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SubjectRe: [2/2] 2.6.21-rc7: known regressions
On Mon, Apr 16, 2007 at 03:16:37AM +0200, Adrian Bunk wrote:
> On Sun, Apr 15, 2007 at 08:54:46PM -0400, Dave Jones wrote:
> > On Mon, Apr 16, 2007 at 02:37:23AM +0200, Adrian Bunk wrote:
> >
> > > Subject : ThinkPad X60: resume no longer works (PCI related?)
> > > workaround: booting with "hpet=disable"
> > > References :
> > > Submitter : Dave Jones <>
> > > Jeremy Fitzhardinge <>
> > > Caused-By : PCI merge
> > > commit 78149df6d565c36675463352d0bfe0000b02b7a7
> > > Handled-By : Eric W. Biederman <>
> > > Rafael J. Wysocki <>
> > > Status : unknown
> >
> > note that this workaround doesn't seem to work in all cases.
> > Mine may a slightly different model (I have the tablet version)
> > but disabling hpet shows the same regression.
> > I've been fighting Eric's USB debug cable code in the hope
> > of getting _something_ useful out of it other than a black screen,
> > but I've been getting nowhere with it.
> I'm not sure why I thought you two ran into the same regression.

I'm not sure why I never hit the same bug that Jeremy did
(again, maybe subtle hardware differences between our models),
but I finally got somewhere. -rc7 with the same config I've
been testing exhibited exactly the same bug. Disabling
the FB_BACKLIGHT option (and all the FB drivers that 'select' it),
I get a working display on resume again.

This makes a lot of sense. As before, when I resumed, the backlight
wasn't coming back on, but I knew the machine was alive, as
capslock was working. (Amusingly, I never noticed the backlight
wasn't coming back on until tonight, when I started debugging this
with the lights off. Late-night debugging ftw).

I'll try and narrow down exactly where it's failing in the
backlight code next, but it's getting late here, so I may
leave this until tomorrow for further investigation.
Some other clues for anyone playing along at home:
This X60 has Intel graphics. ie, I'm not using any of
the drivers that 'select FB_BACKLIGHT', so somewhere in
the common fb code is code that I'm guessing is dependant
upon the framebuffer driver doing something or other
if FB_BACKLIGHT is set.

(Adding Richard to Cc: as he seems to be responsible for
the FB backlight code from what I can tell.)


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