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

[Sean Anderson <sean.anderson@linux.dev>]

On 10/21/25 11:53, 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.
> 
> s/pcie-xilinx-dma-pl:/xilinx-xdma:/  # in subject
> s/has shown, that/has shown that/
> s/This patch now adds/Add/
> s/pci_irqd_intx_xlate/pci_irqd_intx_xlate()/
> 
> We'll do this when applying, no need to repost for this.
> 
> 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 think many PCI controllers just don't differentiate between legacy
interrupts. e.g. I looked at NXP's LS1046 which is based on DWC and it
does

#interrupt-cells = <1>;
interrupt-map-mask = <0 0 0 7>;
interrupt-map = <0000 0 0 1 &gic GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>,
		<0000 0 0 2 &gic GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>,
		<0000 0 0 3 &gic GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>,
		<0000 0 0 4 &gic GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>;

which I believe maps all root port legacy interrupts to a single shared
GIC interrupt. Which sort of defeats the purpose of swizzling, but most
stuff uses MSI(-X) now so I guess they figured a status register wasn't
worth the verification.

And yes, I don't think legacy interrupts are tested very much these
days.

--Sean