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

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Message-ID: <72267a6c-13c7-40bd-babb-f73a28625ca4@mailbox.org>
Date: Wed, 22 Oct 2025 11:59:18 +0200
From: Stefan Roese <stefan.roese@...lbox.org>
To: "mani@...nel.org" <mani@...nel.org>
Cc: Bjorn Helgaas <helgaas@...nel.org>, "Bandi, Ravi Kumar"
 <ravib@...zon.com>,
 "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>,
 Sean Anderson <sean.anderson@...ux.dev>
Subject: Re: [PATCH v2] PCI: xilinx-xdma: Enable INTx interrupts

On 10/22/25 11:55, mani@...nel.org wrote:
> On Wed, Oct 22, 2025 at 08:59:19AM +0200, Stefan Roese wrote:
>> Hi Bjorn,
>> Hi Ravi,
>>
>> On 10/21/25 23:28, Bjorn Helgaas wrote:
>>> On Tue, Oct 21, 2025 at 08:55:41PM +0000, Bandi, Ravi Kumar wrote:
>>>>> 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
>>>>>>>> [...]
>>
>> First a comment on this IRQ logging:
>>
>> These lines do NOT refer to the INTx IRQ(s) but the controller internal
>> "events" (errors etc). Please see this log for INTx on my Versal
>> platform with pci_irqd_intx_xlate added:
>>
>>   24:          0          0  pl_dma:RC-Event   0 Level     LINK_DOWN
>>   25:          0          0  pl_dma:RC-Event   3 Level     HOT_RESET
>>   26:          0          0  pl_dma:RC-Event   8 Level     CFG_TIMEOUT
>>   27:          0          0  pl_dma:RC-Event   9 Level     CORRECTABLE
>>   28:          0          0  pl_dma:RC-Event  10 Level     NONFATAL
>>   29:          0          0  pl_dma:RC-Event  11 Level     FATAL
>>   30:          0          0  pl_dma:RC-Event  20 Level     SLV_UNSUPP
>>   31:          0          0  pl_dma:RC-Event  21 Level     SLV_UNEXP
>>   32:          0          0  pl_dma:RC-Event  22 Level     SLV_COMPL
>>   33:          0          0  pl_dma:RC-Event  23 Level     SLV_ERRP
>>   34:          0          0  pl_dma:RC-Event  24 Level     SLV_CMPABT
>>   35:          0          0  pl_dma:RC-Event  25 Level     SLV_ILLBUR
>>   36:          0          0  pl_dma:RC-Event  26 Level     MST_DECERR
>>   37:          0          0  pl_dma:RC-Event  27 Level     MST_SLVERR
>>   38:         94          0  pl_dma:RC-Event  16 Level     84000000.axi-pcie
>>   39:         94          0  pl_dma:INTx   0 Level     nvme0q0, nvme0q1
>>
>> The last line shows the INTx IRQs here ('pl_dma:INTx' vs 'pl_dma:RC-
>> Event').
>>
>> More below...
>>
>>>>>>>>
>>>>>>>> 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?
>>>>
>>>> I saw that interrupts were being generated by the endpoint device,
>>>> but I didn’t specifically check if they were correctly translated in
>>>> the controller. I noticed that the new driver wasn't explicitly
>>>> enabling the interrupts, so my first approach was to enable them,
>>>> which helped the interrupts flow through.
>>>
>>> OK, I'll assume the interrupts happened but the driver might not have
>>> been able to handle them correctly, e.g., it was prepared for INTA but
>>> got INTB or similar.
>>>
>>>>>    - 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?
>>>>
>>>> I'm not entirely sure if there are any other dependencies in the
>>>> FPGA bitstream. I'll investigate further and get back to you.
>>>
>>> Stefan clarified in a private message that he had applied your patch
>>> first, so this mystery is solved.
>>
>> Yes. I applied Ravi's patch first and still got no INTx delivered
>> to the nvme driver. That's what me triggered to dig deeper here and
>> resulted in this v2 patch with pci_irqd_intx_xlate added.
>>
>> BTW:
>> I re-tested just now w/o Ravi's patch and the INTx worked. Still I think
>> Ravi's patch is valid and should be applied...
> 
> How come INTx is working without the patch from Ravi which enabled INTx routing
> in the controller? Was it enabled by default in the hardware?

Yes, this is my best guess right now. I could double-check here, but
IMHO it makes sense to enable it "manually" as done with Ravi's patch
to not rely on this default setup at all.

Thanks,
Stefan