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Sat, 26 Dec 2020 01:45:33 +0000 From: Chris Lesiak To: Linus Walleij CC: Jean Delvare , Guenter Roeck , "linux-hwmon@vger.kernel.org" , Peter Rosin , Jonathan Cameron , "linux-iio@vger.kernel.org" Subject: Re: [PATCH v2] hwmon: (ntc_thermistor): try reading processed Thread-Topic: [PATCH v2] hwmon: (ntc_thermistor): try reading processed Thread-Index: AQHW2ZJfsXXsNRhKIU23+9Zg5xYZMaoFcfppgAL82ACAACuFAQ== Date: Sat, 26 Dec 2020 01:45:33 +0000 Message-ID: References: <20201224011607.1059534-1-linus.walleij@linaro.org> , In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: linaro.org; dkim=none (message not signed) header.d=none;linaro.org; dmarc=none action=none header.from=licor.com; x-originating-ip: [2603:80a0:801:c200:7551:df18:fd64:c52e] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 853f15a3-0bb8-4e2f-9e53-08d8a93fef71 x-ms-traffictypediagnostic: SN4PR0801MB3805: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; 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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: licor.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SN6PR08MB5565.namprd08.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 853f15a3-0bb8-4e2f-9e53-08d8a93fef71 X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Dec 2020 01:45:33.7020 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 48c70abd-da5a-4c6c-86cb-5e003ca01574 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: ix/TbzlOJe9vd/JohHuY4ETb+mh9X2UBe8cALKxlRTjATLvcnBzrVMNAR10L975vwwXLXPipkP2SBVm5huGNJg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN4PR0801MB3805 Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org Linus Walleij wrote:=0A= > I have to do this change because my ADC driver only provides processed=0A= > channels (drivers/iio/adc/ab8500-gpadc.c). It provides raw values and=0A= > it provides processed values but no scale. That means your code will=0A= > not work, sadly. It will result in the raw value being used without scali= ng.=0A= =0A= > The reason that the ADC cannot provide scaling is that the scale is not= =0A= > linear and based on calibration. IIO scaling is only linear.=0A= =0A= I haven't been able to find detailed documentation on the ab8500-gpadc,=0A= so I have a couple of questions / comments:=0A= =0A= 1. The driver appears to support temperature output directly. Why do=0A= you need ntc_thermistor?=0A= =0A= 2. I don't understand how the ab8500_gpadc_read_raw output of processed=0A= data could possibly be correct.=0A= =0A= if (mask =3D=3D IIO_CHAN_INFO_PROCESSED) {=0A= processed =3D ab8500_gpadc_ad_to_voltage(gpadc, ch->id, raw= _val);=0A= if (processed < 0)=0A= return processed;=0A= =0A= /* Return millivolt or milliamps or millicentigrades */=0A= *val =3D processed * 1000;=0A= return IIO_VAL_INT;=0A= }=0A= =0A= Note that both processed and *val are both of type int.=0A= =0A= If *val really does end up with milliVolt units, then processed must=0A= have had Volt units. And you only have single Volt resolution.=0A= =0A= Either you are working with a lot higher voltages than I usually see,=0A= or something must be wrong.=