Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965631AbaGPRVo (ORCPT ); Wed, 16 Jul 2014 13:21:44 -0400 Received: from mail-oa0-f51.google.com ([209.85.219.51]:52430 "EHLO mail-oa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934593AbaGPRVl (ORCPT ); Wed, 16 Jul 2014 13:21:41 -0400 MIME-Version: 1.0 In-Reply-To: <53C6761A.9090002@linaro.org> References: <1404118391-3850-1-git-send-email-daniel.thompson@linaro.org> <53C4F745.3070701@linaro.org> <201407152045.06517.marex@denx.de> <53C6761A.9090002@linaro.org> Date: Wed, 16 Jul 2014 19:21:40 +0200 Message-ID: Subject: Re: [PATCH v8 0/4] arm: KGDB NMI/FIQ support From: Harro Haan To: Daniel Thompson Cc: Marek Vasut , "linux-arm-kernel@lists.infradead.org" , linaro-kernel@lists.linaro.org, Russell King , patches@linaro.org, kgdb-bugreport@lists.sourceforge.net, Linus Walleij , Nicolas Pitre , linux-kernel@vger.kernel.org, Colin Cross , Anton Vorontsov , Ben Dooks , John Stultz , Fabio Estevam , Catalin Marinas , kernel-team@android.com, Frederic Weisbecker , Dave Martin , Detlev Zundel Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16 July 2014 14:54, Daniel Thompson wrote: > On 15/07/14 19:45, Marek Vasut wrote: >>>> 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) >> >> There's also another workaround, look at [1], but it's really a perverse hack >> thus far (blush). What I did there is I got hinted that an L1 page table can >> have this NS bit set. If this bit is set for a mapping, all accesses to memory >> area via that mapping will be non-secure. And then, in turn, by doing a non- >> secure read of the INTACK register, it will not ever happen that the FIQ number >> will pop up in the INTACK. I only do a non-secure read of the INTACK register, >> all other registers of the GICv1 are read via regular secure-mode accesses. > > I'll be looking into this approach. > > It is technically a better approach than mine since it prevents the IRQ > handler from ever reading a group 0 interrupt from INTACK. Agree, preventing the problem is better than fixing it afterwards. > > Unfortunately the tentacles of this workaround reach pretty deep in the > memory management code (rather than being concentrated in the GIC > driver) but the improved runtime behaviour might be worth it. I did some worst case measurements on the SabreSD while running: $ while true; do hackbench 20; done & Use banked non-secure GIC_CPU_INTACK register for regular interrupts (patches by Marek): The FIQ handler reads the TWD_TIMER_COUNTER 2570 ticks (which is x 1000 / 498 = 5161 nsec) after FIQ interrupt ID30 is generated. The average is around 497 ticks. The minimum is around 34 ticks. Use re-trigger approach by putting it back to pending state (latest patch by Daniel): The FIQ handler reads the TWD_TIMER_COUNTER 2678 ticks (which is x 1000 / 498 = 5378 nsec) after FIQ interrupt ID30 is generated. The average is around 563 ticks (note: almost everything is normal path) The minimum is around 34 ticks (note: this is the normal path, not the re-trigger path) So the results are quite similar. -- 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/