Need suggestions for smp related properties in cpus.yaml to support smpboot for cortex-r52 based platform

[Ayan Kumar Halder]

Hi Sudeep,

On 15/05/2023 11:08, Sudeep Holla wrote:
> On Thu, May 11, 2023 at 10:35:37AM +0100, Ayan Kumar Halder wrote:
>> Hi Device Tree engineers,
>>
>> Recently I have ported Xen on Cortex-R52 (AArch32-V8R processor) for our AMD
>> platform.
>>
> I remember that there was some exploration on feasibility of using PSCI
> here. What happened to that ? Any summary why that was dropped ?
We are discussing internally with other Xilinx/AMD engineers about this.
>
>> I was discussing with xen-devel community about how we can properly support
>> smpboot when I was suggested that this might be the correct forum for
>> discussion.
>>
>> Please refer
>> https://lists.xenproject.org/archives/html/xen-devel/2023-05/msg00224.html
>> and the follow-ups for context.
>>
>>
>> The way smpboot works on our platform is as follows:-
>>
>> 1. core0 writes to register (say regA) the address of the secondary core
>> initialization routine.
>>
>> 2. core0 writes to another register (say regB) the value "0x1" to put the
>> secondary core in reset mode.
>>
>> 3. core0 writes to regB the value "0x0" to pull the secondary core out of
>> reset mode.
>>
>> regA, regB will differ for core1, core2, core3 and so on.
>>
> Sounds OK but will you ever need to support power management on these cores ?
> If so, just start with PSCI or provide reasons as why it doesn't fit well
> before exploring and extending the existing spin table bindings.

Power management is not in scope.

About PSCI, we are discussing internally.

>
>> Currently, I am trying to bringup core1 only.
>>
>>
>> I am thinking to use "enable-method=spin-table" in the cpu node for core1.
>> So that I can use "cpu-release-address" for regA.
>>
>> For regB, I am thinking of introducing a new property "amd-cpu-reset-addr"
>> in the cpu node.
>>
>> Please let me know your thoughts on this approach. I am also open to any
>> alternative suggestions.
>>
>>
>> Also I see that in https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/devicetree/bindings/arm/cpus.yaml#L87
>> , "arm,cortex-r52" is missing.
>>
> Yes that should be fine IMO.
>
>> Can I submit a patch (a one line change) to add this ?
>>
> Of course, it makes it easy to accept or reject rather than this question
> hidden as part of other discussion.

I have submitted a patch for this.

https://archive.armlinux.org.uk/lurker/message/20230518.152730.c91cc994.en.html

- Ayan

>
> --
> Regards,
> Sudeep