linux-kernel - Re: [PATCH 1/1] arm: topology: parse the topology from the dt

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Message-ID: <87y2dnn3gw.mognet@arm.com>
Date:   Mon, 12 Apr 2021 12:31:59 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Ruifeng Zhang <ruifeng.zhang0110@...il.com>, linux@...linux.org.uk,
        sudeep.holla@....com, gregkh@...uxfoundation.org,
        rafael@...nel.org, a.p.zijlstra@...llo.nl,
        dietmar.eggemann@....com, mingo@...nel.org,
        ruifeng.zhang1@...soc.com, nianfu.bai@...soc.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] arm: topology: parse the topology from the dt


Hi,

On 12/04/21 15:08, Ruifeng Zhang wrote:
> From: Ruifeng Zhang <ruifeng.zhang1@...soc.com>
>
> The arm topology still parse from the MPIDR, but it is incomplete.  When
> the armv8.3 cpu runs in aarch32 mode, it will parse out the wrong topology.
>
> armv7 (A7) mpidr is:
> [11:8]      [7:2]       [1:0]
> cluster     reserved    cpu
>
> armv8.3 (A55) mpidr is:
> [23:16]     [15:8]      [7:0]
> cluster     cpu         thread
>
> For compatibility to keep the function of get capacity from default
> cputype, renamed arm parse_dt_topology to get_cputype_capacity and delete
> related logic of parse from dt.
> Arm using the same parse_dt_topology function as arm64.
>
> The arm device boot step is to look for the default cputype and get cpu
> capacity firstly. Then parse the topology and capacity from dt to replace
> default values.
>

I'm afraid I don't get it.

CONFIG_COMPAT lets you run 32-bit stuff at EL0, but the kernel is still
arm64. So if you take your armv8.3 system, the topology parsed by the
kernel will be the same regardless of CONFIG_COMPAT.

Could you elaborate on what problem you are trying to fix here?