linux-kernel - Re: [PATCH v2] cpuidle: psci: Init cpuidle only for present CPUs

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Message-ID: <20250305102542.36q7lmctx5jm4mg7@bogus>
Date: Wed, 5 Mar 2025 10:25:42 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: Yuanjie Yang <quic_yuanjiey@...cinc.com>, Jacky Bai <ping.bai@....com>
Cc: lpieralisi@...nel.org, rafael@...nel.org, daniel.lezcano@...aro.org,
	james.morse@....com, d-gole@...com, linux-pm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	imx@...ts.linux.dev, khilman@...libre.com,
	quic_tingweiz@...cinc.com
Subject: Re: [PATCH v2] cpuidle: psci: Init cpuidle only for present CPUs

Hi Jacky,

I wasn't Cc-ed on the original patch.

I was searching to provide feedback but couldn't find one.

On Wed, Mar 05, 2025 at 02:31:57PM +0800, Yuanjie Yang wrote:
> On Wed, Nov 20, 2024 at 06:37:49PM +0800, Jacky Bai wrote:
> > With 'nosmp' or 'maxcpus=0' boot command line parameters,
> > the 'cpu_present_mask' may not be the same as 'cpu_possible_mask'.
> > 
> > In current psci cpuidle driver init, for_each_possible_cpu()
> > is used to init the cpuidle for each possible CPU. but in
> > drivers/base/cpu.c ->cpu_dev_register_generic(),
> > for_each_present_cpu() is used to register cpu device for
> > present CPUs.
> > 
> > When boot system with 'nosmp' or 'maxcpus=0', the cpuidle driver
> > init failed due to no valid CPU device sysfs node for non-boot CPUs.
> > 
> > [ 0.182993] Failed to register cpuidle device for cpu1
> > 
> > Use for_each_present_cpu() to register cpuidle only for present
> > CPUs.
> > 

Can you reword it something like
"

for_each_possible_cpu() is currently used to initialize cpuidle in the
PSCI cpuidle driver.

However, in cpu_dev_register_generic(), for_each_present_cpu() is used
to register CPU devices which means the CPU devices are only registered
for present CPUs and not all possible CPUs.

With nosmp or maxcpus=0, only the boot CPU is present, leading to the
failure:

  |  Failed to register cpuidle device for cpu1

Change for_each_possible_cpu() to for_each_present_cpu() in the PSCI
cpuidle driver to ensure it only registers cpuidle devices for CPUs
that are actually present.

"

With that, you can add:

Reviewed-by: Sudeep Holla <sudeep.holla@....com>

Please cc Ulf Hansson <ulf.hansson@...aro.org> as well. Either him or
Rafael can then pick up the patch.

-- 
Regards,
Sudeep