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SubjectRe: [PATCH v2 0/1] arm: topology: parse the topology from the dt
Date
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).

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