Re: [PATCH v4 2/2] PCI: quirks: Fix ThunderX2 dma alias handling

[Jayachandran C <jnair@caviumnetworks.com>]

On Mon, Apr 10, 2017 at 08:28:47PM -0500, Bjorn Helgaas wrote:
> Hi Jayachandran,
> 
> On Mon, Apr 03, 2017 at 01:15:04PM +0000, Jayachandran C wrote:
> > The Cavium ThunderX2 arm64 SoCs (called Broadcom Vulcan earlier), the PCI
> > topology is slightly unusual. For a multi-node system, it looks like:
> > 
> > [node level PCI bridges - one per node]
> >     [SoC PCI devices with MSI-X but no IOMMU]
> >     [PCI-PCIe "glue" bridges - upto 14, one per real port below]
> >         [PCIe real root ports associated with IOMMU and GICv3 ITS]
> >             [External PCI devices connected to PCIe links]
> > 
> > The top two levels of bridges should have introduced aliases since they
> > are PCI and PCI/PCIe bridges, but in the case of ThunderX2 they do not.
> > In the case of external PCIe devices, the "real" root ports are connected
> > to the SMMU and the GIC ITS, so PCI-PCIe bridge does not introduce an
> > alias. The SoC PCI devices are directly connected to the GIC ITS, so the
> > node level bridges do not introduce an alias either.
> > 
> > To handle this quirk, we mark the real PCIe root ports and node level
> > PCI bridges with the flag PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT.  With this,
> > pci_for_each_dma_alias() works correctly for external PCIe devices and
> > SoC PCI devices.
> > 
> > For the current revision of Cavium ThunderX2, the VendorID and Device ID
> > are from Broadcom Vulcan (14e4:90XX).
> 
> Can you supply some text here about why we want to apply this patch?
> E.g., does it avoid making unnecessary IOMMU mappings, improve
> performance, avoid a crash, etc?

If this is for the commit message, I hope the following is ok:

"With this change, both MSI-X and IO virtualization work correctly on
Cavium ThunderX2. The GIC ITS driver gets the correct device ID to
configure MSI-X, the SMMUv3 driver gets the correct Stream IDs for PCI
devices, and the IOMMU groups are setup correctly."

I can send out a new patch if needed.

The on chip SATA and USB use MSI-X, so this is needed for basic
functionality of the platform.

> 
> > Signed-off-by: Jayachandran C <jnair@caviumnetworks.com>
> > ---
> >  drivers/pci/quirks.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 6736836..564a84a 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -3958,6 +3958,20 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x2260, quirk_mic_x200_dma_alias);
> >  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x2264, quirk_mic_x200_dma_alias);
> >  
> >  /*
> > + * The IOMMU and interrupt controller on Broadcom Vulcan/Cavium ThunderX2 are
> > + * associated not at the root bus, but at a bridge below. This quirk flag
> > + * will ensure that the aliases are identified correctly.
> > + */
> > +static void quirk_bridge_cavm_thrx2_pcie_root(struct pci_dev *pdev)
> > +{
> > +	pdev->dev_flags |= PCI_DEV_FLAGS_BRIDGE_XLATE_ROOT;
> > +}
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_BROADCOM, 0x9000,
> > +				quirk_bridge_cavm_thrx2_pcie_root);
> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_BROADCOM, 0x9084,
> > +				quirk_bridge_cavm_thrx2_pcie_root);
> > +
> > +/*
> >   * Intersil/Techwell TW686[4589]-based video capture cards have an empty (zero)
> >   * class code.  Fix it.
> >   */

Thanks,
JC.

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