Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758496AbaGOJlz (ORCPT ); Tue, 15 Jul 2014 05:41:55 -0400 Received: from mail-we0-f182.google.com ([74.125.82.182]:61011 "EHLO mail-we0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758450AbaGOJls (ORCPT ); Tue, 15 Jul 2014 05:41:48 -0400 Message-ID: <53C4F745.3070701@linaro.org> Date: Tue, 15 Jul 2014 10:41:25 +0100 From: Daniel Thompson User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Harro Haan CC: Russell King , linaro-kernel@lists.linaro.org, Catalin Marinas , patches@linaro.org, kgdb-bugreport@lists.sourceforge.net, Linus Walleij , Nicolas Pitre , linux-kernel@vger.kernel.org, Frederic Weisbecker , Anton Vorontsov , Ben Dooks , John Stultz , Fabio Estevam , Colin Cross , kernel-team@android.com, Dave Martin , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v8 0/4] arm: KGDB NMI/FIQ support References: <1404118391-3850-1-git-send-email-daniel.thompson@linaro.org> <1404979427-12943-1-git-send-email-daniel.thompson@linaro.org> In-Reply-To: X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/07/14 14:51, Harro Haan wrote: > On 10 July 2014 10:03, Daniel Thompson wrote: >> >> This patchset makes it possible to use kgdb's NMI infrastructure on ARM >> platforms. >> >> The patches have been previously circulated as part of a large patchset >> mixing together ARM architecture code and driver changes >> (http://thread.gmane.org/gmane.linux.ports.arm.kernel/333901 ). This >> patchset is dramatically cut down to include only the arch/arm code. The >> driver code (irqchip and tty/serial) will follow when/if the arch code >> is accepted. >> >> The first two patches modify the FIQ infrastructure to allow interrupt >> controller drivers to register callbacks (the fiq_chip structure) to >> manage FIQ routings and to ACK and EOI the FIQ. This makes it possible >> to use FIQ in multi-platform kernels and with recent ARM interrupt >> controllers. >> > > Daniel, > > Thanks for the patches. I have tested the fiq and irq-gic patches on > an i.MX6 (SabreSD board) for a different purpose: > A FIQ timer interrupt at 1 kHz. The TWD watchdog block is used in > timer mode for this (interrupt ID 30). The GIC affinity is set to CPU > core 0 only for this interrupt ID. > > I was surprised by the following behavior: > $ cat /proc/interrupts > CPU0 CPU1 CPU2 CPU3 > 29: 5459 3381 3175 3029 GIC 29 twd > 30: 11 0 0 0 GIC 30 fake-fiq > > Once every few seconds is interrupt ID 30 handled by the regular GIC > handler instead of the FIQ exception path (which causes for example a > bit more latencies). The other thousands of FIQ's are handled by the > FIQ exception path. The problem is also confirmed by the following > stackframe of the Lauterbach tooling: > fake_fiq_handler(irq = 30, ...) > handle_percpu_devid_irq(irq = 30, ...) > generic_handle_irq(irq = 30) > handle_IRQ(irq = 30, ...) > gic_handle_irq > __irq_svc > -->exception > > Notes: > - The problem will occur more often by executing the following command: > $ while true; do hackbench 20; done & > - Reading the GIC_CPU_INTACK register returns the interrupt ID of the > highest priority pending interrupt. > - The GIC_CPU_INTACK register (used by fiq_ack) will return spurious > interrupt ID 0x3FF when read in fake_fiq_handler, because > GIC_CPU_INTACK is already read by gic_handle_irq. > - The FIQ exception will not occur anymore after gic_handle_irq > read/acknowledges the FIQ by reading the GIC_CPU_INTACK register > > From the behavior above I conclude that the GIC_CPU_INTACK register is > first updated before the FIQ exception is generated, so there is a > small period of time that gic_handle_irq can read/acknowledge the FIQ. Makes sense. Avoiding this problem on GICv2 is easy (thanks to the aliased intack register) but on iMX.6 we have only a GICv1. > I can reduce the number of occurrences (not prevent it) by adding the > following hack to irq-gic.c > @@ -297,10 +309,12 @@ static asmlinkage void __exception_irq_entry > gic_handle_irq(struct pt_regs *regs > u32 irqstat, irqnr; > struct gic_chip_data *gic = &gic_data[0]; > void __iomem *cpu_base = gic_data_cpu_base(gic); > > do { > + while(readl_relaxed(gic_data_dist_base(gic) + GIC_DIST_PENDING_SET) > & (1 << 30)) > + printk(KERN_ERR "TEMP: gic_handle_irq: wait for FIQ exception\n"); > irqstat = readl_relaxed(cpu_base + GIC_CPU_INTACK); > irqnr = irqstat & ~0x1c00; I've made a more complete attempt to fix this. Could you test the following? (and be prepared to fuzz the line numbers) diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c index 73ae896..309bf2c 100644 --- a/drivers/irqchip/irq-gic.c +++ b/drivers/irqchip/irq-gic.c @@ -303,6 +303,28 @@ static int gic_set_wake(struct irq_data *d, unsigned int on) #define gic_set_wake NULL #endif +/* Check for group 0 interrupt spuriously acked as a normal IRQ. This + * workaround will only work for level triggered interrupts (and in + * its current form is actively harmful on systems that don't support + * FIQ). + */ +static u32 gic_handle_spurious_group_0(struct gic_chip_data *gic, u32 irqstat) +{ + u32 irqnr = irqstat & GICC_IAR_INT_ID_MASK; + + if (!gic_data_fiq_enable(gic) || irqnr >= 1021) + return irqnr; + + if (readl_relaxed(gic_data_dist_base(gic) + GIC_DIST_IGROUP + + (irqnr / 32 * 4)) & + BIT(irqnr % 32)) + return irqnr; + + /* this interrupt was spurious (needs to be handled as FIQ) */ + writel_relaxed(irqstat, gic_data_cpu_base(gic) + GIC_CPU_EOI); + return 1023; +} + static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs) { u32 irqstat, irqnr; @@ -310,8 +332,10 @@ static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs) void __iomem *cpu_base = gic_data_cpu_base(gic); do { + local_fiq_disable(); irqstat = readl_relaxed(cpu_base + GIC_CPU_INTACK); - irqnr = irqstat & GICC_IAR_INT_ID_MASK; + irqnr = gic_handle_spurious_group_0(gic, irqstat); + local_fiq_enable(); if (likely(irqnr > 15 && irqnr < 1021)) { irqnr = irq_find_mapping(gic->domain, irqnr); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/