Re: [PATCH 05/13] dt-bindings: mfd: add Documentation for Airoha EN7581 SCU

[Christian Marangi <ansuelsmth@gmail.com>]

On Mon, Mar 10, 2025 at 12:41:06PM +0100, Krzysztof Kozlowski wrote:
> 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@gmail.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@gmail.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?
>

With "This node defines the System Control Unit" I mean, the entire
register space of the IP block is defined and each child specifically
define each part of the IP block.

> > 
> > 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.
> 

Ok.

> > 
> > 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?
> 
> 

As I said below, SCU is just the name used in Airoha Documentation for
this IP block. In this register space there are multiple things so it's
not strictly a clock-controller (as it's currently defined)

It was proposed as clock-controller previously as we weren't aware this
IP block was used also for other usage that a strict clock controller.

> > 
> > 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.
> 

It's currently defined in DTS as clock-controller, should we change it
to system-controller to make it more clear?

> > 
> > 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?

SSR is the name used in Documentation for the register used to configure
the Serdes and PCIe port.

> 
> > 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?

Strictly speaking it's one register space. One clock-controller, one
reset-controller and one set of SSR registers, and from what I can
understand it's ALWAYS "One device/compatible for Register space"

The simple-mfd pattern can't really work for case like this where in one
register space there are multiple stuff.

Is everything clear now?

To summarize:
- no child nodes
- add additional property for SSR in the SCU .yaml

> 
> > 
> > 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

-- 
	Ansuel