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Wed, 29 Oct 2025 11:47:45 -0700 (PDT) Date: Wed, 29 Oct 2025 21:47:41 +0300 From: Dan Carpenter To: Conor Dooley Cc: Lee Jones , Rob Herring , Krzysztof Kozlowski , Conor Dooley , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] dt-bindings: mfd: syscon: introduce no-auto-mmio property for syscons Message-ID: References: <230cf12861a4f0b9effc72522444d3e28c1de2c9.1761753288.git.dan.carpenter@linaro.org> <20251029-ambiance-snooper-43dc00dcee68@spud> <20251029-embroider-plunging-6356f50c7acd@spud> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251029-embroider-plunging-6356f50c7acd@spud> On Wed, Oct 29, 2025 at 06:37:26PM +0000, Conor Dooley wrote: > On Wed, Oct 29, 2025 at 08:41:51PM +0300, Dan Carpenter wrote: > > On Wed, Oct 29, 2025 at 05:33:48PM +0000, Conor Dooley wrote: > > > On Wed, Oct 29, 2025 at 08:27:05PM +0300, Dan Carpenter wrote: > > > > Generally, syscons are created automatically and accessed direclty via > > > > MMIO however sometimes syscons might only be accessible from the secure > > > > partition or through SCMI etc. Introduce the no-auto-mmio property to > > > > tell the operating system that the syscon needs to be handled manually. > > > > > > "System controller node represents a register region containing a set > > > of miscellaneous registers." > > > > > > If this isn't actually a register region, but is instead an interface > > > provided by SCMI or whatever "secure partition" is (optee?), why is the > > > syscon compatible being used for the device in the first place? > > > > In the case that I'm looking at, it really is a syscon. So right now > > we're upstreaming it and it's an MMIO syscon. Very straight forward. > > But later, I guess, they want to have a new firmware which will only let > > you access the same registers through SCMI. > > When the programming model changes, the compatible should too, no? > I wasn't planning on it. I haven't been asked to upstream the SCMI module but once my thinking was the transition would work like this. Step 1: It would work as is with an MMIO syscon. Step 2: We would upstream the SCMI driver which would provide an MMIO syscon as a fallback. At that stage you would still get an MMIO yscon regardless of whether the phandle was parsed before or after the driver loaded. Step 3: We would set the no-auto-mmio property so you have to use the driver and update the firmware so only the SCMI interface can be used. regards, dan carpenter