Hello, I installed centos8 , and I use uio_pci_generic, in order to communicate with FPGA (Xilinx) through PCIe in userspace. The cpu is ATOM cpu. I first install the driver: echo "10ee 0007" > /sys/bus/pci/drivers/uio_pci_generic/new_id I use userspace application which wait for interrupt, just as described in code example here: https://www.kernel.org/doc/html/v4.1...uio-howto.html I than trigger an interrupt from FPGA, but no print from the userspace application is given and there is an exception: irq 23: nobody cared (try booting with the "irqpoll" option) [ 91.030760] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.18.16 #6 [ 91.037037] Hardware name: /conga-MA5, BIOS MA50R000 10/30/2019 [ 91.043302] Call Trace: [ 91.045881] <IRQ> [ 91.048002] dump_stack+0x5c/0x80 [ 91.051464] __report_bad_irq+0x35/0xaf [ 91.055465] note_interrupt.cold.9+0xa/0x63 [ 91.059823] handle_irq_event_percpu+0x68/0x70 [ 91.064470] handle_irq_event+0x37/0x57 [ 91.068481] handle_fasteoi_irq+0x97/0x150 [ 91.072758] handle_irq+0x1a/0x30 [ 91.076230] do_IRQ+0x44/0xd0 [ 91.079333] common_interrupt+0xf/0xf [ 91.083154] </IRQ> [ 91.085360] RIP: 0010:cpuidle_enter_state+0x7d/0x220 [ 91.090563] Code: e8 18 1a 45 00 41 89 c4 e8 d0 50 b1 ff 65 8b 3d d9 db e5 5f e8 44 4f b1 ff 31 ff 48 89 c3 e8 ea 61 b1 ff fb 66 0f 1f 44 00 00 <48> b8 ff ff ff ff f3 01 00 00 4c 29 eb ba ff ff ff 7f 48 89 d9 48 [ 91.110283] RSP: 0018:ffffb20e806b7ea8 EFLAGS: 00000286 ORIG_RAX: ffffffffffffffda [ 91.118203] RAX: ffff90133fd214c0 RBX: 00000015316faa09 RCX: 000000000000001f [ 91.125662] RDX: 00000015316faa09 RSI: 0000000000000000 RDI: 0000000000000000 [ 91.133133] RBP: ffff90133fd2b300 R08: 0000011741eb842c R09: 0000000000000006 [ 91.140605] R10: 00000000ffffffff R11: ffff90133fd205a8 R12: 0000000000000001 [ 91.148068] R13: 00000015316f98b9 R14: 0000000000000001 R15: 0000000000000000 [ 91.155523] ? cpuidle_enter_state+0x76/0x220 [ 91.160088] do_idle+0x221/0x260 [ 91.163470] cpu_startup_entry+0x6a/0x70 [ 91.167588] start_secondary+0x1a4/0x1f0 [ 91.171676] secondary_startup_64+0xb7/0xc0 [ 91.176043] handlers: [ 91.178419] [<00000000ec05b056>] uio_interrupt [ 91.183054] Disabling IRQ #23 So, I started debugging this issue in kernel uio_pci_generic.c code, and according to the prints below, it seems that irq is catched but not delivered to userspace: static irqreturn_t irqhandler(int irq, struct uio_info *info) { struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info); printk("i'm here 1\n"); <<--- this is printed if (!pci_check_and_mask_intx(gdev->pdev)) return IRQ_NONE; printk("i'm here 2\n"); <<--- but this is NOT printed /* UIO core will signal the user process. */ return IRQ_HANDLED; } Reading documentation, I see that pci_check_and_mask_intx is actually checking if interrupt bit is set in configuration space. Since it seems to return 0 ,it should mean that it finds that this bit is not enabled. But how can it be that irq is triggered and status bit is not enabled in configuration space ? The device appear as following with lspci -vv: 02:00.0 RAM memory: Xilinx Corporation Default PCIe endpoint ID Subsystem: Xilinx Corporation Default PCIe endpoint ID Control: I/O- Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx- Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx- Interrupt: pin A routed to IRQ 23 Region 0: Memory at 91200000 (32-bit, non-prefetchable) [size=1M] Capabilities: [40] Power Management version 3 Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-) Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME- Capabilities: [48] MSI: Enable- Count=1/1 Maskable- 64bit+ Address: 0000000000000000 Data: 0000 Capabilities: [58] Express (v1) Endpoint, MSI 00 DevCap: MaxPayload 256 bytes, PhantFunc 1, Latency L0s <64ns, L1 <1us ExtTag+ AttnBtn- AttnInd- PwrInd- RBE+ FLReset- SlotPowerLimit 10.000W DevCtl: Report errors: Correctable- Non-Fatal- Fatal- Unsupported- RlxdOrd+ ExtTag+ PhantFunc- AuxPwr- NoSnoop+ MaxPayload 256 bytes, MaxReadReq 512 bytes DevSta: CorrErr- UncorrErr- FatalErr- UnsuppReq- AuxPwr- TransPend- LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s, Exit Latency L0s unlimited ClockPM- Surprise- LLActRep- BwNot- ASPMOptComp- LnkCtl: ASPM Disabled; RCB 64 bytes Disabled- CommClk+ ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt- LnkSta: Speed 2.5GT/s, Width x1, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt- Capabilities: [100 v1] Device Serial Number 00-00-00-00-00-00-00-00 Kernel driver in use: uio_pci_generic I also verified that there are no additional irq numbered 23 except for our device. How can it be that irq is catched, but not delivered to userspace ? Thank you for any idea, ranran