linux-kernel - Re: [PATCH] firmware: arm_scmi: Give SMC transport precedence over mailbox

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Message-ID: <ZwPeiUwT7OAgxXFl@bogus>
Date: Mon, 7 Oct 2024 14:13:45 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Florian Fainelli <florian.fainelli@...adcom.com>
Cc: linux-arm-kernel@...ts.infread.org, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Cristian Marussi <cristian.marussi@....com>,
	devicetree@...r.kernel.org (open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS),
	linux-kernel@...r.kernel.org (open list),
	arm-scmi@...r.kernel.org (open list:SYSTEM CONTROL & POWER/MANAGEMENT INTERFACE),
	linux-arm-kernel@...ts.infradead.org (moderated list:SYSTEM CONTROL & POWER/MANAGEMENT INTERFACE),
	justin.chen@...adcom.com, opendmb@...il.com,
	kapil.hali@...adcom.com, bcm-kernel-feedback-list@...adcom.com,
	Sudeep Holla <sudeep.holla@....com>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] firmware: arm_scmi: Give SMC transport precedence over
 mailbox

On Sat, Oct 05, 2024 at 09:33:17PM -0700, Florian Fainelli wrote:
> Broadcom STB platforms have for historical reasons included both
> "arm,scmi-smc" and "arm,scmi" in their SCMI Device Tree node compatible
> string.
>

I assume in the same order.

> After the commit cited in the Fixes tag and with a kernel
> configuration that enables both the SCMI and the Mailbox transports, we

^^^^^ s/SCMI/SMC ?

> would probe the mailbox transport, but fail to complete since we would
> not have a mailbox driver available.
>

I always assumed the node compatible match happens from the more specific
compatible(on the left) to the more generic ones(on the right) from the
compatible property list. Looks like that was a wrong assumption then ?

> By keeping the SMC transport objects linked first, we can let the
> platform driver, match the compatible string and probe successfully with
> no adverse effects on platforms using the mailbox transport.
>

I don't have strong objection to the patch itself, happy to get it merged.
Just curious if my understanding of the issue is correct. I think Cristian
has more detailed query, so just responding to that will suffice.

> Fixes: b53515fa177c ("firmware: arm_scmi: Make MBOX transport a standalone driver")
> Signed-off-by: Florian Fainelli <florian.fainelli@...adcom.com>
> Change-Id: I8e348e3e0deabdc5c1d596929d7f9134793f346e

Spurious from internal gerrit repo ?

--
Regards,
Sudeep