linux-kernel - Re: [PATCH 1/2] dt-bindings: mailbox: add support for referencing controllers solely by node

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Message-ID: <20241220-carving-diagram-a27c04aafb10@spud>
Date: Fri, 20 Dec 2024 19:41:57 +0000
From: Conor Dooley <conor@...nel.org>
To: Tudor Ambarus <tudor.ambarus@...aro.org>
Cc: Conor Dooley <conor.dooley@...rochip.com>,
	Jassi Brar <jassisinghbrar@...il.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, andre.draszik@...aro.org,
	peter.griffin@...aro.org, kernel-team@...roid.com,
	willmcvicker@...gle.com, daniel.lezcano@...aro.org,
	vincent.guittot@...aro.org, ulf.hansson@...aro.org, arnd@...db.de
Subject: Re: [PATCH 1/2] dt-bindings: mailbox: add support for referencing
 controllers solely by node

On Fri, Dec 20, 2024 at 07:51:32AM +0000, Tudor Ambarus wrote:
> 
> 
> On 12/19/24 6:58 PM, Conor Dooley wrote:
> > On Thu, Dec 19, 2024 at 03:42:11PM +0000, Tudor Ambarus wrote:
> >> Hi, Conor,
> >>
> >> On 12/19/24 2:11 PM, Conor Dooley wrote:
> >>>> There are mailbox clients that can discover the mailbox channel ID at
> >>>> run-time. For such cases passing the channel identifier via DT is
> >>>> redundant. Add support for referencing controllers solely by node.
> >>> I don't really get your implementation, why not just allow #mbox-cells = 0?
> >>> That's what's done for things like fixed frequency clocks that only have
> >>> a single output.
> >>
> >> Ah, indeed!
> >>
> >> instead of:
> >> 	of_parse_phandle(dev->of_node, "mbox", 0);
> >> I can do a:
> >> 	of_parse_phandle_with_args(dev->of_node, "mboxes",
> >>                                    "#mbox-cells", 0, &of_args)
> >> where #mbox-cells = 0;
> >>
> >> Or ... can I pass NULL for cells_name and make the #mbox-cells property
> >> optional and still keeping its requirement of being at least 1?
> > 
> > I think the mbox-cells = 0 approach is preferred, that property is what
> > marks it as a mailbox controller after all. Perhaps Rob or Krzysztof can
> > comment?
> 
> I think using mbox-cells = 0 is better indeed. In my proposal I
> considered the list to always have a single phandle, thus a reference to
> a single mailbox controller, whereas it may be possible that clients to
> reference multiple mailbox controllers. If so, #mbox-cells needs to be
> defined in all the controllers, for consistency reasons, similar to what
> happens with fixed clocks, as you already mentioned.

Oh right, I had totally forgotten about that, that's a solid argument
for the mbox-cells = 0 approach for sure.

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