[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].
>
> If it's relevant, what's the topology? Apparently they don't have a
> PCIe capability. Is the upstream device a PCIe device (a downstream
> port or a root port)? I assume anything downstream from these AMD
> devices (0x4385, 0x439c, etc.) is plain PCI (not PCIe)?
>
> Bjorn
>
> [1] https://lkml.kernel.org/r/20130607163441.7733.23221.stgit@xxxxxxxxxx
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