linux-kernel - Re: [PATCH v2] PCI: Check for PCIe downtraining conditions

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Date:   Fri, 1 Jun 2018 18:12:24 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Alexandru Gagniuc <mr.nuke.me@...il.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, alex_gagniuc@...lteam.com,
        austin_bolen@...l.com, shyam_iyer@...l.com,
        Keith Busch <keith.busch@...el.com>,
        Sinan Kaya <okaya@...eaurora.org>, linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: Check for PCIe downtraining conditions

On Fri, Jun 1, 2018 at 6:01 PM, Alexandru Gagniuc <mr.nuke.me@...il.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.

> +static void pcie_check_upstream_link(struct pci_dev *dev)
> +{

> +

This is redundant, but...

> +       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;

...wouldn't be better

int type = pci_pcie_type(dev);

?

But also possible, looking at existing code,

static inline bool pci_is_pcie_type(dev, type)
{
  return pci_is_pcie(dev) ? pci_pcie_type(dev) == type : false;
}

-- 
With Best Regards,
Andy Shevchenko