From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753632AbdEISPA (ORCPT ); Tue, 9 May 2017 14:15:00 -0400 Received: from foss.arm.com ([217.140.101.70]:57936 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805AbdEISO7 (ORCPT ); Tue, 9 May 2017 14:14:59 -0400 Subject: Re: [PATCH] irq_bcm2836: Send event when onlining sleeping cores To: Eric Anholt , Phil Elwell , Thomas Gleixner , Jason Cooper , Florian Fainelli , Ray Jui , Scott Branden , bcm-kernel-feedback-list@broadcom.com, linux-kernel@vger.kernel.org, linux-rpi-kernel@lists.infradead.org References: <87ziemm0fb.fsf@eliezer.anholt.net> <1e871525-3298-f16d-4f95-a44bc78068b5@arm.com> <87o9v1c37r.fsf@eliezer.anholt.net> From: Marc Zyngier Organization: ARM Ltd Message-ID: <7f6f5e05-07b1-e64d-401c-a189623c22a0@arm.com> Date: Tue, 9 May 2017 19:14:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <87o9v1c37r.fsf@eliezer.anholt.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/17 19:08, Eric Anholt wrote: > Marc Zyngier writes: > >> On 09/05/17 17:59, Eric Anholt wrote: >>> Phil Elwell writes: >>> >>>> In order to reduce power consumption and bus traffic, it is sensible >>>> for secondary cores to enter a low-power idle state when waiting to >>>> be started. The wfe instruction causes a core to wait until an event >>>> or interrupt arrives before continuing to the next instruction. >>>> The sev instruction sends a wakeup event to the other cores, so call >>>> it from bcm2836_smp_boot_secondary, the function that wakes up the >>>> waiting cores during booting. >>>> >>>> It is harmless to use this patch without the corresponding change >>>> adding wfe to the ARMv7/ARMv8-32 stubs, but if the stubs are updated >>>> and this patch is not applied then the other cores will sleep forever. >>>> >>>> See: https://github.com/raspberrypi/linux/issues/1989 >>>> >>>> Signed-off-by: Phil Elwell >>>> --- >>>> drivers/irqchip/irq-bcm2836.c | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/drivers/irqchip/irq-bcm2836.c b/drivers/irqchip/irq-bcm2836.c >>>> index e10597c..6dccdf9 100644 >>>> --- a/drivers/irqchip/irq-bcm2836.c >>>> +++ b/drivers/irqchip/irq-bcm2836.c >>>> @@ -248,6 +248,9 @@ static int __init bcm2836_smp_boot_secondary(unsigned int cpu, >>>> writel(secondary_startup_phys, >>>> intc.base + LOCAL_MAILBOX3_SET0 + 16 * cpu); >>>> >>>> + dsb(sy); /* Ensure write has completed before waking the other CPUs */ >>>> + sev(); >>>> + >>>> return 0; >>>> } >>> >>> This is also the behavior that the standard arm64 spin-table method has, >>> which we unfortunately can't quite use. >> >> And why is that so? Why do you have to reinvent the wheel (and hide the >> cloned wheel in an interrupt controller driver)? >> >> That doesn't seem right to me. > > The armv8 stubs (firmware-supplied code in the low page that do the > spinning) do actually implement arm64's spin-table method. It's the > armv7 stubs that use these registers in the irqchip instead of plain > addresses in system memory. Let's put ARMv7 aside for the time being. If your firmware already implements spin-tables, why don't you simply use that at least on arm64? Thanks, M. -- Jazz is not dead. It just smells funny...