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SubjectRe: [PATCH v2 0/1] arm: topology: parse the topology from the dt
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On 15/04/2021 20:09, Valentin Schneider wrote:
> On 14/04/21 20:23, Ruifeng Zhang wrote:
>> From: Ruifeng Zhang <ruifeng.zhang1@unisoc.com>
>>
>> In Unisoc, the sc9863a SoC which using cortex-a55, it has two software
>> version, one of them is the kernel running on EL1 using aarch32.
>> user(EL0) kernel(EL1)
>> sc9863a_go aarch32 aarch32
>> sc9863a aarch64 aarch64
>>
>> When kernel runs on EL1 using aarch32, the topology will parse wrong.
>> For example,
>> The MPIDR has been written to the chip register in armv8.2 format.
>> For example,
>> core0: 0000000080000000
>> core1: 0000000080000100
>> core2: 0000000080000200
>> ...
>>
>> It will parse to:
>> | | aff2 | packageid | coreid |
>> |-------+------+-----------+--------|
>> | Core0 | 0 | 0 | 0 |
>> | Core1 | 0 | 1 | 0 |
>> | Core2 | 0 | 2 | 0 |
>> | ... | | | |
>>
>> The wrong topology is that all of the coreid are 0 and unexpected
>> packageid.
>>
>> The reason is the MPIDR format is different between armv7 and armv8.2.
>> armv7 (A7) mpidr is:
>> [11:8] [7:2] [1:0]
>> cluster reserved cpu
>> The cortex-a7 spec DDI0464F 4.3.5
>> https://developer.arm.com/documentation/ddi0464/f/?lang=en
>>
>> armv8.2 (A55) mpidr is:
>> [23:16] [15:8] [7:0]
>> cluster cpu thread
>>
>
> What I had understood from our conversation was that there *isn't* a format
> difference (at least for the bottom 32 bits) - arm64/kernel/topopology.c
> would parse it the same, except that MPIDR parsing has been deprecated for
> arm64.
>
> The problem is that those MPIDR values don't match the actual topology. If
> they had the MT bit set, i.e.
>
> core0: 0000000081000000
> core1: 0000000081000100
> core2: 0000000081000200
>
> then it would be parsed as:
>
> | | package_id | core_id | thread_id |
> |-------+------------+---------+-----------|
> | Core0 | 0 | 0 | 0 |
> | Core1 | 0 | 1 | 0 |
> | Core2 | 0 | 2 | 0 |
>
> which would make more sense (wrt the actual, physical topology).

... and this would be in sync with
https://developer.arm.com/documentation/100442/0200/register-descriptions/aarch32-system-registers/mpidr--multiprocessor-affinity-register

MT, [24]

0b1 ...

There is no 0b0 for MT.

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