linux-kernel - Re: [PATCH v4 1/3] PCI: pciehp: Add support for async hotplug with native AER and DPC/EDR

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Date:   Mon, 28 Aug 2023 09:35:42 +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>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Yazen Ghannam <yazen.ghannam@....com>
Subject: Re: [PATCH v4 1/3] PCI: pciehp: Add support for async hotplug with
 native AER and DPC/EDR

On Tue, Aug 15, 2023 at 09:20:41PM +0000, Smita Koralahalli wrote:
> According to PCIe r6.0 sec 6.7.6 [1], async removal with DPC may result in
> surprise down error. This error is expected and is just a side-effect of
> async remove.
> 
> Add support to handle the surprise down error generated as a side-effect
> of async remove. Typically, this error is benign as the pciehp handler
> invoked by PDC or/and DLLSC alongside DPC, de-enumerates and brings down
> the device appropriately. But the error messages might confuse users. Get
> rid of these irritating log messages with a 1s delay while pciehp waits
> for dpc recovery.
[...]
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>

Reviewed-by: Lukas Wunner <lukas@...ner.de>

The subject is slightly inaccurate as this doesn't touch pciehp source
files, although it is *related* to pciehp.

As an example, a perhaps more accurate subject might be something like...

  PCI/DPC: Ignore Surprise Down errors on hot removal

...but I don't think it's necessary to respin just for that as Bjorn is
probably able to adjust the subject to his liking when applying the patch.

Thanks a lot for patiently pursuing this issue, good to see it fixed.

Five years ago there was an attempt to solve it through masking Surprise
Down errors, which you've verified to not be a viable approach:

https://patchwork.kernel.org/project/linux-pci/patch/20180818065126.77912-2-okaya@kernel.org/

Lukas