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([2600:8803:e7e4:1d00:f7b4:dfbd:5110:c59d]) by smtp.gmail.com with ESMTPSA id 5614622812f47-437ffedd355sm21206b6e.12.2025.08.30.11.48.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 30 Aug 2025 11:48:04 -0700 (PDT) Message-ID: <97f20435-e4b9-49c5-ab02-b67a8112f0ee@baylibre.com> Date: Sat, 30 Aug 2025 13:48:03 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 01/15] iio: adc: ad4030: Fix _scale for when oversampling is enabled To: Jonathan Cameron , Marcelo Schmitt Cc: linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, devicetree@vger.kernel.org, linux-spi@vger.kernel.org, Michael.Hennerich@analog.com, nuno.sa@analog.com, eblanc@baylibre.com, andy@kernel.org, corbet@lwn.net, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, broonie@kernel.org, Jonathan.Cameron@huawei.com, andriy.shevchenko@linux.intel.com, ahaslam@baylibre.com, marcelo.schmitt1@gmail.com References: <20250830194308.32def0e5@jic23-huawei> Content-Language: en-US From: David Lechner In-Reply-To: <20250830194308.32def0e5@jic23-huawei> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/30/25 1:43 PM, Jonathan Cameron wrote: > On Fri, 29 Aug 2025 21:40:24 -0300 > Marcelo Schmitt wrote: > >> Previously, the AD4030 driver was using the number of scan realbits for the >> voltage channel to derive the scale to millivolts. Though, when sample >> averaging is enabled (oversampling_ratio > 1), the number of scan realbits >> for the channel is set to 30 and doesn't match the amount of conversion >> precision bits. Due to that, the calculated channel scale did not correctly >> scale raw sample data to millivolt units in those cases. Use chip specific >> precision bits to derive the correct channel _scale on every and all >> channel configuration. >> >> Fixes: dc78e71d7c15 ("iio: adc: ad4030: remove some duplicate code") >> Signed-off-by: Marcelo Schmitt > > Hi Marcelo > > I was assuming that when this said 'averaging' it actually meant > summing (there is a note about using the upper precision bits to get the same > scaling which is what we'd expect it were simply summing over X samples). > > So given that we don't divide back down to get the original scaling I'm > not following how this works. I had the same feeling. I have some hardware I can test later this week.