Date:	Thu, 08 Jan 2009 17:20:30 +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 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.
>>>
>>> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
>>> ---
>>>  drivers/pci/pcie/portdrv.h      |    1 
>>>  drivers/pci/pcie/portdrv_core.c |  155 +++++++++++++++++++++++++++++-----------
>>>  2 files changed, 117 insertions(+), 39 deletions(-)
>>>
>>> Index: linux-2.6/drivers/pci/pcie/portdrv.h
>>> ===================================================================
>>> --- linux-2.6.orig/drivers/pci/pcie/portdrv.h
>>> +++ linux-2.6/drivers/pci/pcie/portdrv.h
>>> @@ -25,6 +25,7 @@
>>>  #define PCIE_CAPABILITIES_REG		0x2
>>>  #define PCIE_SLOT_CAPABILITIES_REG	0x14
>>>  #define PCIE_PORT_DEVICE_MAXSERVICES	4
>>> +#define PORT_MSI_VECTOR_MASK		0x1f
>>>  
>>>  #define get_descriptor_id(type, service) (((type - 4) << 4) | service)
>>>  
>>> Index: linux-2.6/drivers/pci/pcie/portdrv_core.c
>>> ===================================================================
>>> --- linux-2.6.orig/drivers/pci/pcie/portdrv_core.c
>>> +++ linux-2.6/drivers/pci/pcie/portdrv_core.c
>>> @@ -30,55 +30,120 @@ static void release_pcie_device(struct d
>>>  }
>>>  
>>>  /**
>>> + * fix_up_vectors - ensure the right ordering of MSI-X interrupt vectors
>>> + * @dev: PCI Express port that is going to use the vectors
>>> + * @vectors: Array of interrupt vectors to check (2 entries)
>>> + *
>>> + * Return value:
>>> + * 0 on success, error code if the values read from config registers are not as
>>> + * expected
>>> + *
>>> + * If this function is called, we are going to use two interrupt vectors which
>>> + * may be different, but we have to make sure they are in the right order such
>>> + * that the vector to be used for PME and hotplug signalling is the first one.
>>> + *
>>> + * NOTE: The assumption here is that MSI message offset (with respect to the
>>> + * base Message Data) equal to N corresponds to index N in the array of vectors
>>> + * returned by pci_enable_msix().
>>> + */
>> I've posted the similar patch recently, which doesn't have this
>> assumption.
> 
> Actually, this assumption is in agreement with PCI Express Base Specification
> 2.0, which very clearly states in Section 7.8.2 that:
> 
> "[...] Interrupt Message Number – This field indicates which
> MSI/MSI-X vector is used for the interrupt message generated in
> association with any of the status bits of this Capability structure.
> 
> [...]
> 
> For MSI-X, the value in this field indicates which MSI-X Table
> entry is used to generate the interrupt message. The entry must
> be one of the first 32 entries even if the Function implements
> more than 32 entries. For a given MSI-X implementation, the
> entry must remain constant."
> 

Though I might be misunderstanding something, my understanding is
that this implies that there can be more MSI-X table entries than
number of interrupts, and PME/HotPlug or AER interrupts can be
mapped to other than first two entries. If my understanding is
correct, your patch would not work if PME/HotPlug or AER interrupts
were mapped to other than first two.

Regardless of my understanding is correct or not, I have another
concern. I think there are two interrupts for PCIe port service
currently as your patch indicates. But new interrupts can be added
in the future. With the assumption, PME/HotPlug and/or AER interrupts
would not work if the first several entries are mapped to other new
interrupts. Therefore, with the assumption, we need to fix MSI-X
initialization code whenever new interrupts are defined.

> Well, I have to update the comment. :-)
> 
>> Please take a look.
>>
>> http://marc.info/?l=linux-pci&m=122992792507715&w=2
> 
> OK, thanks.  I can easily change my patch to follow this behavior, although
> I don't really think it's necessary given the above.
> 

Please see above mentioned my concerns.

>> NOTE: I've confirmed MSI and INTx still work with my patch, but it
>> is not tested on the machine with MSI-X capable port, since I don't
>> have such environment.
> 
> I also have tested my patch with both MSI and INTx, but I also don't have
> MSI-X capable root ports in any of my test boxes.
> 

Though the patch is not tested with MSI-X capable ports, I think it
is much better than the current code.

Thanks,
Kenji Kaneshige



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