Re: [PATCH v2] PCI: pcie-xilinx-dma-pl: Fix off-by-one INTx IRQ handling

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Oct 21, 2025 at 06:02:40PM +0200, Stefan Roese wrote:
> On 10/21/25 17:53, Bjorn Helgaas wrote:
> > On Tue, Oct 21, 2025 at 05:43:22PM +0200, Stefan Roese wrote:
> > > While testing with NVMe drives connected to the Versal QDMA PL PCIe RP
> > > on our platform I noticed that with MSI disabled (e.g. via pci=nomsi)
> > > the NVMe interrupts are not delivered to the host CPU resulting in
> > > timeouts while probing.
> > > 
> > > Debugging has shown, that the hwirq numbers passed to this device driver
> > > (1...4, 1=INTA etc) need to get adjusted to match the numbers in the
> > > controller registers bits (0...3).
> > > 
> > > This patch now adds pci_irqd_intx_xlate to the INTx IRQ domain ops,
> > > handling this IRQ number translation correctly.
> ...

> > I wonder how many other drivers have this issue.
> > pci_irqd_intx_xlate() is used only by:
> > 
> >    dwc/pci-dra7xx.c
> >    pcie-altera.c
> >    pcie-xilinx-nwl.c
> >    pcie-xilinx.c
> >    pcie-xilinx-dma-pl.c   # this patch
> > 
> > Is there something different about these drivers that means they need
> > it when all the others don't?
> 
> I can't really tell. I'm pretty sure that this driver also needs
> pci_irqd_intx_xlate():
> 
> pcie-xilinx-cpm.c
> 
> I can't test it right now though. Perhaps in a few weeks though.
> 
> My best guess is, that legacy PCI IRQs are very rarely (not at all?)
> used and therefor tested these days. On our ZynqMP / Versal platforms this
> is currently sometimes used, as the RP does not support MSI-X
> (only MSI which is very unfortunate - and legacy of course). So it
> might be that some other drivers are missing this intx_xlate as well.
> Should be easy to test by booting with pci=nomsi.

I suspect many other drivers are also broken but not tested with INTx.
I guess we should ask about testing when merging new drivers that
claim to support INTx.