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Wed, 27 May 2026 07:35:16 -0700 (PDT) From: Wadim Mueller To: Jonathan Cameron Cc: lars@metafoo.de, dlechner@baylibre.com, nuno.sa@analog.com, andy@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, linux@roeck-us.net, jdelvare@suse.com, ak@it-klinger.de, linux-iio@vger.kernel.org, linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v1 0/4] iio: add Sensirion SLF3x liquid flow sensor support Date: Wed, 27 May 2026 16:34:58 +0200 Message-ID: <20260527143515.102794-1-wafgo01@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260526171214.750c2e25@jic23-huawei> References: <20260524205112.26638-1-wafgo01@gmail.com> <20260526171214.750c2e25@jic23-huawei> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Tue, 26 May 2026 17:12:14 +0100 Jonathan Cameron wrote: > > 1. Subsystem. Liquid-flow sensors don't seem to have a home in > > mainline yet. iio/ feels like the natural place for me, but > > please correct me if hwmon (or somewhere else) is prefered. > > I'm fine with this type of sensor in IIO, but open to hear from others! Thanks - keeping it in iio/ for v2. > > 2. Channel type. IIO has no flow channel type so far. The series > > adds IIO_VOLUMEFLOW with _scale in litres per second per LSB, > > so drivers reporting smaller units only need a fractional scale. > > IIO_MASSFLOW (for gas-flow sensors) was left out on purpose -- > > happy to add it in the same series if that's more usefull. > > Would be good to have a little more detail on difference etc to have > that discussion. Superficially I'm assuming this is a compressible vs > non compressible thing? Right - that was the distinction I had in mind: - IIO_VOLUMEFLOW: volumetric rate (m^3/s in SI, exposed as l/s), well-defined for an incompressible fluid where the volume at the sensor equals the volume delivered. This matches all "liquid flow" sensors I'm aware of (and the SLF3S family in particular). - IIO_MASSFLOW: mass rate (kg/s), the natural unit for gases because the volumetric rate depends on temperature and pressure. Most "gas flow" parts on the market (Sensirion SFM3xxx, SFC, MFC devices) actually report a "standard volume flow" (e.g. slm at 0 degC and 1013 mbar) which is just a fixed-density restatement of mass flow. I left IIO_MASSFLOW out of this series because I don't have a driver needing it right now, but if you'd prefer I add it as a stub here (name + ABI entry) so the two siblings land together, I can fold that in for v2 -- happy either way. > > 3. Subdirectory. I put the driver in a new drivers/iio/flow/ > > since there is no flow subsytem in iio yet. If colocating with > > drivers/iio/pressure/ (next to sdp500) is preferred I'll respin. > > This is easy to change later if we make a wrong decision. For now I think > iio/flow is fine. Sticking with drivers/iio/flow/ for v2. Thanks! v2 is up, addressing the inline review feedback from you and Guenter. Dropping the RFC tag since the three high-level questions are answered. Wadim