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From: Matthias Hopf on 3 Aug 2010 06:20
A bit of background about this patch:


acpi_video_bus_get_devices() explicitly calls acpi_video_device_enumerate()
before acpi_video_bus_get_one_device(), which does acpi_video_device_bind().

In _enumerate(), active_list[] is created, with .bind_info explicitly set to
NULL, while the related .bind_info entry in video_device_list is set to the
acpi_video_device ptr in _bind().

The .bind_info is later used in acpi_video_resume() to re-set the backlight
- but it's only evaluated on the active_list[], on which all .bind_info are
NULL by construction. This results in backlight not being restored, if the
BIOS doesn't do this by itself already.


The patch resolves this by replacing the active_list[] traversal by a
video_device_list traversal, but due to the nature of the issue I'm unsure
whether the original issue isn't of more principal quality. I don't understand
why the list is (partially) transformed into an array in the first place,
especially as both the array *and* the list are used in the code...


Thanks

Matthias

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From: Matthias Hopf on 4 Aug 2010 07:10
On Aug 04, 10 09:27:29 +0800, Zhang Rui wrote:
> On Tue, 2010-08-03 at 18:11 +0800, Matthias Hopf wrote:
> > The .bind_info is later used in acpi_video_resume() to re-set the backlight
> > - but it's only evaluated on the active_list[], on which all .bind_info are
> > NULL by construction.
> why? .bind_info in active_list is initialized in acpi_video_device_bind.

Hm. Right. acpi_video_bus_get_one_device() is called after _enumerate().
Dunno why I didn't read this correctly.

> > I don't understand
> > why the list is (partially) transformed into an array in the first place,
> > especially as both the array *and* the list are used in the code...
> >
> no, the active_list is an array in fact, which equals
> acpi_video_bus->attached_array. Maybe we need to change it to a more
> proper name.

:-)

> I'm still wondering why the patch works for you.

Same to me.

> could you please attach the acpidump output of this laptop?

Will do.

> please rebuild your kernel with CONFIG_ACPI_DEBUG=y, and reboot with
> kernel parameter "acpi.debug_layer=0x10 acpi.debug_level=0x400".
> and attach the dmesg output after resume, both w/ and w/o the patch you
> attached.

The most intriguing thing here is that the system starts writing to
/var/log/messages continuously, thus dmesg output is sort-of worthless.
This might be a reasonable side effect, it might be an indication of the
original issue.
I'll try to compile something for you.

Thanks

Matthias

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