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

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Message-ID: <20240918153558.GA1567736-robh@kernel.org>
Date: Wed, 18 Sep 2024 10:35:58 -0500
From: Rob Herring <robh@...nel.org>
To: Conor Dooley <conor@...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 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.

Rob