On -RT, TI DRA7 PCIe driver always produces below backtrace when the first PCI interrupt is triggered: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 82 at kernel/irq/handle.c:150 handle_irq_event_percpu+0x14c/0x174() irq 460 handler irq_default_primary_handler+0x0/0x14 enabled interrupts Modules linked in: ahci_platform(+) ti_vip(+) libahci_platform xhci_pci(+) c_can_platform(+) libahci xhci_hcd ti_vpe c_can libata v4l2_mem2mem can_dev gpio_keys leds_gpio snd_soc_simple_card usbcore spi_ti_qspi videobuf2_core extcon_usb_gpio omap_wdt ti_vpdma videobuf2_dma_contig ti_soc_thermal videobuf2_memops dwc3_omap extcon rtc_omap ov1063x v4l2_common videodev media snd_soc_tlv320aic3x omap_rng rng_core omap_remoteproc CPU: 1 PID: 82 Comm: irq/26-dra7-pci Not tainted 4.1.10-rt10-02638-g6486d7e-dirty #1 Hardware name: Generic DRA74X (Flattened Device Tree) Backtrace: [<c0013060>] (dump_backtrace) from [<c0013280>] (show_stack+0x18/0x1c) r7:c07acca0 r6:00000000 r5:c09034e4 r4:00000000 [<c0013268>] (show_stack) from [<c061ef14>] (dump_stack+0x90/0xac) [<c061ee84>] (dump_stack) from [<c00436e4>] (warn_slowpath_common+0x7c/0xb8) r7:c07acca0 r6:00000096 r5:00000009 r4:ee4d3e38 [<c0043668>] (warn_slowpath_common) from [<c0043758>] (warn_slowpath_fmt+0x38/0x40) r8:ee3fcc00 r7:000001cc r6:00000000 r5:00000002 r4:c07acc78 [<c0043724>] (warn_slowpath_fmt) from [<c0085fd0>] (handle_irq_event_percpu+0x14c/0x174) r3:000001cc r2:c07acc78 r4:ecfcdd80 [<c0085e84>] (handle_irq_event_percpu) from [<c008607c>] (handle_irq_event+0x84/0xb8) r10:00000001 r9:ee4b59c0 r8:ee1d0900 r7:00000001 r6:00000000 r5:ecfcdd80 r4:ee3fcc00 [<c0085ff8>] (handle_irq_event) from [<c0089240>] (handle_simple_irq+0x90/0x118) r5:ee4a9020 r4:ee3fcc00 [<c00891b0>] (handle_simple_irq) from [<c0085514>] (generic_handle_irq+0x30/0x44) r5:ee4a9020 r4:000001cc [<c00854e4>] (generic_handle_irq) from [<c034a7d4>] (dra7xx_pcie_msi_irq_handler+0x7c/0x8c) r5:ee4a9020 r4:00000001 [<c034a758>] (dra7xx_pcie_msi_irq_handler) from [<c0086f08>] (irq_forced_thread_fn+0x28/0x5c) r5:ee1d0900 r4:ee4b59c0 [<c0086ee0>] (irq_forced_thread_fn) from [<c00871dc>] (irq_thread+0x128/0x204) r7:00000001 r6:00000000 r5:ee4d2000 r4:ee4b59e4 [<c00870b4>] (irq_thread) from [<c005e2fc>] (kthread+0xd4/0xec) r10:00000000 r9:00000000 r8:00000000 r7:c00870b4 r6:ee4b59c0 r5:ee4b5a00 r4:00000000 [<c005e228>] (kthread) from [<c000faa8>] (ret_from_fork+0x14/0x2c) r7:00000000 r6:00000000 r5:c005e228 r4:ee4b5a00 ---[ end trace 0000000000000002 ]--- This backtrace is triggered because dra7xx_pcie_msi_irq_handler() forced to be threaded by default on -RT but, in the same time, it's IRQ dispatcher and calls generic_handle_irq(), which leads to handle_simple_irq() call. The handle_simple_irq() expected to be called with IRQ disabled. The same issue will also happen if kernel will boot with "threadirqs" cmdline parameter (CONFIG_IRQ_FORCED_THREADING). As discussed in [1], the current DRA7 PCIe hw configuration supports 32 interrupts, which cannot change because it's hardwired in silicon, this is a single status read and assuming that only a few (most of the time it will be exactly ONE) of those interrupts are pending at the same time is pretty much a sane assumption. And recommended fix for this issue is to request dra7xx_pcie_msi IRQ with IRQF_NO_THREAD flag. [1] https://lkml.org/lkml/2015/11/3/660 Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Grygorii Strashko <grygorii.strashko@xxxxxx> --- drivers/pci/host/pci-dra7xx.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/drivers/pci/host/pci-dra7xx.c b/drivers/pci/host/pci-dra7xx.c index 6589e7e..31460f4 100644 --- a/drivers/pci/host/pci-dra7xx.c +++ b/drivers/pci/host/pci-dra7xx.c @@ -302,8 +302,30 @@ static int __init dra7xx_add_pcie_port(struct dra7xx_pcie *dra7xx, return -EINVAL; } + /* + * Mark dra7xx_pcie_msi IRQ as IRQF_NO_THREAD + * On -RT and if kernel is booting with "threadirqs" cmd line parameter + * the dra7xx_pcie_msi_irq_handler() will be forced threaded but, + * in the same time, it's IRQ dispatcher and calls generic_handle_irq(), + * which, in turn, will be resolved to handle_simple_irq() call. + * The handle_simple_irq() expected to be called with IRQ disabled, as + * result kernle will display warning: + * "irq XXX handler YYY+0x0/0x14 enabled interrupts". + * + * Current DRA7 PCIe hw configuration supports 32 interrupts, + * which cannot change because it's hardwired in silicon, and can assume + * that only a few (most of the time it will be exactly ONE) of those + * interrupts are pending at the same time. So, It's sane way to dial + * with above issue by marking dra7xx_pcie_msi IRQ as IRQF_NO_THREAD. + * if some platform will utilize a lot of MSI IRQs and will suffer + * form -RT latencies degradation because of that - IRQF_NO_THREAD can + * be removed and "Warning Annihilation" W/A can be applied [1] + * + * [1] https://lkml.org/lkml/2015/11/2/578 + */ ret = devm_request_irq(&pdev->dev, pp->irq, - dra7xx_pcie_msi_irq_handler, IRQF_SHARED, + dra7xx_pcie_msi_irq_handler, + IRQF_SHARED | IRQF_NO_THREAD, "dra7-pcie-msi", pp); if (ret) { dev_err(&pdev->dev, "failed to request irq\n"); -- 2.6.2 -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
