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Date: Tue, 30 Apr 2024 14:29:11 +1000
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Subject: Re: [PATCH v8 12/16] arm64: psci: Ignore DENIED CPUs
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To: Jonathan Cameron <Jonathan.Cameron@huawei.com>,
 Thomas Gleixner <tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>,
 linux-pm@vger.kernel.org, loongarch@lists.linux.dev,
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 kvmarm@lists.linux.dev, x86@kernel.org, Russell King
 <linux@armlinux.org.uk>, "Rafael J . Wysocki" <rafael@kernel.org>,
 Miguel Luis <miguel.luis@oracle.com>, James Morse <james.morse@arm.com>,
 Salil Mehta <salil.mehta@huawei.com>,
 Jean-Philippe Brucker <jean-philippe@linaro.org>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 Marc Zyngier <maz@kernel.org>, Hanjun Guo <guohanjun@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
 Dave Hansen <dave.hansen@linux.intel.com>, linuxarm@huawei.com,
 justin.he@arm.com, jianyong.wu@arm.com,
 Lorenzo Pieralisi <lpieralisi@kernel.org>,
 Sudeep Holla <sudeep.holla@arm.com>
References: <20240426135126.12802-1-Jonathan.Cameron@huawei.com>
 <20240426135126.12802-13-Jonathan.Cameron@huawei.com>
From: Gavin Shan <gshan@redhat.com>
In-Reply-To: <20240426135126.12802-13-Jonathan.Cameron@huawei.com>
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On 4/26/24 23:51, Jonathan Cameron wrote:
> From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> 
> When a CPU is marked as disabled, but online capable in the MADT, PSCI
> applies some firmware policy to control when it can be brought online.
> PSCI returns DENIED to a CPU_ON request if this is not currently
> permitted. The OS can learn the current policy from the _STA enabled bit.
> 
> Handle the PSCI DENIED return code gracefully instead of printing an
> error.
> 
> Note the alternatives to the PSCI cpu_boot() callback do not
> return -EPERM so the change in smp.c has no affect.
> 
> See https://developer.arm.com/documentation/den0022/f/?lang=en page 58.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> [ morse: Rewrote commit message ]
> Signed-off-by: James Morse <james.morse@arm.com>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
> v8: Note in commit message that the -EPERM guard on the error print
>      only affects PSCI as other options never use this error code.
>      Should they do so in future, that may well indicate that they
>      now support similar refusal to boot.
> ---
>   arch/arm64/kernel/psci.c | 2 +-
>   arch/arm64/kernel/smp.c  | 3 ++-
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 

Thanks for the check and clarification that -EPERM is only sensible
to PSCI. With the clarification:

Reviewed-by: Gavin Shan <gshan@redhat.com>

Thanks,
Gavin