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

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Date:	Tue, 25 Jun 2013 22:22:00 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	andihartmann@...19freenet.de,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH RFC] pci: ACS quirk for AMD southbridge

[fix Joerg's email address]

On Tue, Jun 25, 2013 at 10:15 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Wed, Jul 11, 2012 at 11:18 PM, Alex Williamson
> <alex.williamson@...hat.com> 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@...hat.com>
>> Cc: Joerg Roedel <Joerg.Roedel@....com>
>> ---
>>
>> 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@bling.home
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