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

[Paul Durrant]

> -----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
> 
> 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)
> 

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