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

[Ruifeng Zhang]

Valentin Schneider <valentin.schneider@xxxxxxx> 于2021年4月12日周一 下午7:32写道：
>
>
> Hi,
>
> On 12/04/21 15:08, Ruifeng Zhang wrote:
> > From: Ruifeng Zhang <ruifeng.zhang1@xxxxxxxxxx>
> >
> > 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?

There is a armv8.3 cpu which should work normally both on aarch64 and aarch32.
The MPIDR has been written to the chip register in armv8.3 format.
For example,
core0: 0000000080000000
core1: 0000000080000100
core2: 0000000080000200
...

Its cpu topology can be parsed normally on aarch64 mode (both
userspace and kernel work on arm64).

The problem is when it working on aarch32 mode (both userspace and
kernel work on arm 32-bit), the cpu topology
will parse error because of the format is different between armv7 and armv8.3.
The arm 32-bit driver, arch/arm/kernel/topology will parse the MPIDR
and store to the topology with armv7,
and the result is all cpu core_id is 0, the bit[1:0] of armv7 MPIDR format.

In addition, I think arm should also allow customers to configure cpu
topologies via DT.