Re: [PATCH v14 4/5] hw/riscv: virt: Add PMU DT node to the device tree

[<Conor.Dooley@microchip.com>]

On 28/11/2022 20:41, Atish Kumar Patra wrote:
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> On Mon, Nov 28, 2022 at 12:38 PM <Conor.Dooley@microchip.com> wrote:
>>
>> On 28/11/2022 20:16, Atish Kumar Patra wrote:
>>> On Thu, Nov 24, 2022 at 5:17 AM Conor Dooley <conor.dooley@microchip.com> wrote:
>>>>
>>>> On Wed, Aug 24, 2022 at 03:17:00PM -0700, Atish Patra wrote:
>>>>> Qemu virt machine can support few cache events and cycle/instret counters.
>>>>> It also supports counter overflow for these events.
>>>>>
>>>>> Add a DT node so that OpenSBI/Linux kernel is aware of the virt machine
>>>>> capabilities. There are some dummy nodes added for testing as well.
>>>>
>>>> Hey Atish!
>>>>
>>>> I was fiddling with dumping the virt machine dtb again today to check
>>>> some dt-binding changes I was making for the isa string would play
>>>> nicely with the virt machine & I noticed that this patch has introduced
>>>> a new validation failure:
>>>>
>>>> ./build/qemu-system-riscv64 -nographic -machine virt,dumpdtb=qemu.dtb
>>>>
>>>> dt-validate -p ../linux/Documentation/devicetree/bindings/processed-schema.json qemu.dtb
>>>> /home/conor/stuff/qemu/qemu.dtb: soc: pmu: {'riscv,event-to-mhpmcounters': [[1, 1, 524281, 2, 2, 524284, 65561, 65561, 524280, 65563, 65563, 524280, 65569, 65569, 524280, 0, 0, 0, 0, 0]], 'compatible': ['riscv,pmu']} should not be valid under {'type': 'object'}
>>>>         From schema: /home/conor/.local/lib/python3.10/site-packages/dtschema/schemas/simple-bus.yaml
>>>>
>>>> I assume this is the aforementioned "dummy" node & you have no intention
>>>> of creating a binding for this?
>>>>
>>>
>>> It is a dummy node from Linux kernel perspective. OpenSbi use this
>>> node to figure out the hpmcounter mappings.
>>
>> Aye, but should it not have a binding anyway, since they're not
>> meant to be linux specific?
>>
> It is documented in OpenSBI.
> https://github.com/riscv-software-src/opensbi/blob/master/docs/pmu_support.md
> 
> Are you suggesting that any non-Linux specific DT nodes should be part
> of Linux DT binding as well ?

I thought the point was that they were *not* meant to be linux specific,
just happening to be housed there.