Re: [PATCH] lspci: Don't report PCIe link downgrades for downstream ports

[Matthew Wilcox <willy@infradead.org>]

On Thu, Mar 18, 2021 at 12:02:44PM -0500, Bjorn Helgaas wrote:
> Drop the "downgraded" reporting for Downstream Ports.  If there is a device
> below, we'll still complain at that end if it supports a faster/wider link
> than is available.

This makes sense, but I think we should still report if training has
gone horribly wrong.  Maybe something like this ...

> +++ b/ls-caps.c
> @@ -758,13 +758,16 @@ static char *link_speed(int speed)
>      }
>  }
>  
> -static char *link_compare(int sta, int cap)
> +static char *link_compare(int type, int sta, int cap)
>  {
> +  if ((type == PCI_EXP_TYPE_ROOT_PORT) || (type == PCI_EXP_TYPE_DOWNSTREAM) ||
> +      (type == PCI_EXP_TYPE_PCIE_BRIDGE))
> +    return "";
>    if (sta < cap)
> -    return "downgraded";
> +    return " (downgraded)";
>    if (sta > cap)
> -    return "strange";
> -  return "ok";
> +    return " (strange)";
> +  return " (ok)";
>  }

{
  if (sta > cap)
    return " (overdriven)";
  if (sta == cap)
    return "";
  if ((type == PCI_EXP_TYPE_ROOT_PORT) ||
      ((type == PCI_EXP_TYPE_DOWNSTREAM) ||
      ((type == PCI_EXP_TYPE_PCIE_BRIDGE))
    return "";
  return " (downgraded)";
}

(i don't know if the PCIe spec has a better word than overdriven for this
situation, but i don't like "strange".  "invalid", maybe?)

The reason i say we should report it on the downstream port is that
we probably can't get to the config data on the upstream port/device,
so this may be our best chance to find out what's wrong.