linux-kernel - Re: [PATCH v2 2/2] ACPI: processor: idle: Replace single idle driver with per-CPU model for better hybrid CPU support

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Message-ID: <CAJZ5v0hGj3=GxnLkj0adm+ENSk7YbzNZRPiBTgm_bKZsH3OYDw@mail.gmail.com>
Date: Mon, 25 Aug 2025 16:56:57 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Yaxiong Tian <tianyaxiong@...inos.cn>
Cc: rafael@...nel.org, daniel.lezcano@...aro.org, lenb@...nel.org, 
	robert.moore@...el.com, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org, 
	acpica-devel@...ts.linux.dev, Shaobo Huang <huangshaobo2075@...tium.com.cn>, 
	Yinfeng Wang <wangyinfeng@...tium.com.cn>, Xu Wang <wangxu@...tium.com.cn>
Subject: Re: [PATCH v2 2/2] ACPI: processor: idle: Replace single idle driver
 with per-CPU model for better hybrid CPU support

On Thu, Aug 14, 2025 at 9:32 AM Yaxiong Tian <tianyaxiong@...inos.cn> wrote:
>
> Current implementations of hybrid architectures (e.g., ARM64 big.LITTLE
> and Intel Alder Lake) feature CPU cores with different exit latencies.

This is not true for Intel platforms, all of the CPUs in there have
the same set of C-states.

> Using a single driver to describe_LPI states for all core types is
> therefore suboptimal. This is further supported by ACPI specification
> 8.4.4.1 which states: "In a processor hierarchy, each node has its
> own _LPI low-power states specific to that node."
>
> To address these limitations, we replace the monolithic idle driver

It cannot be replaced or you potentially open a Pandora's box of
regressions on old systems in the field.

> with a per-CPU model. This approach enables accurate idle state representation
> for each core type

The per-CPU model can be used instead of the "monolithic idle driver"
only if the platform is actually known to be hybrid.

> Tested-by: Shaobo Huang <huangshaobo2075@...tium.com.cn>
> Signed-off-by: Yaxiong Tian <tianyaxiong@...inos.cn>
> Signed-off-by: Shaobo Huang <huangshaobo2075@...tium.com.cn>
> Signed-off-by: Yinfeng Wang <wangyinfeng@...tium.com.cn>
> Signed-off-by: Xu Wang<wangxu@...tium.com.cn>

What do all of the above S-o-b mean?  Are these people involved in the
development of the code?  In that case Co-developed-by is also needed.

Thanks!