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; 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 */
>>           }
>>       }
>> }
>
> 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.
>


-- 
Ross Philipson