb_notifier_callback(),
    > and it turns out that on FB_EVENT_CONBLANK, there are two successive calls
    > to backlight_update_status(), second immediately following the first one:
    >
    > Feb 26 15:11:14 thunder kernel: calling backlight_update_status() with bd->props.fb_blank == 1, bd->props.brightness == 0
    > Feb 26 15:11:14 thunder kernel: calling backlight_update_status() with bd->props.fb_blank == 0, bd->props.brightness == 0
    >
    > Is this really a right thing to do?

    This should come from two calls to fbcon_generic_blank() in
    drivers/video/console/fbcon.c with a different blank parameter and is
    therefore in a way outside the scope of the backlight class.

    It would be interesting to know why it decides to blank then immediately
    unblank the display though. I've cc'd the fbdev-devel list.

    Richard


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