linux-kernel - Re: [PATCH 1/2] PCI: pciehp: Add support for OS-First Hotplug and AER/DPC

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Message-ID: <20230515193835.GA17526@wunner.de>
Date:   Mon, 15 May 2023 21:38:35 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, oohall@...il.com,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Fontenot Nathan <Nathan.Fontenot@....com>
Subject: Re: [PATCH 1/2] PCI: pciehp: Add support for OS-First Hotplug and
 AER/DPC

On Mon, May 15, 2023 at 12:20:42PM -0700, Smita Koralahalli wrote:
> On 5/11/2023 8:23 AM, Lukas Wunner wrote:
> > Subject: [PATCH] PCI: pciehp: Disable Surprise Down Error reporting
> > 
> > On hotplug ports capable of surprise removal, Surprise Down Errors are
> > expected and no reason for AER or DPC to spring into action.  Although
> > a Surprise Down event might be caused by an error, software cannot
> > discern that from regular surprise removal.
> > 
> > Any well-behaved BIOS should mask such errors, but Smita reports a case
> > where hot-removing an Intel NVMe SSD [8086:0a54] from an AMD Root Port
> > [1022:14ab] results in irritating AER log messages and a delay of more
> > than 1 second caused by DPC handling:
[...]
> Thanks for the patch. I tested it and I notice that the AER status registers
> will still be set. I just don't see a DPC event with these settings.
> 
> I have logged in the status registers after the device is removed in
> pciehp_handle_presence_or_link_change().
[...]
> Section 6.2.3.2.2 in PCIe Spec v6.0 has also mentioned that:
> "If an individual error is masked when it is detected, its error status bit
> is still affected, but no error reporting Message is sent to the Root
> Complex, and the error is not recorded in the Header Log, TLP Prefix Log, or
> First Error Pointer"..

Thanks for the thorough testing.  So the error is logged and next time
a reporting message for a different error is sent to the Root Complex,
that earlier Surprise Down Error will be seen and you'd get belated
log messages for it, is that what you're saying?

I guess I could amend the patch to let pciehp unconditionally clear
the Surprise Down Error Status bit upon a DLLSC event.

Does the patch otherwise do what you want, i.e. no irritating messages
and no extra delay incurred by AER/DPC handling?

Thanks!

Lukas