linux-kernel - Re: [PATCH 3/3] arm64: dts: update the cpu idle node

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Message-ID: <346ad3d2-04e4-7df3-5187-36124b3c717b@arm.com>
Date:   Thu, 15 Mar 2018 15:25:12 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ran Wang <ran.wang_1@....com>, Shawn Guo <shawnguo@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Leo Li <leoyang.li@....com>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Yuantian Tang <andy.tang@....com>
Subject: Re: [PATCH 3/3] arm64: dts: update the cpu idle node

(sorry for replying so late, just found this by accident when clearing
 old emails)

On 08/02/18 07:54, Ran Wang wrote:
> From: Yuantian Tang <andy.tang@....com>
> 
> According to PSCI standard v0.2, for CPU_SUSPEND call, which is
> used by cpu idle framework, bit[16] of state parameter must be 0.
> So update bit[16] of property 'arm,psci-suspend-param', which is
> used as state parameter, to 0.
> 
This changelog makes zero sense to me.

1. PSCI specification makes no reference to "cpu idle framework".
   It's not a Linux specification to reference anything specific to
   Linux CPUIdle framework.

2. "for CPU_SUSPEND call,...bit[16] of state parameter must be 0."
   Where exactly to you see that ? Specification tells what value of
   0 or 1 in bit[16] means.

3. Is this retention state and doesn't need any save restore ? If not
   this change is wrong and will break if and when we use
   CPU_PM_CPU_IDLE_ENTER_RETENTION if this bit is not set.

-- 
Regards,
Sudeep