Re: [PATCH -v6 2/2] IPMI: use ACPI detection mechanism firstly to detect IPMI system interface

[Myron Stowe <myron.stowe@hp.com>]

On Tue, 2010-06-08 at 13:10 +0800, ykzhao wrote:
> On Tue, 2010-06-08 at 09:34 +0800, Matthew Garrett wrote:
> > On Tue, Jun 08, 2010 at 09:28:51AM +0800, ykzhao wrote:
> > 
> > > Does there exist the ACPI detection mechanism on the machines you
> > > mentioned? If exists, does it detect the same IPMI interface with the
> > > PCI IPMI detection mechanism?
> > 
> > What is "the same"? It's not using the same ioport space, certainly.
> 
> "The same" means that they will use the same ioport space/address.
> If they use the different ioport space/address, they will be regarded as
> the different IPMI device.
ACPI namespace* should not be enumerating a device that is discoverable
via standard PCI device enumeration so if there are multiple IPMI
devices in a system, where one is enumerated via ACPI namespace and
another is enumerated via PCI they should never be "the same" literal
device.

* I specifically denoted namespace since the ACPI SPMI table, yet
another ACPI based IPMI enumeration mechanism, seems as if it could
denote "the same" literal device.


Matthew's approach, giving a PCI based IPMI device precedence due to its
inclusion of interrupt information, does seem to have merit.

Myron
> 
> > 
> > > If the two mechanisms will detect the same IPMI interface, I agree with
> > > what you are concerned.  Do you have an idea/thought to set up the
> > > relationship between ACPI and IPMI interface? In order to enable that
> > > AML code can access the IPMI, it should know which IPMI interface will
> > > be accessed and create the corresponding user interface. If ACPI
> > > mechanism will fail to register the IPMI interface, maybe it is
> > > difficult to create the correct user interface.
> > 
> > Well, right now if you change the ordering then the PCI interface will 
> > never be exposed. It would be preferable to only expose the ACPI 
> > interface as a user-visible device if there's no prior device - if there 
> > is, I think the ideal solution would be for it to be an in-kernel only 
> > device without a corresponding UI.
> 
> Sorry that I don't explain it clearly. The concept of "user interface"
> in IPMI interface is only a channel that can be used to communicate with
> the IPMI controller. It has no relationship with whether the IPMI
> interface should be exposed to user space. If one driver wants to
> communicate with one IPMI interface, we should create one "user
> interface" firstly and send the corresponding IPMI message by using the
> "user interface".
> 
> If one IPMI interface(controller) is already detected by PCI mechanism,
> then ACPI will fail to detect the same IPMI interface. In such case it
> is difficult for ACPI to know which IPMI interface should be accessed
> when the ACPI AML code need to communicate with the IPMI interface.
> 
> thanks
>    Yakui
> 
> > 
> 


-- 
Myron Stowe                             HP Open Source Linux Lab (OSLL)

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