Re: pcie hotplug driver probe is not getting called

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Oct 04, 2024 at 11:50:28PM +0530, Maverickk 78 wrote:
> The platform I am working on is rtl simulation of pcie switch(Gen6)
> with a backdoor mechanism to trigger the HotPlug event.
> 
> Tried following patches independently to have both hotplug and dpc
> driver register and handle respective events.
> 
> https://patchwork.ozlabs.org/project/linux-pci/patch/20231223212235.34293-2-mattc@purestorage.com/
> https://patchwork.kernel.org/project/linux-pci/patch/20240108194642.30460-1-mattc@purestorage.com/#25680870
> 
> Tried following
> 
> - Trigger hot removal and add, the event is triggered and respective
> msi in /proc/interrupt increments and kernel logs the event(dmesg)
> - Trigger hot removal and add, the event is triggered and respective
> msi in /proc/interrupt increments and kernel logs the event(dmesg)
> - Trigger DPC using "DPC software trigger" in DPC control register
> 
> The kernel hangs, the console is non-responsive.
> 
> Can dpc and pciehp co-exist and handle the events?

Yes, they're intended to coexist.  Your platform firmware doesn't
advertise support for it, though:

[    1.736168] acpi PNP0A08:00: _OSC: platform does not support [PCIeHotplug LTR DPC]

I don't think there's a kernel parameter to force DPC usage if the
platform doesn't advertise it.  There should be a message like "DPC:
enabled with IRQ X" if the dpc driver is active.

Even if the dpc driver isn't active, I don't think the kernel should
hang if you trigger DPC.  Since this is a QEMU guest, you should be
able to use a debugger to figure out why it's hung.

Bjorn