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

[Gonglei (Arei)]

> From: Konrad Rzeszutek Wilk [mailto:address@hidden
> Sent: Thursday, August 21, 2014 6:31 AM
> To: Fabio Fantoni
> Cc: Ross Philipson; Ian Campbell; Paul Durrant; address@hidden;
> Huangweidong (C); Hanweidong (Randy); address@hidden;
> address@hidden; address@hidden;
> address@hidden; Gonglei (Arei); Stefano Stabellini; Gaowei
> (UVP); Jan Beulich; Anthony Perard
> Subject: Re: [Xen-devel] [PATCH v4] Hvmloader: Modify ACPI to only supply _EJ0
> methods for PCIslots that support hotplug by runtime patching
> 
> On Wed, Aug 20, 2014 at 02:11:48PM +0200, Fabio Fantoni wrote:
> > Il 12/05/2014 16:32, Ross Philipson ha scritto:
> > >On 05/12/2014 05:05 AM, Ian Campbell wrote:
> > >>On Fri, 2014-05-09 at 13:32 -0400, Ross Philipson wrote:
> > >>>On 05/09/2014 12:34 PM, Paul Durrant wrote:
> > >>>>>-----Original Message-----
> > >>>>>From: Ian Campbell
> > >>>>>Sent: 09 May 2014 17:12
> > >>>>>To: Konrad Rzeszutek Wilk
> > >>>>>Cc: Ross Philipson; address@hidden; Huangweidong (C);
> Hanweidong
> > >>>>>(Randy); address@hidden; address@hidden; xen-
> > >>>>>address@hidden; address@hidden;
> > >>>>>address@hidden; Gonglei (Arei); Stefano Stabellini;
> > >>>>>Gaowei (UVP); Jan Beulich; Anthony Perard; Paul Durrant
> > >>>>>Subject: Re: [Xen-devel] [PATCH v4] Hvmloader: Modify ACPI to only
> > >>>>>supply
> > >>>>>_EJ0 methods for PCIslots that support hotplug by runtime patching
> >
> > Ping...
> > Are there any news about this patch?
> 
> I think we are waiting on the patch submitter to do some homework
> and reimplement the patch based on our feedback.
> >

I' m so sorry. It's so long time.

And this work is not a top job for me right now.

Best regards,
-Gonglei

> > Thanks for any reply.
> >
> > >>>>>
> > >>>>>On Fri, 2014-05-09 at 12:00 -0400, Konrad Rzeszutek Wilk wrote:
> > >>>>>
> > >>>>>>So we could just then gat the _EJ0 functionality based on values
> > >>>>>>that
> > >>>>>>are present (or not) in the SSDT ?
> > >>>>>
> > >>>>>AIUI the very presence of _EJ0 is what marks the device as being
> > >>>>>ejectable (e.g. in the Windows device manager).
> > >>>>>
> > >>>>>It would be possible to make _EJ0 conditionally turn itself into a
> > >>>>>NOP
> > >>>>>without resorting to an SSDT, but I don't think that solves the issue
> > >>>>>they are trying to solve, which is that the user can even try to
> > >>>>>eject
> > >>>>>an non-hotplug device. (grep for UAR1 in our dsdt.asl and
> > >>>>>acpi_info->com1_present in hvmloader/acpi/build.c for an example
> > >>>>>of this
> > >>>>>sort of conditional thing)
> > >>>>>
> > >>>
> > >>>Going back to the SSDT idea. A little poking around and what not and I
> > >>>came up with something like this that I build into an SSDT:
> > >>>
> > >>>DefinitionBlock ("SSDTX.aml", "SSDT", 2, "Xen", "HVM", 0)
> > >>>{
> > >>>      /* S00 device is defined in DSDT, this allows me to
> > >>>       * refrence it in this SSDT
> > >>>       */
> > >>>      External (\_SB.PCI0.S00, DeviceObj)
> > >>>
> > >>>      ...
> > >>>
> > >>>      /* Extend the functionality of S00 */
> > >>>      Scope ( \_SB.PCI0.S00 ) {
> > >>>          Method(_EJ0, 1, NotSerialized)
> > >>>          {
> > >>>              /* Do stuffs here */
> > >>>          }
> > >>>      }
> > >>>}
> > >>
> > >>Thanks, this looks like the sort of thing I was naively imagining would
> > >>be possible.
> > >>
> > >>>So I did find some examples of this after all in my pile of ACPI
> > >>>firmware snapshots from all our supported platforms.
> > >>
> > >>Thanks (none of the machines I looked at had PCI hotplug apparently). I
> > >>was curious to know how Real Firmware Engineers(tm) dealt with this sort
> > >>of issue.
> > >>
> > >>I was worried how real life OSPMs might interpret this method being in
> > >>an SSDT instead of the DSDT. In theory it shouldn't matter, and the fact
> > >>that real firmware does this seem to suggest that at least Windows
> > >>treats it that way (which is a relief).
> > >
> > >I did actually find SSDTs that were specifically adding an _EJ0 to a
> > >device scope for a device defined externally. I attached an example from a
> > >Fujitsu system I have. The PRT1 device on SAT0 is external:
> > >
> > >External (\_SB_.PCI0.SAT0.PRT1, DeviceObj)
> > >
> > >And _EJ0 is added to the scope.
> > >
> > >>
> > >>>  I think this would
> > >>>work allowing you to just add or not add _EJ0 methods to the PCI
> > >>>devices
> > >>>you want by either using different SSDTs or doing something to generate
> > >>>or munge the SSDT at runtime (which would be simpler than messing with
> > >>>the DSDT I think.
> > >>
> > >>Without filling out the body of _EJ0 (which I tried but failed to do)
> > >>your stub compiles to 60 bytes of AML, I suppose that even having filled
> > >>in _EJ0 in the result would be less than, say, 128 bytes.
> > >>
> > >>Given that there are 32 PCI slots we would be talking about a total of
> > >>4k of space in hvmloader to provide a precompiled SSDT for each slot,
> > >>which can be inserted at runtime depending on each slots configuration.
> > >>
> > >>I wouldn't be especially surprised if the code to generate a suitable
> > >>SSDT dynamically was a reasonable proportion of that size, so unless
> > >>there is the possibility of needing other variants it seems like just
> > >>generating each of them would be the say to go.
> > >>
> > >>>  I did not try it (actually I did but ran into other
> > >>>problems on our platform :).
> > >>
> > >>;-)
> > >>
> > >>Ian.
> > >>
> > >
> > >
> >