linux-kernel - Re: [PATCH v4 1/9] dt-bindings: mfd: Add TI-Nspire misc registers

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Date:   Wed, 2 Nov 2022 16:26:45 -0500
From:   Rob Herring <robh@...nel.org>
To:     Andrew Davis <afd@...com>
Cc:     Lee Jones <lee@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Daniel Tang <dt.tangr@...il.com>,
        Fabian Vogt <fabian@...ter-vogt.de>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/9] dt-bindings: mfd: Add TI-Nspire misc registers

On Wed, Nov 02, 2022 at 02:05:28PM -0500, Andrew Davis wrote:
> On 11/2/22 12:35 PM, Rob Herring wrote:
> > On Tue, Nov 01, 2022 at 04:57:56PM -0500, Andrew Davis wrote:
> > > The TI Nspire devices contain a set of registers with a seemingly
> > > miscellaneous set of functionality. This area is known simply as the
> > > "misc" region.
> > > 
> > > Signed-off-by: Andrew Davis <afd@...com>
> > > ---
> > >   .../bindings/mfd/ti,nspire-misc.yaml          | 55 +++++++++++++++++++
> > >   1 file changed, 55 insertions(+)
> > >   create mode 100644 Documentation/devicetree/bindings/mfd/ti,nspire-misc.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/mfd/ti,nspire-misc.yaml b/Documentation/devicetree/bindings/mfd/ti,nspire-misc.yaml
> > > new file mode 100644
> > > index 0000000000000..d409eae7537bd
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/mfd/ti,nspire-misc.yaml
> > > @@ -0,0 +1,55 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > +# Copyright (C) 2022 Texas Instruments Incorporated - https://www.ti.com/
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/mfd/ti,nspire-misc.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: TI Nspire MISC hardware block
> > > +
> > > +maintainers:
> > > +  - Andrew Davis <afd@...com>
> > > +
> > > +description: |
> > > +  System controller node represents a register region containing a set
> > > +  of miscellaneous registers. The registers are not cohesive enough to
> > > +  represent as any specific type of device. The typical use-case is
> > > +  for some other node's driver, or platform-specific code, to acquire
> > > +  a reference to the syscon node (e.g. by phandle, node path, or
> > > +  search using a specific compatible value), interrogate the node (or
> > > +  associated OS driver) to determine the location of the registers,
> > > +  and access the registers directly.
> > 
> > Looks like you copied the generic description? Describe what MISC
> > contains.
> > 
> 
> I don't know what all MISC contains (or maybe I do, but it is not
> publicly available so I'm not going to add anything that hasn't
> already been found by clean-room reverse engineering [0]).

Put whatever you are comfortable with, but not a duplicate generic 
description. You know it at least it has reboot registers...

> This is the point I was trying to make in that thread on v3. The
> node's content *is* the hardware description. Every time a new
> register is found it could have just been added to the DT. But now
> we also have to go back here and add the exact same information
> to the binding, every time. We don't require that for simple-bus,
> should simple-mfd be given the same flexibility?

The thing with any MFD is it makes up a device even if it's 'simple', so 
it's important to get a full picture of the device. It could evolve to 
not being 'simple'.

For example, if you came along and wanted to make it a clock provider, 
you'd probably create a clock child node that's just a compatible and 
'#clock-cells'. The feedback would be just add '#clock-cells' to the 
'ti,nspire-misc' node. So yes, I want to see additions.

Rob