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Mon, 13 Jul 2026 08:23:58 -0700 (PDT) X-Received: by 2002:a17:903:2f08:b0:2ce:e75f:b713 with SMTP id d9443c01a7336-2cee75fbe28mr3254495ad.23.1783956237827; Mon, 13 Jul 2026 08:23:57 -0700 (PDT) Received: from localhost ([50.35.46.84]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ccc9d1edb0sm100605175ad.53.2026.07.13.08.23.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Jul 2026 08:23:57 -0700 (PDT) Date: Mon, 13 Jul 2026 08:24:00 -0700 From: Jonathan Cameron To: David Lechner Cc: Jonathan Cameron , Nuno =?ISO-8859-1?Q?S=E1?= , Andy Shevchenko , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Chris Hall , Patrick Edwards , Kurt Borja , Nguyen Minh Tien , linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 4/8] dt-bindings: iio: adc: add input-chopping property Message-ID: <20260713082400.000024f1@oss.qualcomm.com> In-Reply-To: <1700ed07-47b5-4831-87c5-a6115928baab@baylibre.com> References: <20260710-iio-adc-ti-ads122c14-v3-0-746d52cbf1d0@baylibre.com> <20260710-iio-adc-ti-ads122c14-v3-4-746d52cbf1d0@baylibre.com> <20260713023443.1a7a9acb@jic23-huawei> <1700ed07-47b5-4831-87c5-a6115928baab@baylibre.com> Organization: Qualcomm X-Mailer: Claws Mail 4.4.0 (GTK 3.24.51; x86_64-w64-mingw32) 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-Transfer-Encoding: 7bit X-Proofpoint-ORIG-GUID: UpWDzp16gDbzFxfGMsvh5dhPRTtNu0cc X-Proofpoint-Spam-Info: AW1haW4tMjYwNzEzMDE2MCBTYWx0ZWRfX2xUJuy9Tb9LI b5kg1MbriwgSMZhTEbp5HIYPrDyoBwBulkHgnNH9TJlTKdr9J1FGcPoxh2T0Bssn7Mzj1OK9Tol JBn2i70i1541Utwmz12xfop1E1pS5OU= X-Authority-Analysis: v=2.4 cv=e6c2j6p/ c=1 sm=1 tr=0 ts=6a55030f cx=c_pps a=oF/VQ+ItUULfLr/lQ2/icg==:117 a=qC1CW/w66vtJz1P9yTJxNA==:17 a=kj9zAlcOel0A:10 a=RAioF0-LDSMA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=YMgV9FUhrdKAYTUUvYB2:22 a=IpJZQVW2AAAA:8 a=ALuaPTNhsiHwyfqByDAA:9 a=CjuIK1q_8ugA:10 a=3WC7DwWrALyhR5TkjVHa:22 a=IawgGOuG5U0WyFbmm1f5:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzEzMDE2MCBTYWx0ZWRfX1QvEySd8T+4y YAmrXgy27cuOjy5Oe4d8FWreGMkmwZOIE04BX9PjycLXSrfng+RJjKRophF9AGgdlEMqfVWH6RE yKpbRvTABiMCqbuI73ccXMGb+aoYoLg0mEN+0+1gDM6qRINBAREaw/WPTukJ8HTxsDLzbQjbIGc VwNwLpfYOu6kinBv9Bc2qYF91gynbED8tFqEr80IWwPaXT+y82GCcLLxzIJoI5wd7y8W6C77/Ew Ein84pA34cLSBerXcgJ+AZlDl2yCd/KP2SqI+PQKbqjrSJAdDDzZ6ESaGGn9dsdAf+8uHOtwWln P89cW9rMxAPeFH0WTPt3zNhN6hgk9xY1mO79lM8ItkkQcpchszMTZjG3czUOVbZTTozGq3zD+Sl 5OYgR/7nzscVilGmTKFf/8Jxr2KzJUpFpKl0CIewpga5KxK+bB6SWmflmEGgjf43un1bg70k5Bc 6RWtFGV6z0p9WFU8Lsg== X-Proofpoint-GUID: UpWDzp16gDbzFxfGMsvh5dhPRTtNu0cc X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-13_04,2026-07-10_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 clxscore=1015 phishscore=0 lowpriorityscore=0 spamscore=0 adultscore=0 malwarescore=0 impostorscore=0 suspectscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607130160 On Mon, 13 Jul 2026 09:55:53 -0500 David Lechner wrote: > On 7/12/26 8:34 PM, Jonathan Cameron wrote: > > On Fri, 10 Jul 2026 17:50:37 -0500 > > "David Lechner (TI)" wrote: > > > >> Add a generic input-chopping property to adc.yaml. This is a feature > >> seen frequently in ADCs that are designed to measure resistive loads, > >> such as RTDs and strain gauges. Enabling this can reduce offset errors > >> by swapping the positive and negative input channels on every other > >> conversion. This can have side-effects in timing and filter response, so > >> it is not always desirable to enable this feature in some applications. > >> Therefore, it is best to make this a property that can be enabled or > >> disabled in the device tree. > >> > >> Signed-off-by: David Lechner (TI) > >> --- > >> v3 changes: > >> * Renamed property to input-chopping to reflect more common terminology. > >> * Removed "allowed" from the description. > >> * Extended description to explain when it should not be used. > >> > >> v2 changes: > >> * New patch. > >> --- > >> Documentation/devicetree/bindings/iio/adc/adc.yaml | 8 ++++++++ > >> 1 file changed, 8 insertions(+) > >> > >> diff --git a/Documentation/devicetree/bindings/iio/adc/adc.yaml b/Documentation/devicetree/bindings/iio/adc/adc.yaml > >> index 308857f11220..c408feebd46d 100644 > >> --- a/Documentation/devicetree/bindings/iio/adc/adc.yaml > >> +++ b/Documentation/devicetree/bindings/iio/adc/adc.yaml > >> @@ -80,6 +80,14 @@ properties: > >> ADCs usually allow choosing between internal reference sources or a pair > >> of external pins. > >> > >> + input-chopping: > >> + type: boolean > >> + description: > >> + If set, the positive and negative input channels are swapped on every > >> + other conversion to reduce offset error. This generally comes at the > >> + expense of added settling time between conversions, so should be omitted > >> + on systems with high-frequency signals or high data rate requirements. > > > > I'm lazy so I didn't check back, but in my mental model of this, the DT is simply > > saying that the analog circuitry is suitable for doing chopping. Driver decision > > on whether to do it. Perhaps we can reword it for that? > > Heh, that was the "allowed" part that I removed. > > I think this is really more of a design decision between the tradeoff > of less noise vs. data rate. By setting this property, we are saying > we should favor less noise. So I think it is more about the expected > signal than the circuitry. > > So not sure that I would add anything here. Fair enough. Given the driver can always ignore what is in DT I guess it is fine as is. Thanks, Jonathan > > > >> + > >> excitation-channels: > >> $ref: /schemas/types.yaml#/definitions/uint32-array > >> description: > >> > > > >