Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754106AbaA0RhF (ORCPT ); Mon, 27 Jan 2014 12:37:05 -0500 Received: from mail-qa0-f43.google.com ([209.85.216.43]:53873 "EHLO mail-qa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754000AbaA0RhB (ORCPT ); Mon, 27 Jan 2014 12:37:01 -0500 Date: Mon, 27 Jan 2014 12:36:59 -0500 (EST) From: Nicolas Pitre To: Russell King - ARM Linux cc: Catalin Marinas , Benjamin Herrenschmidt , Paul Mundt , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , "Rafael J. Wysocki" , Daniel Lezcano , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org, linux-pm@vger.kernel.org, linaro-kernel@lists.linaro.org Subject: Re: [PATCH 1/9] ARM: get rid of arch_cpu_idle_prepare() In-Reply-To: <20140127160654.GO15937@n2100.arm.linux.org.uk> Message-ID: References: <1390802904-28399-1-git-send-email-nicolas.pitre@linaro.org> <1390802904-28399-2-git-send-email-nicolas.pitre@linaro.org> <20140127124511.GK15937@n2100.arm.linux.org.uk> <20140127160654.GO15937@n2100.arm.linux.org.uk> User-Agent: Alpine 2.11 (LFD 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 27 Jan 2014, Russell King - ARM Linux wrote: > On Mon, Jan 27, 2014 at 10:45:59AM -0500, Nicolas Pitre wrote: > > On Mon, 27 Jan 2014, Russell King - ARM Linux wrote: > > > > > On Mon, Jan 27, 2014 at 01:08:16AM -0500, Nicolas Pitre wrote: > > > > ARM and ARM64 are the only two architectures implementing > > > > arch_cpu_idle_prepare() simply to call local_fiq_enable(). > > > > > > > > We have secondary_start_kernel() already calling local_fiq_enable() and > > > > this is done a second time in arch_cpu_idle_prepare() in that case. And > > > > enabling FIQs has nothing to do with idling the CPU to start with. > > > > > > > > So let's introduce init_fiq_boot_cpu() to take care of FIQs on the boot > > > > CPU and remove arch_cpu_idle_prepare(). This is now done a bit earlier > > > > at late_initcall time but this shouldn't make a difference in practice > > > > i.e. when FIQs are actually used. > > > > > > > > Signed-off-by: Nicolas Pitre > > > > --- > > > > arch/arm/kernel/process.c | 5 ----- > > > > arch/arm/kernel/setup.c | 7 +++++++ > > > > 2 files changed, 7 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c > > > > index 92f7b15dd2..725b8c95e0 100644 > > > > --- a/arch/arm/kernel/process.c > > > > +++ b/arch/arm/kernel/process.c > > > > @@ -142,11 +142,6 @@ static void default_idle(void) > > > > local_irq_enable(); > > > > } > > > > > > > > -void arch_cpu_idle_prepare(void) > > > > -{ > > > > - local_fiq_enable(); > > > > -} > > > > - > > > > void arch_cpu_idle_enter(void) > > > > { > > > > ledtrig_cpu(CPU_LED_IDLE_START); > > > > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c > > > > index 987a7f5bce..d027b1a6fe 100644 > > > > --- a/arch/arm/kernel/setup.c > > > > +++ b/arch/arm/kernel/setup.c > > > > @@ -789,6 +789,13 @@ static int __init init_machine_late(void) > > > > } > > > > late_initcall(init_machine_late); > > > > > > > > +static int __init init_fiq_boot_cpu(void) > > > > +{ > > > > + local_fiq_enable(); > > > > + return 0; > > > > +} > > > > +late_initcall(init_fiq_boot_cpu); > > > > > > arch_cpu_idle_prepare() gets called from the swapper thread, and changes > > > the swapper thread's CPSR. init_fiq_boot_cpu() gets called from PID1, the > > > init thread, and changes the init thread's CPSR, which will already have > > > FIQs enabled by way of how kernel threads are created. > > > > > > Hence, the above code fragment has no effect what so ever, and those > > > platforms using FIQs will not have FIQs delivered if they're idle > > > (because the swapper will have FIQs masked at the CPU.) > > > > You're right. > > > > What about moving local_fiq_enable() to trap_init() then? > > That's potentially unsafe, as we haven't touched any of the IRQ > controllers at that point - we can't guarantee what state they'd be > in. Given that the default FIQ is to just return, a FIQ being raised > at that point will end up with an infinite loop re-entering the FIQ > handler. Okay... I don't see any obvious way to work around that besides adding another explicit hook, which arch_cpu_idle_prepare() incidentally already is. So, unless you have a better idea, I'll drop this patch and leave ARM as the only user of arch_cpu_idle_prepare(). Nicolas -- 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/