Re: [Qemu-devel] [PATCH 3/3] Get system state configuration from QEMU and patch DSDT with it.

[Gleb Natapov <gleb@redhat.com>]

On Sun, May 20, 2012 at 03:30:50PM +0300, Avi Kivity wrote:
> On 05/20/2012 03:15 PM, Gleb Natapov wrote:
> > On Sun, May 20, 2012 at 02:44:51PM +0300, Avi Kivity wrote:
> > > On 05/20/2012 12:03 PM, Gleb Natapov wrote:
> > > > QEMU may want to disable guest's S3/S4 support and it wants to distinguish
> > > > between regular powerdown and S4 powerdown. To support that new fw_cfg
> > > > option was added that passes supported system states and what value should
> > > > guest use to enter each state. States are passed in 6 byte array. Each
> > > > byte represents one system state. If byte at offset X has its MSB set
> > > > it means that system state X is supported and to enter it guest should
> > > > use the value from lowest 7 bits. Patch also detects old QEMU and uses
> > > > values that work in backwards compatible way there.
> > > >
> > > 
> > > 
> > > Do we actually have to patch the DSDT?  Or can _S3 etc be made into
> > > functions instead? (and talk to the bios, or even to fwcfg directly?)
> > > 
> > We better not talk to fwcfg after OSPM is started since this is firmware
> > confing interface.
> 
> Why not?  The OS isn't going to talk to it, so we can have a driver in ACPI.
> 
The OS is going to talk to it since the OS is the one who interprets
AML. We may want to disable fwcfg after OS bootup at all in the feature.
Who knows what kind of sensitive information we may want to pass by it
in the feature? May be something TPM related? And I do not see any advantage
of using fwcfg from AML.

> >  Regardless, presence of _S3 name or method is all
> > that needed for OS enabling S3 option. If _S3 is defined as a method it
> > has to return Package() otherwise iasl refuses to compile it.
> 
> Can't we Return (Package (...) { ... }) or equivalent? 
> 
We can, how does it help?

--
			Gleb.