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Thu, 24 Dec 2020 03:15:55 +0000 From: Chris Lesiak To: Linus Walleij , Jean Delvare , Guenter Roeck CC: "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+9Zg5xYZMaoFcfppgAAdK/Q= Date: Thu, 24 Dec 2020 03:15:55 +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: 31cd2a92-9baf-4043-053a-08d8a7ba3a4c x-ms-traffictypediagnostic: SN6PR08MB5342: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; 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x-ms-exchange-antispam-messagedata: =?iso-8859-1?Q?Tov1sIlDI1oV8gjD1ZQP2V9OyfgMMPXDA8wZb5JWzyuTPxEbWuKWMmGvza?= =?iso-8859-1?Q?dgCTA4d4TA5uDt8vED8OW2dtAefXCBZlwdWK8dfJOPyTcpLvB/Ep+MAYWJ?= =?iso-8859-1?Q?7YmrDyl5/r5se8WSfRHJd2a136RerTWNyO8MLMLoOnXEfPKLYQhNkixVQW?= =?iso-8859-1?Q?TydPVpfkDaMMPGV447NDtK7/hzmoeialTosVLAJODNkU5y4E+W3YLUd2Bp?= =?iso-8859-1?Q?6Fm0zkRm1WglXeLCw05rfgwVvUTqwmZQ2xhbHiBh7KaYuRNawORsXSHnuF?= =?iso-8859-1?Q?A9+SUk1XcV+T+pemJEZoSRNLghY3tO4v67fGq9QQE8UM45+8AOkniQ0e7g?= =?iso-8859-1?Q?84g1Hwpy1z3LOzl0JgwQFBjVqLxkzvExmIksMPowN5AJEUntmutEKSdEYl?= =?iso-8859-1?Q?WsY5yA/Vo+Cc4QpmzP6nmBgxZexRNKDqEgJw58HY7zc+/AvT0/k5rLYTvg?= =?iso-8859-1?Q?EJq+/+J5as5gI6l/t5EZSV1svm/YdnHiFTMvorL0HUg13GPF4wglfmm0ft?= =?iso-8859-1?Q?Aux57yIpTAU/fXqKKhFCbmTTR4VhvTuTTLNM8WXlxD/c9r21MkRrbwO+6O?= =?iso-8859-1?Q?dusDaLup0foBsmM5ocyfG2dJvmFignyAjQRVUCYh5g6YEgy/xPHEXOcyXH?= =?iso-8859-1?Q?MpnTHtWYu2FnQtYXAyaxhAcjHVI+jeWLSN9YBrddnGMIYDbm6ddGPGx4dT?= =?iso-8859-1?Q?y37JZW0MYa+ZAU2JFcqzc2cW4sG4PqykWxdzFtcg4zWEqGr4cw3HgJXoMj?= =?iso-8859-1?Q?q5ZfIEMerj7FFR5C0yDPtaoythCWuW7AzM0xCOCmVsxMedxdT4PenyJIpg?= =?iso-8859-1?Q?1yPgcLN3GNJAH/DUO6DxBohIVdpbga60VTopxJWWV6RVscr+AVclIC7wtU?= =?iso-8859-1?Q?AUFCWYGf9OSTQqwcNaVA3aOUEwNAsjM1ZnqaVgLj1dM3O1dfSnG9VtnlbZ?= =?iso-8859-1?Q?aZkk+gJLmlMvV2JFrBzi4Iah2cYf1F18jKQnHvBLBtkFfH0Fioc6X/nZXo?= =?iso-8859-1?Q?ZxK6lYbD96m6liYds149hm4fhIzr5P6N/zMwfxoazV/mKwv7ZHIs0xScbY?= =?iso-8859-1?Q?jPxGP+Rq8Kj/dSR9vR6IiEU=3D?= x-ms-exchange-transport-forked: True Content-Type: text/plain; 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: 31cd2a92-9baf-4043-053a-08d8a7ba3a4c X-MS-Exchange-CrossTenant-originalarrivaltime: 24 Dec 2020 03:15:55.5781 (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: R1/I7L0ucgXl/fR/D0nIHo1APc+olxdikH26MVT5J75WjBteSMrXdxzDvVOMYw5nAVnv4CShIc3qg42qWNeHKA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR08MB5342 Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org A closer reading of the "iio: inkern: pass through raw values if no scaling= "=0A= commit leads me to believe that even when the sensor provides no scale,=0A= the returned value is expected to be in the correct units.=0A= =0A= If that is true, there was a bug in the commit.=0A= It failed to apply the caller supplied scale that ntc_thermistor.c relies o= n=0A= to convert from milliVolts to microVolts.=0A= =0A= Linus, would this change address your original problem?=0A= =0A= diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c=0A= index fe30bcb6a57b..79787474d511 100644=0A= --- a/drivers/iio/inkern.c=0A= +++ b/drivers/iio/inkern.c=0A= @@ -587,7 +587,7 @@ static int iio_convert_raw_to_processed_unlocked(struct= iio_channel *chan,=0A= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* Just pass raw values as processed if n= o scaling is=0A= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* available.=0A= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0*/=0A= - =A0 =A0 =A0 =A0 =A0 =A0 =A0 *processed =3D raw;=0A= + =A0 =A0 =A0 =A0 =A0 =A0 =A0 *processed =3D raw * scale;=0A= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 return 0;=0A= =A0 =A0 =A0 =A0 }=0A= =0A= =0A= =0A= =0A= From: Chris Lesiak =0A= Sent: Wednesday, December 23, 2020 7:39 PM=0A= To: Linus Walleij ; Jean Delvare ; Guenter Roeck =0A= Cc: linux-hwmon@vger.kernel.org ; Peter Rosin = ; Jonathan Cameron ; linux-iio@vger.kerne= l.org =0A= Subject: Re: [PATCH v2] hwmon: (ntc_thermistor): try reading processed =0A= =A0=0A= Please don't use iio_read_channel_processed and convert from milliVolts to= =0A= microVolts by multiplying by 1000.=A0 My use case requires the additional= =0A= precision that iio_read_channel_raw followed by iio_convert_raw_to_processe= d=0A= with the 1000X scaler provides.=0A= =0A= But I'm unsure about keeping the fallback 12-bit ADC in place.=A0 I kept it= so as=0A= not to break Naveen Krishna Chatradhi's use case.=A0 But I'm not sure it st= ill works=0A= after commit adc8ec5ff183d09ae7a9d2dd31125401d302ba63=0A= "iio: inkern: pass through raw values if no scaling".=A0 Before the commit,= =0A= iio_convert_raw_to_processed returned a negative number if there was no=0A= scaling available.=A0 Now, it returns the raw value.=0A= Does that mean that the raw value is already scaled to the correct units?= =0A= Or does that mean that the scale is unknown and all you get is counts?=