Re: 2.6.19: ACPI reports AC not present after resume from STD

Rafael J. Wysocki
2007-02-25T10:58:07Z

On Sunday, 25 February 2007 11:37, Andrey Borzenkov wrote:
> On Воскресенье 25 февраля 2007, Rafael J. Wysocki wrote:
> > On Sunday, 25 February 2007 00:26, Andrey Borzenkov wrote:
> > > On Суббота 24 февраля 2007, Rafael J. Wysocki wrote:
> > > > Hi,
> > > >
> > > > On Saturday, 24 February 2007 10:55, Andrey Borzenkov wrote:
> > > > > On Вторник 13 февраля 2007, Andrey Borzenkov wrote:
> > > > > > On Четверг 07 декабря 2006, Lebedev, Vladimir P wrote:
> > > > > > > Please register new bug, attach acpidump and dmesg.
> > > > > >
> > > > > > http://bugzilla.kernel.org/show_bug.cgi?id=7995
> > > > > >
> > > > > > regards
> > > > >
> > > > > Well, this starts looking like ACPI is not at fault.
> > > > >
> > > > > When reporting AC state ACPI just reads contents of system memory (I
> > > > > presume it gets updated by BIOS/ACPI when AC state changes). It looks
> > > > > like this memory area is restored during resume from STD. I updated
> > > > > mentioned bug report with more detailed description. Now if someone
> > > > > could suggest a way to catch if specific physical address gets
> > > > > saved/restored this would finally explain it.
> > > >
> > > > First, if you want the reserved memory areas to be left alone by
> > > > swsusp, you need to mark them as 'nosave'. On x86_64 this is done by
> > > > the function e820_mark_nosave_range() in arch/x86_64/kernel/e820.c that
> > > > can be ported to i386 with no problems. However, we haven't found that
> > > > very useful, so far, since no one has ever reported any problems with
> > > > the current approach, which is to save and restore them.
> > >
> > > Well, the following proof of concept patch fixes this issue for me.
> > > Please notice that original version of e820_mark_nosave_range() could
> > > fail to exclude some areas due to alignment issues (exactly what happened
> > > to me on first try) so it still can explain your problem too.
> >
> > Great job, thanks for the patch! It looks good, so I'm going to forward it
> > for merging.
> >
>
> Please no; I'm currently testing slightly more polished version; I will send
> it later.

OK

> Could anybody explain (or give pointer to) what happens which region that is
> not page-aligned? In particular, the very first one:
>
> BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
> BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
>
> Will the kernel allocate partial page (how?) or will the kernel ignore last
> (first) incomplete page? In the former case how those incomplete pages can be
> detected?

Well, on x86_64, if I understand e820_register_active_regions() correctly,
the partial pages won't be registered.

Greetings,
Rafael