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From: Arnd Bergmann <arnd@kernel.org>
To: Mohamed Mediouni <mohamed.mediouni@caramail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Hector Martin <marcan@marcan.st>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Stan Skowronek <stan@corellium.com>
Subject: Re: [RFC PATCH 2/7] arm64: kernel: Add a WFI hook.
Date: Thu, 21 Jan 2021 12:36:27 +0100
Message-ID: <CAK8P3a0fRy8NhLJAtVpn0bH7sEgXcHJQXEJhzc7ArwTxseqLZw@mail.gmail.com> (raw)
In-Reply-To: <5403A355-A4FA-442B-8F8B-5629FCECC006@caramail.com>

On Thu, Jan 21, 2021 at 12:01 PM Mohamed Mediouni
<mohamed.mediouni@caramail.com> wrote:
> > On 21 Jan 2021, at 11:52, Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > On Wed, Jan 20, 2021 at 2:27 PM Mohamed Mediouni
> > <mohamed.mediouni@caramail.com> wrote:
> >> --- a/arch/arm64/kernel/cpu_ops.c
> >> +++ b/arch/arm64/kernel/cpu_ops.c
> >
> >> #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
> >> #include <linux/stackprotector.h>
> >> @@ -74,8 +75,14 @@ void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
> >>
> >> static void noinstr __cpu_do_idle(void)
> >> {
> >> -       dsb(sy);
> >> -       wfi();
> >> +       const struct cpu_operations *ops = get_cpu_ops(task_cpu(current));
> >> +
> >> +       if (ops->cpu_wfi) {
> >> +               ops->cpu_wfi();
> >> +       } else {
> >> +               dsb(sy);
> >> +               wfi();
> >> +       }
> >> }
> >
> > I think the correct place to put this would be a platform specific driver
> > in drivers/cpuidle/ instead of an added low-level callback in the
> > default idle function and a custom cpu_operations structure.
>
> Can we make sure that wfi never gets called even on early
> boot when using a cpuidle driver?

Good question, I don't know what all the possible call sites are
for this, but if there is nothing else works (such as what Alex suggested),
it may be possible to just patch out the wfi instruction here and
do a busy loop until the cpuidle driver has come up.

The main issue here is the existence of the custom cpu_operations
in the first place: I don't think we want or need the custom start_secondary
at the moment (as commented in the other patch), but then there is
no obvious place to put the custom wfi.

Note that there are a few other uses of the wfi instruction besides the
one in __cpu_do_idle(), so whatever you do here may also apply to the
others.

arch/arm64/include/asm/smp.h:           wfi();
arch/arm64/kernel/head.S:       wfi
arch/arm64/kernel/head.S:       wfi
arch/arm64/kernel/head.S:       wfi
arch/arm64/kernel/process.c:    wfi();
arch/arm64/kvm/hyp/nvhe/hyp-init.S:     wfi

       Arnd

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Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-20 13:27 [RFC PATCH 0/7] Linux on Apple Silicon Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 1/7] arm64: kernel: FIQ support Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 2/7] arm64: kernel: Add a WFI hook Mohamed Mediouni
2021-01-20 16:46   ` Alexander Graf
     [not found]     ` <94C20F55-D3B8-4349-B26F-9EA8AAEBF639@caramail.com>
2021-01-21 12:33       ` Hector Martin 'marcan'
2021-01-21 10:52   ` Arnd Bergmann
2021-01-21 11:01     ` Mohamed Mediouni
2021-01-21 11:36       ` Arnd Bergmann [this message]
2021-01-20 13:27 ` [RFC PATCH 3/7] arm64: mm: use nGnRnE instead of nGnRE on Apple processors Mohamed Mediouni
2021-01-20 16:47   ` Alexander Graf
2021-01-20 18:06     ` Mohamed Mediouni
2021-01-20 18:10       ` Alexander Graf
2021-01-21 11:27   ` Will Deacon
2021-01-21 11:38     ` Arnd Bergmann
2021-01-21 11:44     ` Marc Zyngier
2021-01-21 12:47       ` Will Deacon
2021-01-21 15:12         ` Mohamed Mediouni
2021-01-21 16:25           ` Marc Zyngier
2021-01-21 17:55             ` Will Deacon
2021-01-21 18:15               ` Marc Zyngier
2021-01-21 18:22                 ` Mohamed Mediouni
2021-01-21 18:22                 ` Will Deacon
2021-01-20 13:27 ` [RFC PATCH 4/7] irqchip/apple-aic: Add support for Apple AIC Mohamed Mediouni
2021-01-20 17:11   ` Alexander Graf
2021-01-20 18:04     ` Mohamed Mediouni
2021-01-20 20:16       ` Andrew Lunn
2021-01-20 21:18   ` Stan Skowronek
2021-01-21  9:48   ` Linus Walleij
2021-01-21 10:37     ` Arnd Bergmann
2021-01-21 15:29       ` Hector Martin 'marcan'
2021-01-21 17:09         ` Rob Herring
2021-01-21 17:45       ` Rob Herring
2021-01-21 16:44     ` Rob Herring
2021-01-21 16:53   ` Hector Martin 'marcan'
2021-01-20 13:27 ` [RFC PATCH 5/7] arm64/Kconfig: Add Apple Silicon SoC platform Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 6/7] arm64: kernel: Apple CPU start driver Mohamed Mediouni
2021-01-21 11:14   ` Arnd Bergmann
2021-01-20 13:27 ` [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple AIC driver Mohamed Mediouni
2021-01-21 12:44   ` Arnd Bergmann
2021-01-21 12:50     ` Mohamed Mediouni
2021-01-21 13:00       ` Arnd Bergmann
2021-01-21 13:01         ` Hector Martin 'marcan'
2021-01-21 13:22       ` Marc Zyngier
2021-01-21 13:32         ` Mark Rutland
2021-01-21 14:05           ` Marc Zyngier
2021-01-21 13:34         ` Mohamed Mediouni
2021-01-21 14:10           ` Marc Zyngier
2021-01-21 15:09             ` Arnd Bergmann
2021-01-21 15:18               ` Mohamed Mediouni
2021-01-21 16:40       ` Rob Herring
2021-01-21 16:43         ` Mohamed Mediouni
2021-01-21 17:37           ` Rob Herring
2021-01-21 18:08             ` Mohamed Mediouni
2021-01-21 18:57               ` Rob Herring
2021-02-02 19:15   ` Linus Walleij

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