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 10:15 +0000, Gonglei (Arei) wrote:
> Hi, 
> 
> First, please forgive me for my bad English.
> It's so sad.
> 
> > -----Original Message-----
> > From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> > Sent: Friday, May 09, 2014 5:57 PM
> > To: Gonglei (Arei)
> > Cc: Jan Beulich; xen-devel@xxxxxxxxxxxxx; anthony.perard@xxxxxxxxxx;
> > stefano.stabellini@xxxxxxxxxxxxx; johannes.krampf@xxxxxxxxxxxxxx; Gaowei
> > (UVP); Hanweidong (Randy); Huangweidong (C); kevin@xxxxxxxxxxxx;
> > fabio.fantoni@xxxxxxx; qemu-devel@xxxxxxxxxx; mst@xxxxxxxxxx
> > Subject: Re: [PATCH v4] Hvmloader: Modify ACPI to only supply _EJ0 methods
> > for PCIslots that support hotplug by runtime patching
> > 
> > On Fri, 2014-05-09 at 09:45 +0000, Gonglei (Arei) wrote:
> > > > And it also seem pretty pointless to send a v4 without addressing
> > > > all comments you got on v3.
> > > >
> > > I don't think so. I have absorbed Ian's all suggestion on v3. And for 
> > > other
> > > questions have been answered too, in despite of is me or not.
> > 
> > Actually you haven't answered "Why is runtime patching the only
> > option here?" which was originally phrased as:
> > > > Which appears to involve an awful lot of jumping through hoops... Please
> > > > can you explain why it is necessary, as opposed to e.g. using a dynamic
> > > > set of SSDTs?
> > 
> Ian, I understand your mean now, which consider our method to address 
> this issue is maybe unnecessary, right? And you suggest us to use a dynamic 
> set of SSDTs.

Really what I'm asking is what set of constraints and requirements led
you to this particular solution.

I think the method seems complicated, and I'd therefore like to know why
it was preferred over other alternatives, or perhaps why it is the only
option.

> TBH I don't know more about the dynamic SSDTs, if you have any details, 
> tell me please, thanks in advance!

I'm not an ACPI expert, but AIUI an SSDT is essentially a little piece
of DSDT which is grafted onto the main DSDT at runtime by the OSPM. They
make it somewhat easier for BIOS (or ACPI table) authors to include or
exclude functionality at runtime, perhaps on a physical system in
response to a user changing something in the BIOS setup screens. In Xen
we appear to use SSDTs for HPET, TPM and S3/S4 functionality, depending
on the guest configuration
(hvmloader/acpi/build.c:construct_secondary_tables()).

Ian.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel