Message-ID: <026296c8-a460-43ca-a423-0fa38269fbc2@kernel.org>
Date: Mon, 10 Mar 2025 12:41:06 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Lee Jones <lee@...nel.org>,
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
 Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Lorenzo Bianconi <lorenzo@...nel.org>, Daniel Danzberger <dd@...edd.com>,
 Arnd Bergmann <arnd@...db.de>, Linus Walleij <linus.walleij@...aro.org>,
 Nikita Shubin <nikita.shubin@...uefel.me>, Guo Ren <guoren@...nel.org>,
 Yangyu Chen <cyy@...self.name>, Ben Hutchings <ben@...adent.org.uk>,
 Felix Fietkau <nbd@....name>, linux-clk@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-phy@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org, linux-usb@...r.kernel.org,
 upstream@...oha.com
Subject: Re: [PATCH 05/13] dt-bindings: mfd: add Documentation for Airoha
 EN7581 SCU

On 10/03/2025 11:47, Christian Marangi wrote:
> On Mon, Mar 10, 2025 at 10:21:45AM +0100, Krzysztof Kozlowski wrote:
>> On 09/03/2025 14:29, Christian Marangi wrote:
>>> Add Documentation for Airoha EN7581 SCU.
>>>
>>> Airoha EN7581 SoC expose registers to control miscellaneous pheriperals
>>> via the SCU (System Controller Unit).
>>>
>>> Example of these pheriperals are reset-controller, clock-controller,
>>> PCIe line speed controller and bits to configure different Serdes ports
>>> for USB or Ethernet usage.
>>>
>>> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
>>> ---
>>>  .../mfd/airoha,en7581-scu-sysctl.yaml         | 68 +++++++++++++++++++
>>>  1 file changed, 68 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/mfd/airoha,en7581-scu-sysctl.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/mfd/airoha,en7581-scu-sysctl.yaml b/Documentation/devicetree/bindings/mfd/airoha,en7581-scu-sysctl.yaml
>>> new file mode 100644
>>> index 000000000000..d7dc66f912c1
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/mfd/airoha,en7581-scu-sysctl.yaml
>>> @@ -0,0 +1,68 @@
>>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/mfd/airoha,en7581-scu-sysctl.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: Airoha EN7581 SCU (System Controller Unit)
>>> +
>>> +maintainers:
>>> +  - Christian Marangi <ansuelsmth@...il.com>
>>> +
>>> +description:
>>> +  Airoha EN7581 SoC expose registers to control miscellaneous
>>> +  pheriperals via the SCU (System Controller Unit).
>>> +
>> One more comment - there is no such thing as "sysctl" in your hardware.
>> Look at the SCU binding which clearly says that it is the hardware you
>> are duplicating here, so the "System Control Unit".
>>
>> So you have existing "This node defines the System Control Unit of the
>> EN7523 SoC" and you add one more node which defines the "System Control
>> Unit", so you have two "System Control Unit" device nodes?
>>
>> Look also what Stephen asked for:
>>
>> https://lore.kernel.org/all/20220106013100.842FCC36AEB@smtp.kernel.org/
>>
>> so how system-controller can now became clock-controller? Now, it was
>> the system controller since the beginning.
>>
> 
> The main problem here (and we had a similar problem with GPIO and PWM)
> is that the Vendor (Airoha) wasn't so bright in placing the different
> registers for the SoC so we have case where everything is mixed and not
> one after another... 
> 
> Example we have 
> - CLK register part 1
> - Some bits that configure PCIe
> - CLK register part 2
> - GPIO
> - CLK register part 3
> - ...

This does not explain that binding said "This node defines the System
Control Unit".

So what are you adding here if not SCU?

> 
> The driver solution for this is syscon and the simple-mfd node
> structure.

Let's keep driver entirely separate, we don't talk about them and mixing
arguments won't make it easier.

> 
> Now the main problem is how to modle this in DT. There are lots of case
> where the simple-mfd model is used (like the one proposed) but probably
> this is not accepted anymore. But again this should be clearly stated or
> we have a chicken-egg problem when other devs implement similar thing and
> have to implement simple MFD driver to handle this. (and driver
> maintainers say "Use the simple-mfd model like it was already done)

simple-mfd has nothing to do here. Describe the hardware - what is the SCU?


> 
> For this specific case (and to give an answer to the clock patch after
> this) the problem is that this register space was originally used only
> to control the clock and I wasn't aware that it was also used to control
> USB. Now that I'm implementing support for it, the disaster happened.
> 
> So In short SCU is lots of thing, both a system-controller, a
> clock-controller and even a reset-controller.

And you have bindings for that already. Done.

> 
> To make it short, 2 different solution:
> 1. We can keep the current node structure of the node-controller and add a
> child node for the SSR part (with a dedicated compatible).

No, you do not add child nodes just because you want some drivers.

What is SSR? How is it a device?

> 2. Those property need to be be defined in the clock-controller node?

In the SCU node. Do you have only one SCU or more?

> 
> The ideal solution is 1. Does it work for you?
> 
> Sorry for the long post and hope you understand why this mess of
> reworking the binding.
> 


Best regards,
Krzysztof

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