Re: Suspend-to-RAM on Sony Vaios

[Andi Kleen <ak-l3A5Bk7waGM@public.gmane.org>]

On Wed, Nov 03, 2004 at 02:52:04PM +0100, ole.rohne-vJEk5272eHo@public.gmane.org wrote:
> Andi> On Wed, Nov 03, 2004 at 12:31:46PM +0100, ole.rohne-vJEk5272eHo@public.gmane.org wrote:
> Andi> Or rather not apply this. I have no plans to support switch back
> Andi> to real mode on x86-64. It is just far too hackish and fragile.
> >> 
> >> I agree that return to real mode is kind of *hackish* - but I do not
> >> agree that it has to be *fragile*. I'd like to repeat my general
> >> comments on the alternatives, not particularly connected to x86-64:
> 
> Andi> I very much doubt it you can get it reliable because it's such an 
> Andi> extremly intrusive operation. 
> 
> Why do you say so? As we're resuming from S3 sleep, we've just come
> out of real mode anyway, and we're just relying on the same mechanism
> to work twice. We need of course to be careful setting up the real

The big difference is that the kernel does all kind of complicated
things to shut itself up first. What you're trying is to do the
same thing halfway through the initialization sequence when
a lot of hardware is already running again. Especially on x86-64
going back out of long mode is a really intrusive operation,
killing all interrupt state etc.

> Andi> Either do it before switching to protected/long mode or later
> Andi> in a emulator.
> 
> >> Properly supporting the "POST before switching to PM" would require a
> >> full real-mode bus/device resume. The ACPI specs doesn't even
> >> guarantee a working southbridge at real mode resume.
> 
> Andi> Not sure what you mean with "working southbridge". 
> 
> I'm not really sure myself... I'm just trying to understand why the
> original s3_bios just plainly doesn't work on some machines. The ACPI
> specs only guarantee memory mapping
> 
> Andi> If you need PCI why not call the PCI BIOS to initialize it
> Andi> first?
> 
> I'm sure that could be tried... I'd guess this is the way Windows does
> it, initializing everything and the kitchen sink before even returning
> to PM.

You just need to initialize the same things the boot BIOS does before
calling the video POST after power up.  That would be probably AGP and PCI. 

I hope the PCI BIOS has a function for this though. I don't have
a spec for it unfortunately.

> There is just too much stuff even in kernel space that depends on the

The only code in the kernel that should care about video mode
state is the fbcon console driver. Possibly DRI too, but those
are firmly under user control and can be handled by the X server.

-Andi


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