linux-kernel - Re: [PATCH v2] PCI: xilinx-xdma: Enable INTx interrupts

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Message-ID: <20251021191004.GA1205652@bhelgaas>
Date: Tue, 21 Oct 2025 14:10:04 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: "Bandi, Ravi Kumar" <ravib@...zon.com>
Cc: "mani@...nel.org" <mani@...nel.org>,
	"thippeswamy.havalige@....com" <thippeswamy.havalige@....com>,
	"lpieralisi@...nel.org" <lpieralisi@...nel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"kwilczynski@...nel.org" <kwilczynski@...nel.org>,
	"robh@...nel.org" <robh@...nel.org>,
	"michal.simek@....com" <michal.simek@....com>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	Stefan Roese <stefan.roese@...lbox.org>,
	Sean Anderson <sean.anderson@...ux.dev>
Subject: Re: [PATCH v2] PCI: xilinx-xdma: Enable INTx interrupts

On Tue, Oct 21, 2025 at 05:46:17PM +0000, Bandi, Ravi Kumar wrote:
> > On Oct 21, 2025, at 10:23 AM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> > On Sat, Sep 20, 2025 at 10:52:32PM +0000, Ravi Kumar Bandi wrote:
> >> The pcie-xilinx-dma-pl driver does not enable INTx interrupts
> >> after initializing the port, preventing INTx interrupts from
> >> PCIe endpoints from flowing through the Xilinx XDMA root port
> >> bridge. This issue affects kernel 6.6.0 and later versions.
> >> 
> >> This patch allows INTx interrupts generated by PCIe endpoints
> >> to flow through the root port. Tested the fix on a board with
> >> two endpoints generating INTx interrupts. Interrupts are
> >> properly detected and serviced. The /proc/interrupts output
> >> shows:
> >> 
> >> [...]
> >> 32:        320          0  pl_dma:RC-Event  16 Level     400000000.axi-pcie, azdrv
> >> 52:        470          0  pl_dma:RC-Event  16 Level     500000000.axi-pcie, azdrv
> >> [...]
> >> 
> >> Changes since v1::
> >> - Fixed commit message per reviewer's comments
> >> 
> >> Fixes: 8d786149d78c ("PCI: xilinx-xdma: Add Xilinx XDMA Root Port driver")
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Ravi Kumar Bandi <ravib@...zon.com>
> > 
> > Hi Ravi, obviously you tested this, but I don't know how to reconcile
> > this with Stefan's INTx fix at
> > https://lore.kernel.org/r/20251021154322.973640-1-stefan.roese@mailbox.org
> > 
> > Does Stefan's fix need to be squashed into this patch?
> 
> Sure, we can squash Stefan’s fix into this.

I know we *can* squash them. 

I want to know why things worked for you and Stefan when they
*weren't* squashed:

  - Why did INTx work for you even without Stefan's patch.  Did you
    get INTx interrupts but not the right ones, e.g., did the device
    signal INTA but it was received as INTB?

  - Why did Stefan's patch work for him even without your patch.  How
    could Stefan's INTx work without the CSR writes to enable
    interrupts?

  - Why you mentioned "kernel 6.6.0 and later versions."  8d786149d78c
    appeared in v6.7, so why would v6.6.0 would be affected?

> >> +++ b/drivers/pci/controller/pcie-xilinx-dma-pl.c
> >> @@ -659,6 +659,12 @@ static int xilinx_pl_dma_pcie_setup_irq(struct pl_dma_pcie *port)
> >>              return err;
> >>      }
> >> 
> >> +     /* Enable interrupts */
> >> +     pcie_write(port, XILINX_PCIE_DMA_IMR_ALL_MASK,
> >> +                XILINX_PCIE_DMA_REG_IMR);
> >> +     pcie_write(port, XILINX_PCIE_DMA_IDRN_MASK,
> >> +                XILINX_PCIE_DMA_REG_IDRN_MASK);
> >> +
> >>      return 0;
> >> }