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    SubjectRe: 2.6.19: ACPI reports AC not present after resume from STD
    Date
    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
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