linux-kernel - RE: [PATCH v2 3/3] mfd: syscon: Allow syscon nodes without a "syscon" compatible

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Message-ID: <000301db54e0$a45912b0$ed0b3810$@samsung.com>
Date: Mon, 23 Dec 2024 07:46:11 +0530
From: "Pankaj Dubey" <pankaj.dubey@...sung.com>
To: "'Rob Herring \(Arm\)'" <robh@...nel.org>, "'Lee Jones'"
	<lee@...nel.org>, "'Arnd Bergmann'" <arnd@...db.de>, "'Heiko Stuebner'"
	<heiko@...ech.de>, "'Liviu Dudau'" <liviu.dudau@....com>, "'Sudeep Holla'"
	<sudeep.holla@....com>, "'Lorenzo	Pieralisi'" <lpieralisi@...nel.org>
Cc: "'Peter Griffin'" <peter.griffin@...aro.org>, "'Will McVicker'"
	<willmcvicker@...gle.com>, "'John Madieu'" <john.madieu.xa@...renesas.com>,
	"'Krzysztof Kozlowski'" <krzysztof.kozlowski@...aro.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v2 3/3] mfd: syscon: Allow syscon nodes without a
 "syscon" compatible



> -----Original Message-----
> From: Rob Herring (Arm) <robh@...nel.org>
> Sent: Tuesday, December 17, 2024 11:42 PM
> To: Lee Jones <lee@...nel.org>; Arnd Bergmann <arnd@...db.de>; Pankaj
> Dubey <pankaj.dubey@...sung.com>; Heiko Stuebner <heiko@...ech.de>;
> Liviu Dudau <liviu.dudau@....com>; Sudeep Holla <sudeep.holla@....com>;
> Lorenzo Pieralisi <lpieralisi@...nel.org>
> Cc: Peter Griffin <peter.griffin@...aro.org>; Will McVicker
> <willmcvicker@...gle.com>; John Madieu <john.madieu.xa@...renesas.com>;
> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>; linux-
> kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org
> Subject: [PATCH v2 3/3] mfd: syscon: Allow syscon nodes without a "syscon"
> compatible
> 
> of_syscon_register_regmap() was added for nodes which need a custom regmap
> setup. It's not really correct for those nodes to claim they are compatible with
> "syscon" as the default handling likely doesn't work in those cases. If
> device_node_get_regmap() happens to be called first, then of_syscon_register()
> will be called and an incorrect regmap will be created (barring some other error).
> That may lead to unknown results in the worst case. In the best case,
> of_syscon_register_regmap() will fail with -EEXIST. This problem remains unless
> these cases drop "syscon" (an ABI issue) or we exclude them using their specific
> compatible. ATM, there is only one user: "google,gs101-pmu"
> 
> There are also cases of adding "syscon" compatible to existing nodes after the
> fact in order to register the syscon. That presents a potential DT ABI problem.
> Instead, if there's a kernel change needing a syscon for a node, then it should be
> possible to allow the kernel to register a syscon without a DT change. That's
> only possible by using
> of_syscon_register_regmap() currently, but in the future we may want to
> support a match list for cases which don't need a custom regmap.
> 
> With this change, the lookup functions will succeed for any node registered by
> of_syscon_register_regmap() regardless of whether the node compatible
> contains "syscon".
> 
> Signed-off-by: Rob Herring (Arm) <robh@...nel.org>
> ---

Reviewed-by: Pankaj Dubey <pankaj.dubey@...sung.com>

Thanks,
Pankaj Dubey