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([2600:8803:e7e4:1d00:a178:aa1c:68f0:444a]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-74647c1c2f9sm966799a34.1.2025.09.04.12.53.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Sep 2025 12:53:39 -0700 (PDT) Message-ID: <1ae7994c-4943-4a91-aea0-218c5bd331b2@baylibre.com> Date: Thu, 4 Sep 2025 14:53:38 -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 v2] iio: adc: ad7124: fix sample rate for multi-channel use To: Michael Hennerich , Jonathan Cameron , =?UTF-8?Q?Nuno_S=C3=A1?= , Andy Shevchenko Cc: linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250904-iio-adc-ad7124-fix-samp-freq-for-multi-channel-v2-1-bbf2f0d997ea@baylibre.com> From: David Lechner Content-Language: en-US In-Reply-To: <20250904-iio-adc-ad7124-fix-samp-freq-for-multi-channel-v2-1-bbf2f0d997ea@baylibre.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/4/25 11:19 AM, David Lechner wrote: > Change how the FS[10:0] field of the FILTER register is calculated to > get consistent sample rates when only one channel is enabled vs when > multiple channels are enabled in a buffered read. > > By default, the AD7124 allows larger sampling frequencies when only one > channel is enabled. It assumes that you will discard the first sample or > so to allow for settling time and then no additional settling time is > needed between samples because there is no multiplexing due to only one > channel being enabled. The conversion formula to convert between the > sampling frequency and the FS[10:0] field is: > > fADC = fCLK / (FS[10:0] x 32) > > which is what the driver has been using. > > On the other hand, when multiple channels are enabled, there is > additional settling time needed when switching between channels so the > calculation to convert between becomes: > > fADC = fCLK / (FS[10:0] x 32 x (4 + AVG - 1)) > Additional testing on top of this patch while implementing filter types has shown that this formula is actually not what we will need in the future. Rather, we will need a whole series of undocumented formulas that depends on the filter type. I will send a v3 that drops all of the AVG stuff.