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SubjectRe: [PATCH v3] PCI: Check for PCIe downtraining conditions
On Mon, Jun 4, 2018 at 6:55 PM, Alexandru Gagniuc <mr.nuke.me@gmail.com> wrote:
> PCIe downtraining happens when both the device and PCIe port are
> capable of a larger bus width or higher speed than negotiated.
> Downtraining might be indicative of other problems in the system, and
> identifying this from userspace is neither intuitive, nor straigh
> forward.
>
> The easiest way to detect this is with pcie_print_link_status(),
> since the bottleneck is usually the link that is downtrained. It's not
> a perfect solution, but it works extremely well in most cases.

Have you seen any of my comments?
For your convenience repeating below.

>
> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
> ---
>
> Changes since v2:
> - Check dev->is_virtfn flag
>
> Changes since v1:
> - Use pcie_print_link_status() instead of reimplementing logic
>
> drivers/pci/probe.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ac91b6fd0bcd..a88ec8c25dd5 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2146,6 +2146,25 @@ static struct pci_dev *pci_scan_device(struct pci_bus *bus, int devfn)
> return dev;
> }
>
> +static void pcie_check_upstream_link(struct pci_dev *dev)
> +{

> +

This is redundant blank line.

> + if (!pci_is_pcie(dev))
> + return;
> +
> + /* Look from the device up to avoid downstream ports with no devices. */
> + if ((pci_pcie_type(dev) != PCI_EXP_TYPE_ENDPOINT) &&
> + (pci_pcie_type(dev) != PCI_EXP_TYPE_LEG_END) &&
> + (pci_pcie_type(dev) != PCI_EXP_TYPE_UPSTREAM))
> + return;

I looked briefly at the use of these calls and perhaps it might make
sense to introduce
pci_is_pcie_type(dev, type) which unifies pci_is_pcie() + pci_pcie_type().

> +
> + /* Multi-function PCIe share the same link/status. */

> + if ((PCI_FUNC(dev->devfn) != 0) || dev->is_virtfn)

The one pair of parens is not needed.

> + return;
> +
> + pcie_print_link_status(dev);
> +}
> +
> static void pci_init_capabilities(struct pci_dev *dev)
> {
> /* Enhanced Allocation */
> @@ -2181,6 +2200,9 @@ static void pci_init_capabilities(struct pci_dev *dev)
> /* Advanced Error Reporting */
> pci_aer_init(dev);
>
> + /* Check link and detect downtrain errors */
> + pcie_check_upstream_link(dev);
> +
> if (pci_probe_reset_function(dev) == 0)
> dev->reset_fn = 1;
> }
> --
> 2.14.4
>



--
With Best Regards,
Andy Shevchenko

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