Re: ACPI C4 support

Bruno Ducrot
2004-03-01T19:39:17Z

On Mon, Mar 01, 2004 at 08:27:38PM +0100, Pavel Machek wrote:
> Hi!
>
> > > [mailto:acpi-devel-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org] On Behalf Of
> > > Stefan Behlert
> > > > No. pblk_length is 0 or 6. Not 5 nor 7 ;)
> > >
> > > Sorry, I don't understand: We've a Laptop with a DSDT with
> > > Processor (\_PR.CPU0, 0x01, 0x00001010, 0x07)
> > > in it.
> > > Comment from the responsible BIOS-team:
> > > "Our processor block object is 7 bytes in length because we
> > > also support
> > > C4 (P_LVL4) which is at <P_BLK>+6. Therefore, the
> > > size/length must be
> > > reported as 7 and not 6."
> > >
> > > Is the '7' the BIOS-developer mentioned the same '7' as
> > > mentioned by you?
> >
> > This is wrong.
> >
> > There is confusion here because what older systems do on C3 is different
> > from what more recent systems do on C3, at the electrical level. I know
> > at least internally the improved C3-like state was called "C4" but to
> > the OS it just looks just like C3, and the value for C4 should go in
> > P_LVL3. P_BLK length should remain 6.
> >
> > The only way to get more than C1, C2, and C3 is via the _CST object.
> >
> > Please tell the BIOS developer this. I have an old BIOS developers guide
> > version that agrees with them but I just asked the experts internally
> > and they said no.
>
> If there is old BIOS guide telling them to use length of 7, could we
> make Linux accept that? Its likely a lot of developers have read
> that...
>
> Allowing length of 7 is one line change; if we do it, such notebooks
> will be able to use C1..C3, but not C4. That does not seem too bad...
>

The problem is that, from strict acpi point of view, it will be too easy
to allow '7', and _CST support is much better. Don't ask me why, I'm not
an expert. So perhaps it may be possible to add the (bahh, beurk)
length of 7 if there exist a bad written bios developper guide released
apparently by Intel, at least as a non pedantic acpi option?

--
Bruno Ducrot

-- Which is worse: ignorance or apathy?
-- Don't know. Don't care.