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From: Hector Martin 'marcan' <marcan@marcan.st>
To: Mohamed Mediouni <mohamed.mediouni@caramail.com>,
	Alexander Graf <graf@amazon.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
	Will Deacon <will@kernel.org>,
	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 21:33:46 +0900
Message-ID: <ed4a0329-c623-f8ea-9cb1-3e11a22344f4@marcan.st> (raw)
In-Reply-To: <94C20F55-D3B8-4349-B26F-9EA8AAEBF639@caramail.com>

I already mentioned this privately, but for the benefit of the ML:

On 21/01/2021 09.48, Mohamed Mediouni wrote:
> If we explicitly use the hardware override registers for this, then
> we'll be unable to use the deep sleep support provided by wfi on
> Apple SoCs later on without touching Apple-specific MSRs.
> 
> Our current policy is to avoid having those modified inside the kernel
> at all costs, considering it to be a job for the bootloader instead.

I don't think there is any particular reason to do this; the bootloader 
should be responsible for setting up all the chicken bits that make the 
CPU work properly, including doing so for all SMP cores before entering 
the kernel, but that's not the same thing as power management bits.

It seems entirely reasonable to me to configure WFI as clockgate only 
(so it keeps state), not touch this part of kernel code at all, and then 
in the cpuidle driver (which can come later) just do:

- switch to powerdown mode
- save state
- wfi
- restore state
- switch to clockgate mode

-- 
Hector Martin "marcan" (marcan@marcan.st)
Public Key: https://mrcn.st/pub

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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' [this message]
2021-01-21 10:52   ` Arnd Bergmann
2021-01-21 11:01     ` Mohamed Mediouni
2021-01-21 11:36       ` Arnd Bergmann
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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