[PATCH v2 1/3] dt-bindings: nvmem: syscon: Add syscon backed nvmem bindings

[Marek Vasut]

On 5/31/23 21:37, Krzysztof Kozlowski wrote:
> On 24/05/2023 05:30, Marek Vasut wrote:
>> On 5/18/23 16:26, Krzysztof Kozlowski wrote:
>>> On 17/05/2023 17:25, Marek Vasut wrote:
>>>> Add trivial bindings for driver which permits exposing syscon backed
>>>> register to userspace. This is useful e.g. to expose U-Boot boot
>>>> counter on various platforms where the boot counter is stored in
>>>> random volatile register, like STM32MP15xx TAMP_BKPxR register.
>>>>
>>>> Signed-off-by: Marek Vasut <marex at denx.de>
>>>> ---
>>>> Cc: Alexandre Torgue <alexandre.torgue at foss.st.com>
>>>> Cc: Conor Dooley <conor+dt at kernel.org>
>>>> Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt at linaro.org>
>>>> Cc: Marek Vasut <marex at denx.de>
>>>> Cc: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
>>>> Cc: Rob Herring <robh+dt at kernel.org>
>>>> Cc: Srinivas Kandagatla <srinivas.kandagatla at linaro.org>
>>>> Cc: devicetree at vger.kernel.org
>>>> Cc: kernel at dh-electronics.com
>>>> Cc: linux-arm-kernel at lists.infradead.org
>>>> Cc: linux-stm32 at st-md-mailman.stormreply.com
>>>> ---
>>>> V2: Use generic syscon supernode
>>>> ---
>>>>    .../bindings/nvmem/nvmem-syscon.yaml          | 39 +++++++++++++++++++
>>>>    1 file changed, 39 insertions(+)
>>>>    create mode 100644 Documentation/devicetree/bindings/nvmem/nvmem-syscon.yaml
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/nvmem/nvmem-syscon.yaml b/Documentation/devicetree/bindings/nvmem/nvmem-syscon.yaml
>>>> new file mode 100644
>>>> index 0000000000000..7c1173a1a6218
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/nvmem/nvmem-syscon.yaml
>>>> @@ -0,0 +1,39 @@
>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>> +%YAML 1.2
>>>> +---
>>>> +$id: http://devicetree.org/schemas/nvmem/nvmem-syscon.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: Generic syscon backed nvmem
>>>> +
>>>> +maintainers:
>>>> +  - Marek Vasut <marex at denx.de>
>>>> +
>>>> +allOf:
>>>> +  - $ref: "nvmem.yaml#"
>>>
>>> Usual comment: drop quotes. We removed them everywhere, so you based
>>> your work on some old tree.
>>>
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    enum:
>>>> +      - nvmem-syscon
>>>> +
>>>> +  reg:
>>>> +    maxItems: 1
>>>
>>> Rob's questions are not solved.
>>
>> Can you reiterate this one ? I likely missed it.
> 
> You did not solve the case of more than one register. This isn't an odd
> case.

So why not just extend the bindings to support

reg = <0x14c 0x4>, <0x180 0x10>, ... ;

this kind of stuff ?

>>> The nvmem.yaml schema expects here to
>>> allow children. This should not be created per-register, but per entire
>>> block of registers.
>>
>> This thing works the other way around, I have a syscon register block
>> already, and I want to expose subset of it to userspace as read/write
>> accessible file to expose bootcounter available in that register (so I
>> can read it and reset it from user application).
> 
> And this makes it too limited. I would expect one device exposing
> multiple blocks or registers, just like all nvmem providers are doing.

What would be the real-world use case of that ?