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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, May 09, 2014 at 01:32:58PM -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; kevin@koconnor.net; Huangweidong (C); Hanweidong
> >>(Randy); mst@redhat.com; qemu-devel@nongnu.org; xen-
> >>devel@lists.xen.org; fabio.fantoni@m2r.biz;
> >>johannes.krampf@googlemail.com; 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
> >>
> >>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 */
>         }
>     }
> }

Oh nice. That certainly would be neater then my idea.

> 
> So I did find some examples of this after all in my pile of ACPI firmware
> snapshots from all our supported platforms. 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.
> I did not try it (actually I did but ran into other problems on our platform
> :).

:-)

> 
> >
> >Yes, ejectable is only part of it. If there's appropriate AML for the slot, it is enough to indicate that a device is removable. I found the following link to an old M$ doc describing hotplug PCI: http://www.microsoft.com/china/whdc/system/pnppwr/hotadd/hotplugpci.mspx. (There's a load of Chinese characters surrounding the doc, but the body is in English).
> >
> >   Paul
> >
> >-----
> >No virus found in this message.
> >Checked by AVG - www.avg.com
> >Version: 2014.0.4570 / Virus Database: 3931/7443 - Release Date: 05/05/14
> >
> 
> 
> -- 
> Ross Philipson