On Fri, May 11, 2012 at 4:56 PM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
> In a PCIe environment, transactions aren't always required to
> reach the root bus before being re-routed. Peer-to-peer DMA
> may actually not be seen by the IOMMU in these cases. For
> IOMMU groups, we want to provide IOMMU drivers a way to detect
> these restrictions. Provided with a PCI device, pci_acs_enabled
> returns the furthest downstream device with a complete PCI ACS
> chain. This information can then be used in grouping to create
> fully isolated groups. ACS chain logic extracted from libvirt.
The name "pci_acs_enabled()" sounds like it returns a boolean, but it doesn't.
I'm not sure what "a complete PCI ACS chain" means.
The function starts from "dev" and searches *upstream*, so I'm
guessing it returns the root of a subtree that must be contained in a
group.
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
>
> drivers/pci/pci.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 1 +
> 2 files changed, 44 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 111569c..d7f05ce 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2358,6 +2358,49 @@ void pci_enable_acs(struct pci_dev *dev)
> pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> }
>
> +#define PCI_EXT_CAP_ACS_ENABLED (PCI_ACS_SV | PCI_ACS_RR | \
> + PCI_ACS_CR | PCI_ACS_UF)
> +
> +/**
> + * pci_acs_enabled - test ACS support in downstream chain
> + * @dev: starting PCI device
> + *
> + * Returns the furthest downstream device with an unbroken ACS chain. If
> + * ACS is enabled throughout the chain, the returned device is the same as
> + * the one passed in.
> + */
> +struct pci_dev *pci_acs_enabled(struct pci_dev *dev)
> +{
> + struct pci_dev *acs_dev;
> + int pos;
> + u16 ctrl;
> +
> + if (!pci_is_root_bus(dev->bus))
> + acs_dev = pci_acs_enabled(dev->bus->self);
> + else
> + return dev;
> +
> + /* If the chain is already broken, pass on the device */
> + if (acs_dev != dev->bus->self)
> + return acs_dev;
> +
> + if (!pci_is_pcie(dev) || (dev->class >> 8) != PCI_CLASS_BRIDGE_PCI)
> + return dev;
> +
> + if (dev->pcie_type != PCI_EXP_TYPE_DOWNSTREAM)
> + return dev;
> +
> + pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
> + if (!pos)
> + return acs_dev;
> +
> + pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
> + if ((ctrl & PCI_EXT_CAP_ACS_ENABLED) != PCI_EXT_CAP_ACS_ENABLED)
> + return acs_dev;
> +
> + return dev;
> +}
> +
> /**
> * pci_swizzle_interrupt_pin - swizzle INTx for device behind bridge
> * @dev: the PCI device
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 9910b5c..dc25da3 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1586,6 +1586,7 @@ static inline bool pci_is_pcie(struct pci_dev *dev)
> }
>
> void pci_request_acs(void);
> +struct pci_dev *pci_acs_enabled(struct pci_dev *dev);
>
>
> #define PCI_VPD_LRDT 0x80 /* Large Resource Data Type */
>
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
