Re: Linux 2.6.20-rc6 - sky2 resume breakage

[Len Brown <lenb@kernel.org>]

On Monday 29 January 2007 19:12, Linus Torvalds wrote:
> 
> On Mon, 29 Jan 2007, Stephen Hemminger wrote:
> > 
> > Why do you insist on maintaining the wrong initialization order
> > on resume? When I raised the issue, Len brought up that the resume
> > order did not match spec, but then there has been slow progress
> > in fixing it (it's buried in -mm tree).
> 
> It's not getting merged, SINCE IT DOESN'T WORK. It causes all sorts of 
> problems, because ACPI requires all kinds of things to be up and running 
> in order to actually work, and that in turn breaks all the devices that 
> have different ordering constraints.
> 
> ACPI is a piece of sh*t. It asks the OS to do impossible things, like 
> running it early in the config sequence when it then at the same time 
> wants to depend on stuff that are there *late* in the sequence. It's not 
> the first time this insane situation has happened, either.

And it will not be the last:-)

There are really two cases, one is easy, one hard:

1. The ACPI spec and our knowledge of how the HW and talking to our own BIOS
    folks tells us quite a bit about how things are supposed to work.

2. "Windows Bug Compatibility" (tm)
    When OEMs build systems and test them only with Windows, then
    the implementation quirks of Windows get ingrained in the platforms.
    Linux then tries to run on the same platform and wonders why
    the BIOS does "unusual" things.  The answer is because it has been
    only tested on Windows and BIOS quirks slip through Windows testing.

    To be fair, the exact same thing would happen in reverse to Windows
    if vendors only tested with Linux.

    http://www.linuxfirmwarekit.org/ is intended to help mitigate some of this
    problem.  So at least vendors that care about Linux can make sure that
    they minimize the curve balls they throw us.

An example of a recent curve ball is when the BIOS supplies two APIC (MADT)
tables.  Well, the spec says there should be only one...  We have proof
that Windows doesn't use the 1st for enumerating processors because
Windows works on a box with a garbled 1st table.
If we prove that Windows doesn't use the second either then it means
they enumerate processors  via the DSDT -- which means bringing up
the ACPI interpreter before bringing up SMP -- and that would require
a significant change to Linux boot sequence...

> But we'll try to merge the patch that totally switches around the whole 
> initialization order hopefully early after 2.6.20. But no way in hell do 
> we do it now, and I personally suspect we'll end reverting it when we do 
> try it just because it will probably break other things. But we'll see.

I agree with this plan, and I concur with your outlook.

I think Rafel is holding the ball here as we wait for an SMP-safe freezer:
http://lists.osdl.org/pipermail/linux-pm/2006-December/004233.html

cheers,
-Len