RE: [Xen-devel] Re: Paravirtualizing bits of acpi access

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Len Brown [mailto:lenb@xxxxxxxxxx] 
>Sent: 2009年3月28日 9:02
>> > Jeremy, I'm not excited about a proposed change to acpixf.h --
>> > this is the API to ACPICA...
>> >   
>> Do you have an issue with the mechanism (using weak 
>function, etc), or just
>> the placement of the prototypes in that header?  Would there 
>be a better
>> header to put them in?  Or would you prefer some other mechanism?
>> 
>> It certainly seems like Xen and tboot should be able to 
>share the same hook,
>> given that they're doing similar things for similar reasons.
>> 
>> (I don't really understand the structure of all the acpi 
>stuff; I'm just
>> wading in and making a mess of things until I can close the 
>lid of laptop
>> successfully.)
>
>Everything in acpi/acpica/ is source code that we share with BSD
>via the ACPICA project http://acpica.org/
>
>ACPICA also supplies a couple of the headers outside that directory,
>eg. acpixf.h, which is the API between the kernel and ACPICA.
>
>We can, and do, change that API when it makes sense.
>However, we want to think carefully before changing it,
>for we either cause Linux to diverge, or we have to sell
>the same change to several other operating systems.
>So ideally we wouuld need to make no Linux-specific, or Xen-specific
>changes in that directory.
>
>One possibility is to have this called via
>function pointer from ASM and scribble over the default
>function pointer for the Xen case.  In that case, the Xen
>version of the routine would live someplace other than acpi/acpica/ -
>someplace with the word xen in the path.  If using _weak can 
>effectively
>do that at link time, then fine, if we can do it w/o changing 
>the API --
>a _weak annotation is an easy ACPICA/Linux divergencen to manage.
>
>I don't know if Xen and TXT are exclusive, or if we'd ever need
>to handle both cases at the same time.  I guess that will influence
>if the TXT and Xen use the same approach or something different.
>

When only Xen exists, S3 flow is:
dom0 S3 -> Xen S3

When only TXT is enabled, it's:
dom0 S3 -> TXT S3

When both Xen and TXT exist, TXT is not exposed to dom0 and thus
the S3 flow is:
dom0 S3 -> Xen S3 -> TXT S3

I.e, dom0 only needs to care one case at given time. Transition to
TXT is only required if system software is the lowest level on top of
hardware.

Thanks
Kevin

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