Re: [PATCH 4/4] ARM: dts: uniphier: change support card to simple-mfd from simple-bus

On Mon, 29 Jun 2020, Lee Jones wrote:

On Mon, 29 Jun 2020, Masahiro Yamada wrote:

quoted

On Thu, Jun 25, 2020 at 11:57 PM Lee Jones [off-list ref] wrote:

quoted

On Thu, 25 Jun 2020, Masahiro Yamada wrote:

quoted

On Thu, Jun 25, 2020 at 3:16 AM Lee Jones [off-list ref] wrote:

quoted

On Thu, 25 Jun 2020, Masahiro Yamada wrote:

quoted

On Tue, Jun 23, 2020 at 9:24 PM Lee Jones [off-list ref] wrote:

quoted

On Tue, 23 Jun 2020, Masahiro Yamada wrote:

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'make ARCH=arm dtbs_check' emits the following warning:

  support-card@1,1f00000: $nodename:0: 'support-card@1,1f00000' does not match '^(bus|soc|axi|ahb|apb)(@[0-9a-f]+)?$'

Maybe, simple-mfd could be a better fit for this device.

The two should be equivalent.

Yes, I know.
That's why I can change "simple-bus" to "simple-mfd"
with no risk.

The difference is schema-check.

The node name for "simple-bus" is checked by 'make dtbs_check'.

See this code:
https://github.com/robherring/dt-schema/blob/v2020.05/schemas/simple-bus.yaml#L17

Even if I rename the node, it does not accept the
unit name '1,1f00000'

quoted

What do you mean by "maybe"?  Does this squash the warning?

"maybe" means I am not quite sure
which compatible is a better fit
to describe this device.

As mentioned above, simple-bus and simple-mfd
are interchangeable from a driver point of view.

This add-on board is integrated with various peripherals
such as 16550a serial, smsc9115 ether etc.
The address-decode is implemented in a CPLD device.
It has chip selects and local addresses, which are mapped to
the parent.

It can be either simple-bus or simple-mfd, I think.


dt-schema checks the node name of simple-bus.
Currently, there is no check for simple-mfd.

So, I think this patch is an easy solution
to fix the warning.

Yes, looking at the documentation it seems as though 'simple-mfd'
would be a better fit.  Is the device a single IP with various
different functions?

Not an IP.

This is a small board that consists of
a CPLD + ethernet controller + serial controller + LED, etc.

Then simple MFD does not seem like a good fit.

Neither does 'simple-bus'.

Then, I do not know what to do.


This board connection is so simple
that no hardware initialization needed to get access
to peripherals.

So, 'simple-bus' or 'simple-mfd' is preferred.

If this is not either simple-bus or simple-mfd,
I need a special driver to probe the
child devices such as ethernet, serial etc.

quoted

What is it you're trying to describe in the device hierarchy?

The connection is as follows:


|-Main board -|      |----- add-on board ----|
|             |      |     (this board)      |
|             |      |                       |
|    (SoC) ---|------|--- CPLD --- ethernet  |
|             |      |          |- serial    |
|-------------|      |          |- LED       |
                     |                       |
                     |-----------------------|



uniphier-support-card.dtsi describes the
"add-on board" part.
Address-decode is implemented in CPLD.


So, the criteria to become MFD is
whether it is an IP integrated into SoC.


- implemented in an SoC  --> MFD

If

 s/in an SoC/in a single piece of silicon/

... then yes.

quoted

- implemented in a board + CPLD  --> not MFD

Right?

Right.  Unless all H/W is represented inside the CPLD, in which case
the CPLD is, in theory, the MFD.  Although, due to the nature of
CPLDs, this is a slippery slope.

You may want something like:

  arch/arm64/boot/dts/rockchip/rk3399-roc-pc-mezzanine.dts

... where the add-on board is represented separately (not in the
same hierarchical structure as the main board.  The main board is then
included as a DTSI from the add-on board.

It might also be worth looking at how consumer boards such as the
RaspberryPi, BeagleBoard and the like handle their add-on boards,
mezzanines, capes, hats, etc.

Another option; if the add-on board PCB really doesn't do anything
except provide some copper lines to the on-board components, then does
it need representing in Device Tree at all?  I suggest not.

Your issue will come when you want to swap out that board and insert
another, which contains different functionality.  This is why it would
be better to represent the whole board as an orthogonal *.dts file.
Whether you decide to lay it out as it's own board (as above) or as
children to the system-bus will be up to you.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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