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

[<Conor.Dooley@microchip.com>]

On 29/11/2022 07:08, Andrew Jones wrote:
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> On Mon, Nov 28, 2022 at 09:10:03PM +0000, Conor.Dooley@microchip.com wrote:
>> 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.
>>
> 
> I'm not sure if there's an official policy on where DT nodes should be
> specified, but it looks like Samuel's opinion is that they should live
> in the Linux kernel, whether they're used there or not [1].
> 
> [1] http://lists.infradead.org/pipermail/opensbi/2022-October/003522.html

Yah, that was also my understanding. See also U-Boot moving to unify
their custom bindings into the linux repo:
https://lore.kernel.org/linux-devicetree/20220930001410.2802843-1-sjg@chromium.org/