linux-kernel - Re: [PATCH] PCI: pciehp: Report degraded links via link bandwidth notification

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Date:   Thu, 29 Nov 2018 18:57:37 +0000
From:   <Alex_Gagniuc@...lteam.com>
To:     <helgaas@...nel.org>, <mr.nuke.me@...il.com>
Cc:     <Austin.Bolen@...l.com>, <keith.busch@...el.com>,
        <Shyam.Iyer@...l.com>, <lukas@...ner.de>,
        <mika.westerberg@...ux.intel.com>, <okaya@...eaurora.org>,
        <rafael.j.wysocki@...el.com>, <poza@...eaurora.org>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: pciehp: Report degraded links via link bandwidth
 notification

On 11/29/2018 11:36 AM, Bjorn Helgaas wrote:
> On Wed, Nov 28, 2018 at 06:08:24PM -0600, Alexandru Gagniuc wrote:
>> A warning is generated when a PCIe device is probed with a degraded
>> link, but there was no similar mechanism to warn when the link becomes
>> degraded after probing. The Link Bandwidth Notification provides this
>> mechanism.
>>
>> Use the link bandwidth notification interrupt to detect bandwidth
>> changes, and rescan the bandwidth, looking for the weakest point. This
>> is the same logic used in probe().
> 
> I like the concept of this.  What I don't like is the fact that it's
> tied to pciehp, since I don't think the concept of Link Bandwidth
> Notification is related to hotplug.  So I think we'll only notice this
> for ports that support hotplug.  Maybe it's worth doing it this way
> anyway, even if it could be generalized in the future?

That makes sense. At first, I thought that BW notification was tied to 
hotplug, but our PCIe spec writer disagreed with that assertion. I'm 
just not sure where to handle the interrupt otherwise.

Alex