linux-kernel - Re: [PATCH 5/8] PCI PCIe portdrv: Fix allocation of interrupts

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Date:	Tue, 13 Jan 2009 11:47:41 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] PCI PCIe portdrv: Fix allocation of interrupts

Rafael J. Wysocki wrote:
> On Saturday 10 January 2009, Jesse Barnes wrote:
>> On Thursday, January 8, 2009 12:45 pm Rafael J. Wysocki wrote:
>>> On Thursday 08 January 2009, Rafael J. Wysocki wrote:
>>>> On Thursday 08 January 2009, Kenji Kaneshige wrote:
>>>>> Rafael J. Wysocki wrote:
>>>>>> On Thursday 08 January 2009, Kenji Kaneshige wrote:
>>>>>>> Rafael J. Wysocki wrote:
>>>>>>>> From: Rafael J. Wysocki <rjw@...k.pl>
>>>>>>>>
>>>>>>>> If MSI-X interrupt mode is used by the PCI Express port driver, too
>>>>>>>> many vectors are allocated and it is not ensured that the right
>>>>>>>> vectors will be used for various services.  Namely, the PCI Express
>>>>>>>> specification states that both PCI Express native PME and PCI
>>>>>>>> Express hotplug will always use the same MSI or MSI-X message for
>>>>>>>> signalling interrupts, which implies that the same vector will be
>>>>>>>> used by both of them.  Also, the VC service does not use interrupts
>>>>>>>> at all. Moreover, is not clear which of the vectors allocated by
>>>>>>>> pci_enable_msix() will be used for PME and hotplug and which of
>>>>>>>> them will be used for AER if all of these services are configured.
>>>>>>>>
>>>>>>>> For these reasons, rework the allocation of interrupts for PCI
>>>>>>>> Express ports so that at most two vectors are allocated and ensure
>>>>>>>> that the right vector will be used for the right purpose.
>>> Appended is a cleaned-up version of the patch that also contains comments
>>> with references to the appropriate sections of the PCI Express spec.
>> We'll need testing here in any case; I'll have to re-read the specs carefully 
>> to see if we can really rely on the vector numbers you have here (at first 
>> glance Kenji-san's approach seems more robust).
> 
> It has a catch too.  Namely, is there any warranty that we'll get the same
> vectors when the second pci_enable_msix() is called and that they will be in
> the same order?
> 

In my understanding, the following description of Interrupt Message
Number in the PCI Express spec explains this.

"[...] For a given MSI-X implementation, the entry must remain constant. [...]"

Thanks,
Kenji Kaneshige


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