Re: [Xen-devel] [PATCH v4] Hvmloader: Modify ACPI to only supply _EJ0 methods for PCIslots that support hotplug by runtime patching

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-05-09 at 10:38 -0400, Ross Philipson wrote:
> >> Can it be used to patch the DSDT? Or were you (Ian) thinking that the bulk
> >> of the ACPI PCI stuff can be moved there ?
> >
> > I think it can "shadow" or extend existing DSDT stuff, I don't think it
> > can patch as sych. But here we want to dynamically add an entire method
> > I think? (or hide, but I don't think that is possible).
> 
> Yea the SSDTs extend the DSDT. The DSDT is loaded to create the name 
> space and then SSDTs are loaded and added to the name space. If you need 
> to make runtime modifications like this, it is much easier to do it in 
> an SSDT as you suggest. What I don't know is whether you could extend 
> say a device, as in this case, with with a single method in a separate 
> SSDT. I have never really seen something like that before.

So it could be used by having two template SSDTs (one for ejectable, one
for not) and outputting the correct ones as necessary?

> WRT to hide vs. remove, I believe the intent is to effectively remove 
> the eject method from a given device by renaming it. It could simply be 
> removed making the device not eject-able but I think they are trying to 
> avoid having to recalculate and update the checksum on the DSDT.

How does one make the device be not eject-able? I thought it was via the
presence or absence of _EJ0 (hence the renaming hack).

> As to whether this has to be done at runtime, I don't know. If it does, 
> I wrote a lib that can generate basically any (rev2) AML on the fly. We 
> used it e.g. to generate WMI functionality in an SSDT at runtime. I 
> would be happy to share if it is useful.

Thanks. hvmloader seems to generate various bits on the fly based on
basic templates already, although perhaps those cases are simpler than
this one.

Ian.


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