Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
In-Reply-To: <20180601150129.10486-1-mr.nuke.me@gmail.com>
References: <20180601150129.10486-1-mr.nuke.me@gmail.com>
From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 1 Jun 2018 18:12:24 +0300
Message-ID: <CAHp75VfzqbXmoEKE791gCPzg9Sn+Anb9evzfuocbO+F2XJVomw@mail.gmail.com>
Subject: Re: [PATCH v2] PCI: Check for PCIe downtraining conditions
To:     Alexandru Gagniuc <mr.nuke.me@gmail.com>
Cc:     Bjorn Helgaas <bhelgaas@google.com>, alex_gagniuc@dellteam.com,
        austin_bolen@dell.com, shyam_iyer@dell.com,
        Keith Busch <keith.busch@intel.com>,
        Sinan Kaya <okaya@codeaurora.org>, linux-pci@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Jun 1, 2018 at 6:01 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.

> +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