linux-kernel - Re: [PATCH v1 2/5] dt-bindings: mailbox: add binding for Microchip IPC mailbox driver

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Message-ID: <20240919-useable-margarine-d6eefae9485c@squawk>
Date: Thu, 19 Sep 2024 08:40:09 +0100
From: Conor Dooley <conor@...nel.org>
To: Rob Herring <robh@...nel.org>
Cc: Samuel Holland <samuel.holland@...ive.com>,
	Valentina Fernandez <valentina.fernandezalanis@...rochip.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-remoteproc@...r.kernel.org,
	paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	peterlin@...estech.com, dminus@...estech.com, ycliang@...estech.com,
	jassisinghbrar@...il.com, krzk+dt@...nel.org, andersson@...nel.org,
	mathieu.poirier@...aro.org, conor+dt@...nel.org,
	conor.dooley@...rochip.com
Subject: Re: [PATCH v1 2/5] dt-bindings: mailbox: add binding for Microchip
 IPC mailbox driver

On Wed, Sep 18, 2024 at 10:35:58AM -0500, Rob Herring wrote:
> On Mon, Sep 16, 2024 at 05:31:36PM +0100, Conor Dooley wrote:
> > On Thu, Sep 12, 2024 at 04:23:44PM -0500, Samuel Holland wrote:
> > > Hi Valentina,
> > > 
> > > On 2024-09-12 12:00 PM, Valentina Fernandez wrote:
> > > > Add a dt-binding for the Microchip Inter-Processor Communication (IPC)
> > > > mailbox controller.
> > > > 
> > > > Signed-off-by: Valentina Fernandez <valentina.fernandezalanis@...rochip.com>
> > > > ---
> > > >  .../bindings/mailbox/microchip,sbi-ipc.yaml   | 115 ++++++++++++++++++
> > > >  1 file changed, 115 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/mailbox/microchip,sbi-ipc.yaml
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/mailbox/microchip,sbi-ipc.yaml b/Documentation/devicetree/bindings/mailbox/microchip,sbi-ipc.yaml
> > > > new file mode 100644
> > > > index 000000000000..dc2cbd5eb28f
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/mailbox/microchip,sbi-ipc.yaml
> > > > @@ -0,0 +1,115 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/mailbox/microchip,sbi-ipc.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Microchip Inter-processor communication (IPC) mailbox controller
> > > > +
> > > > +maintainers:
> > > > +  - Valentina Fernandez <valentina.fernandezalanis@...rochip.com>
> > > > +
> > > > +description:
> > > > +  The Microchip Inter-processor Communication (IPC) facilitates
> > > > +  message passing between processors using an interrupt signaling
> > > > +  mechanism.
> > > > +  This SBI interface is compatible with the Mi-V Inter-hart
> > > > +  Communication (IHC) IP.
> > > > +  The microchip,sbi-ipc compatible string is inteded for use by software
> > > > +  running in supervisor privileged mode (s-mode). The SoC-specific
> > > > +  compatibles are inteded for use by the SBI implementation in machine
> > > > +  mode (m-mode).
> > > 
> > > There is a lot of conditional logic in this binding for how small it is. Would
> > > it make sense to split this into two separate bindings? For example, with the
> > > current binding microchip,ihc-chan-disabled-mask is allowed for the SBI
> > > interface, but doesn't look like it belongs there.
> > 
> > I dunno. Part of me says that because this is two compatibles for the
> > same piece of hardware (the choice depending on which programming model
> > you use) they should be documented together. The other part of me is of
> > the opinion that they effectively describe different things, given one
> > describes the hardware and the other describes a firmware interface that
> > may have any sort of hardware backing it.
> > 
> > I suppose it's more of a problem for "us" (that being me/Rob/Krzysztof)
> > than for Valentina, and how to handle firmware interfaces to hardware
> > like this is one of the topics that's planned for Krzysztof's devicetree
> > BoF session at LPC.
> 
> If how the client interacts with the device is fundamentally different, 
> then I think different compatibles is fine.

It wasn't about different compatibles (which I think are non-debatable
here) it's whether or not the different compatibles should be in their
own binding files.

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