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Tue, 19 Aug 2025 11:00:44 -0700 (PDT) Received: from localhost ([2804:30c:2767:3c00:70b9:40f2:fa7f:19cd]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-245ed4e9bd2sm3117445ad.106.2025.08.19.11.00.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Aug 2025 11:00:43 -0700 (PDT) Date: Tue, 19 Aug 2025 15:01:04 -0300 From: Marcelo Schmitt To: Krzysztof Kozlowski Cc: 20250816141220.0dd8d68f@jic23-huawei.smtp.subspace.kernel.org, Jonathan Cameron , Jonathan Santos , linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Michael.Hennerich@analog.com, dlechner@baylibre.com, nuno.sa@analog.com, andy@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org Subject: Re: [PATCH 1/4] dt-bindings: iio: adc: ad7768-1: add new supported parts Message-ID: References: <8c27b00c-5b80-400f-8538-b9ad96fd5feb@kernel.org> <20250816141220.0dd8d68f@jic23-huawei> <41ad5dc8-0179-49b7-a660-2c55b5048db6@kernel.org> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <41ad5dc8-0179-49b7-a660-2c55b5048db6@kernel.org> Hi, On 08/19, Krzysztof Kozlowski wrote: > On 18/08/2025 23:04, Jonathan Santos wrote: > > On 08/16, Jonathan Cameron wrote: > >> On Thu, 14 Aug 2025 08:03:23 +0200 > >> Krzysztof Kozlowski wrote: > >> > >>> On 14/08/2025 00:39, Jonathan Santos wrote: > >>>>>> > >>>>>> + adi,aaf-gain: > >>>>>> + description: | > >>>>>> + Specifies the gain of the Analog Anti-Aliasing Filter (AAF) applied to the > >>>>>> + ADC input, measured in milli-units. The AAF provides additional signal > >>>>> > >>>>> What is milli unit? Isn't gain in dB, so maybe you want mB? Quite > >>>>> unpopular to see mB, but we cannot use 1/100 of dB, so I could > >>>>> understand it. > >>>>> > >>>> > >>>> Actually, the gain is expressed in V/V, not in dB. I may have phrased it poorly, but since > >>>> there are fractional values like 0.364 and 0.143, I chose to represent it > >>>> in milli-units. > >>> > >>> Why your reply to is corrupted: > >>> "c3cf9b97-3883-4ebb-a2ed-0033adebda87@kernel.org"? > >>> > >>> > >>> What sort of unit is milli-unit? Isn't this 1/1000 of some BASE unit, > >>> but you do not have here a base? > >>> > >>> I think you want just basis point if this is V/V (already in common > >>> property suffixes) > >> Nice. I didn't know about -bp. That does sound like a good choice for ratio > >> stuff and here would be 100x larger actual values which is fine. > >> > > > > Yes, it would be, but the here it is 1000x larger than the > > actual value (1/1000 V/V). I don't see another unit in > > Huh? How? 1000x larger would be = 1... This makes no sense... > > > > property-units.yaml for this specifc case. Maybe using -milli suffix > > like in 'adi,ad4000.yaml' and 'adi,ad7380.yaml'? > After having a look at the data sheets for these parts (AD7768-1, ADAQ7767-1, ADAQ7768-1, ADAQ7769-1), I think this indeed has similar semantics to adi,gain-milli. The data sheet says the AAF selection has an impact on the -3dB cutoff frequency but, for a given ODR, there is no difference between the reported −3 dB Bandwidth (kHz) in Table 12, Table 32, and Table 35 from AD7768-1, ADAQ7767-1, and ADAQ7769-1, respectively. So, looks like this is just about signal amplification/attenuation and so the use of adi,gain-milli sounds appropriate to me. Considering the AAF doesn't really impact the -3dB cutoff frequency, maybe the property could be documented like: adi,gain-milli: description: | Specifies the gain applied by the Analog Anti-Aliasing Filter (AAF) to the ADC input (in milli units). The hardware gain is determined by which input pin(s) the signal goes through into the AAF. The possible connections are: * For the ADAQ7767-1: input signal connected to IN1±, IN2± or IN3±. * For the ADAQ7769-1: OUT_PGA pin connected to IN1_AAF+, IN2_AAF+, or IN3_AAF+. If not present, default to 1000 (no actual gain applied). $ref: /schemas/types.yaml#/definitions/uint16 enum: [143, 364, 1000] default: 1000 Would something along those lines make sense for these devices? Best regards, Marcelo