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Thu, 30 Oct 2025 01:49:51 -0700 (PDT) Date: Thu, 30 Oct 2025 11:49:47 +0300 From: Dan Carpenter To: Arnd Bergmann Cc: Lee Jones , Conor Dooley , devicetree@vger.kernel.org, Krzysztof Kozlowski , linux-kernel@vger.kernel.org, Rob Herring , =?iso-8859-1?Q?Andr=E9?= Draszik , Peter Griffin Subject: Re: [PATCH 0/2] mfd: syscon: introduce no-auto-mmio DT property Message-ID: References: <3fd4beba-0d0b-4a20-b6ed-4e00df109b66@app.fastmail.com> 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: On Thu, Oct 30, 2025 at 09:33:39AM +0100, Arnd Bergmann wrote: > On Thu, Oct 30, 2025, at 08:33, Dan Carpenter wrote: > > On Wed, Oct 29, 2025 at 08:43:33PM +0100, Arnd Bergmann wrote: > >> On Wed, Oct 29, 2025, at 18:27, Dan Carpenter wrote: > >> > Most syscons are accessed via MMMIO and created automatically. But one > >> > example of a syscon that isn't is in drivers/soc/samsung/exynos-pmu.c > >> > where the syscon can only be accessed via the secure partition. We are > >> > looking at upstreaming a different driver where the syscon will be > >> > accessed via SCMI. > >> > > >> > Normally, syscons are accessed by doing something like > >> > syscon_regmap_lookup_by_phandle_args() but that function will > >> > automatically create an MMIO syscon if one hasn't been registered. So > >> > the ordering becomes a problem. The exynos-pmu.c driver solves this > >> > but it's a bit awkward and it would be even trickier if there were > >> > several drivers accessing the same syscon. > >> > >> What would happen on the current exynos platform if we just take away > >> the 'regs' property? I would hope that we can avoid encoding what > >> is essentially operating system policy in that driver and instead > >> just describe it as a device that expects to be implemented by > >> firmware and doesn't need registers? > > > > Exynos solves this because they only have one phandle so when they parse > > it, that's when then they create the syscon. If you had multiple drivers > > accessing the same syscon then that doesn't work. > > I'm not following the logic here. Do you mean that they avoid the > issue today by ensuring that the regmap is always probed before > its only user, or do you mean something else? Yes. That's what I mean. regards, dan carpenter