Re: [PATCH RFC] pci: ACS quirk for AMD southbridge

[Andreas Hartmann]

Alex Williamson wrote:
> On Wed, 2013-06-26 at 17:14 +0200, Andreas Hartmann wrote:
>> Bjorn Helgaas wrote:
>>> [fix Joerg's email address]
>>>
>>> On Tue, Jun 25, 2013 at 10:15 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
>>>> On Wed, Jul 11, 2012 at 11:18 PM, Alex Williamson
>>>> <alex.williamson@xxxxxxxxxx> wrote:
>>>>> We've confirmed that peer-to-peer between these devices is
>>>>> not possible.  We can therefore claim that they support a
>>>>> subset of ACS.
>>>>>
>>>>> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
>>>>> Cc: Joerg Roedel <Joerg.Roedel@xxxxxxx>
>>>>> ---
>>>>>
>>>>> Two things about this patch make me a little nervous.  The
>>>>> first is that I'd really like to have a pci_is_pcie() test
>>>>> in pci_mf_no_p2p_acs_enabled(), but these devices don't
>>>>> have a PCIe capability.  That means that if there was a
>>>>> topology where these devices sit on a legacy PCI bus,
>>>>> we incorrectly return that we're ACS safe here.  That leads
>>>>> to my second problem, pciids seems to suggest that some of
>>>>> these functions have been around for a while.  Is it just
>>>>> this package that's peer-to-peer safe, or is it safe to
>>>>> assume that any previous assembly of these functions is
>>>>> also p2p safe.  Maybe we need to factor in device revs if
>>>>> that uniquely identifies this package?
>>>>>
>>>>> Looks like another useful device to potentially quirk
>>>>> would be:
>>>>>
>>>>> 00:15.0 PCI bridge: Advanced Micro Devices [AMD] nee ATI SB700/SB800/SB900 PCI to PCI bridge (PCIE port 0)
>>>>> 00:15.1 PCI bridge: Advanced Micro Devices [AMD] nee ATI SB700/SB800/SB900 PCI to PCI bridge (PCIE port 1)
>>>>> 00:15.2 PCI bridge: Advanced Micro Devices [AMD] nee ATI SB900 PCI to PCI bridge (PCIE port 2)
>>>>> 00:15.3 PCI bridge: Advanced Micro Devices [AMD] nee ATI SB900 PCI to PCI bridge (PCIE port 3)
>>>>>
>>>>> 00:15.0 0604: 1002:43a0
>>>>> 00:15.1 0604: 1002:43a1
>>>>> 00:15.2 0604: 1002:43a2
>>>>> 00:15.3 0604: 1002:43a3
>>>>>
>>>>>  drivers/pci/quirks.c |   29 +++++++++++++++++++++++++++++
>>>>>  1 file changed, 29 insertions(+)
>>>>>
>>>>> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
>>>>> index 4ebc865..2c84961 100644
>>>>> --- a/drivers/pci/quirks.c
>>>>> +++ b/drivers/pci/quirks.c
>>>>> @@ -3271,11 +3271,40 @@ struct pci_dev *pci_get_dma_source(struct pci_dev *dev)
>>>>>         return pci_dev_get(dev);
>>>>>  }
>>>>>
>>>>> +/*
>>>>> + * Multifunction devices that do not support peer-to-peer between
>>>>> + * functions can claim to support a subset of ACS.  Such devices
>>>>> + * effectively enable request redirect (RR) and completion redirect (CR)
>>>>> + * since all transactions are redirected to the upstream root complex.
>>>>> + */
>>>>> +static int pci_mf_no_p2p_acs_enabled(struct pci_dev *dev, u16 acs_flags)
>>>>> +{
>>>>> +       if (!dev->multifunction)
>>>>> +               return -ENODEV;
>>>>> +
>>>>> +       /* Filter out flags not applicable to multifunction */
>>>>> +       acs_flags &= (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC | PCI_ACS_DT);
>>>>> +
>>>>> +       return acs_flags & ~(PCI_ACS_RR | PCI_ACS_CR) ? 0 : 1;
>>>>> +}
>>>>> +
>>>>>  static const struct pci_dev_acs_enabled {
>>>>>         u16 vendor;
>>>>>         u16 device;
>>>>>         int (*acs_enabled)(struct pci_dev *dev, u16 acs_flags);
>>>>>  } pci_dev_acs_enabled[] = {
>>>>> +       /*
>>>>> +        * AMD/ATI multifunction southbridge devices.  AMD has confirmed
>>>>> +        * that peer-to-peer between these devices is not possible, so
>>>>> +        * they do support a subset of ACS even though the capability is
>>>>> +        * not exposed in config space.
>>>>> +        */
>>>>> +       { PCI_VENDOR_ID_ATI, 0x4385, pci_mf_no_p2p_acs_enabled },
>>>>> +       { PCI_VENDOR_ID_ATI, 0x439c, pci_mf_no_p2p_acs_enabled },
>>>>> +       { PCI_VENDOR_ID_ATI, 0x4383, pci_mf_no_p2p_acs_enabled },
>>>>> +       { PCI_VENDOR_ID_ATI, 0x439d, pci_mf_no_p2p_acs_enabled },
>>>>> +       { PCI_VENDOR_ID_ATI, 0x4384, pci_mf_no_p2p_acs_enabled },
>>>>> +       { PCI_VENDOR_ID_ATI, 0x4399, pci_mf_no_p2p_acs_enabled },
>>>>>         { 0 }
>>>>>  };
>>>>>
>>>>>
>>>>
>>>> I was looking for something else and found this old email.  This patch
>>>> hasn't been applied and I haven't seen any discussion about it.  Is it
>>>> still of interest?  It seems relevant to the current ACS discussion
>>>> [1].
>>
>> It is absolutely relevant. I always have to patch my kernel to get it
>> working to put my pci device to VM. Meanwhile I'm doing it for
>> kernel 3.9. I would be very glad to get these patches to the kernel as
>> they don't do anything bad!
> 
> I'd still like to see this get in too.  IIRC, where we left off was that
> Joerg had confirmed with the hardware folks that there is no
> peer-to-peer between these devices, but we still had questions about
> whether that was true for any instance of these vendor/device IDs.
> These devices are re-used in several packages and I'm not sure if we
> need to somehow figure out what package (ie. which chipset generation)
> we're looking at to know if p2p is used. 

Does this statement cover your question?
http://article.gmane.org/gmane.comp.emulators.kvm.devel/99402

Andreas
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