Re: [PATCH 0/2] Ignore spurious PCIe hotplug events

[Lukas Wunner <lukas@wunner.de>]

On Tue, Apr 15, 2025 at 02:51:42PM -0600, Keith Busch wrote:
> On Thu, Apr 10, 2025 at 05:27:10PM +0200, Lukas Wunner wrote:
> > First of all, PCIe hotplug is deliberately ignoring link events occurring
> > as a side effect of Downstream Port Containment.  But it's not yet ignoring
> > Presence Detect Changed events.  These can happen if a hotplug bridge uses
> > in-band presence detect.  Reported by Keith Busch, patch [1/2] seeks to
> > fix it.
> 
> There are switches that let you
> toggle downstream connections to change what's attached and it causes a
> DPC event, swapping out the downstream device at the same time. So this
> change has the pci driver resume with the wrong device if you happen to
> be in such a situation. I don't have such switches anymore

What's the error type causing the DPC event?  Surprise Down?

Since commit 2ae8fbbe1cd4 ("PCI/DPC: Ignore Surprise Down error on hot
removal"), which went into v6.9, the DPC driver handles Surprise Down
silently and it tells the hotplug driver *not* to ignore the hotplug
event.  It does that by unconditionally clearing the PCI_DPC_RECOVERED
flag at the end of dpc_handle_surprise_removal().

Hence in the situation you're describing, the hotplug driver should
always bring down the slot and bring it back up with the new device.

Thanks,

Lukas