On Mon, Jul 29, 2013 at 6:52 AM, Jeff Kirsher
<jeffrey.t.kirsher@xxxxxxxxx> wrote:
> From: Jacob Keller <jacob.e.keller@xxxxxxxxx>
>
> A PCI Express device can potentially report a link width and speed which it will
> not properly fulfill due to being plugged into a slower link higher in the
> chain. This function walks up the PCI bus chain and calculates the minimum link
> width and speed of this entire chain. This can be useful to enable a device to
> determine if it has enough bandwidth for optimum functionality.
>
> Signed-off-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
> Tested-by: Phil Schmitt <phillip.j.schmitt@xxxxxxxxx>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@xxxxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> ---
> drivers/pci/pci.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 2 ++
> 2 files changed, 45 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e37fea6..c71e78c 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3579,6 +3579,49 @@ int pcie_set_mps(struct pci_dev *dev, int mps)
> }
>
> /**
> + * pcie_get_minimum_link - determine minimum link settings of a PCI device
> + * @dev: PCI device to query
> + * @speed: storage for minimum speed
> + * @width: storage for minimum width
> + *
> + * This function will walk up the PCI device chain and determine the minimum
> + * link width and speed of the device.
> + */
> +int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
> + enum pcie_link_width *width)
> +{
> + int ret;
> +
> + *speed = PCI_SPEED_UNKNOWN;
> + *width = PCIE_LNK_WIDTH_UNKNOWN;
> +
> + while (dev) {
> + u16 lnksta;
> + enum pci_bus_speed next_speed;
> + enum pcie_link_width next_width;
> +
> + ret = pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> + if (ret)
> + return ret;
> +
> + next_speed = pcie_link_speed[lnksta & PCI_EXP_LNKSTA_CLS];
> + next_width = (lnksta & PCI_EXP_LNKSTA_NLW) >>
> + PCI_EXP_LNKSTA_NLW_SHIFT;
> +
> + if (next_speed < *speed)
> + *speed = next_speed;
> +
> + if (next_width < *width)
> + *width = next_width;
> +
> + dev = dev->bus->self;
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(pcie_get_minimum_link);
> +
> +/**
> * pci_select_bars - Make BAR mask from the type of resource
> * @dev: the PCI device for which BAR mask is made
> * @flags: resource type mask to be selected
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index fc2d1fb..38994de 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -937,6 +937,8 @@ int pcie_get_readrq(struct pci_dev *dev);
> int pcie_set_readrq(struct pci_dev *dev, int rq);
> int pcie_get_mps(struct pci_dev *dev);
> int pcie_set_mps(struct pci_dev *dev, int mps);
> +int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
> + enum pcie_link_width *width);
> int __pci_reset_function(struct pci_dev *dev);
> int __pci_reset_function_locked(struct pci_dev *dev);
> int pci_reset_function(struct pci_dev *dev);
> --
> 1.7.11.7
>
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
