From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751834AbdKYUtY (ORCPT ); Sat, 25 Nov 2017 15:49:24 -0500 Received: from mail-out-1.itc.rwth-aachen.de ([134.130.5.46]:12381 "EHLO mail-out-1.itc.rwth-aachen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750819AbdKYUtW (ORCPT ); Sat, 25 Nov 2017 15:49:22 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: =?us-ascii?q?A2ASBACk1hla/54agoZbHAEBAQQBAQoBA?= =?us-ascii?q?YM8gXsHnymNTIsyBwOFOwKEXkMUAQEBAQEBAQEBayiFIAEFeRALDgoJJQ8BRwY?= =?us-ascii?q?OBYoiBKhMinoBAQEHAQEBASQJAYMwggeGaYUAEYYDBYhUiW+QA4EOik6VMIdOl?= =?us-ascii?q?g0CAgICCQIagTo2IoFQcIJ2hFZ2iVIBgRMBAQE?= X-IPAS-Result: =?us-ascii?q?A2ASBACk1hla/54agoZbHAEBAQQBAQoBAYM8gXsHnymNTIs?= =?us-ascii?q?yBwOFOwKEXkMUAQEBAQEBAQEBayiFIAEFeRALDgoJJQ8BRwYOBYoiBKhMinoBA?= =?us-ascii?q?QEHAQEBASQJAYMwggeGaYUAEYYDBYhUiW+QA4EOik6VMIdOlg0CAgICCQIagTo?= =?us-ascii?q?2IoFQcIJ2hFZ2iVIBgRMBAQE?= X-IronPort-AV: E=Sophos;i="5.44,455,1505772000"; d="asc'?scan'208";a="25684836" From: Stefan =?ISO-8859-1?Q?Br=FCns?= To: Guenter Roeck CC: Maciej Purski , Jonathan Cameron , , , , Javier Martinez Canillas , Peter Meerwald-Stadler , Lars-Peter Clausen , Hartmut Knaack , "Jean Delvare" , Marek Szyprowski , Bartlomiej Zolnierkiewicz Subject: Re: [PATCH 2/2] hwmon: (ina2xx) Make calibration register value fixed Date: Sat, 25 Nov 2017 21:49:14 +0100 Message-ID: <1765425.OcFVFKOaMc@pebbles> In-Reply-To: <90ceee91-de0e-456f-b0c9-9274973ac02b@roeck-us.net> References: <1511364735-16818-1-git-send-email-m.purski@samsung.com> <1511364735-16818-3-git-send-email-m.purski@samsung.com> <90ceee91-de0e-456f-b0c9-9274973ac02b@roeck-us.net> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart2485776.OalhKULJmM"; micalg=pgp-sha1; protocol="application/pgp-signature" X-Originating-IP: [77.181.53.147] X-ClientProxiedBy: rwthex-s3-b.rwth-ad.de (2002:8682:1aa1::8682:1aa1) To rwthex-w2-a.rwth-ad.de (2002:8682:1a9e::8682:1a9e) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --nextPart2485776.OalhKULJmM Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="iso-8859-1" On Saturday, November 25, 2017 7:50:16 PM CET Guenter Roeck wrote: > On 11/22/2017 07:32 AM, Maciej Purski wrote: > > Calibration register is used for calculating current register in > > hardware according to datasheet: > > current =3D shunt_volt * calib_register / 2048 (ina 226) > > current =3D shunt_volt * calib_register / 4096 (ina 219) > >=20 > > Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in > > order to avoid truncation error and provide best precision allowed > > by shunt_voltage measurement. Make current scale value follow changes > > of shunt_resistor from sysfs as calib_register value is now fixed. > >=20 > > Power_lsb value should also follow shunt_resistor changes as stated in > > datasheet: > > power_lsb =3D 25 * current_lsb (ina 226) > > power_lsb =3D 20 * current_lsb (ina 219) > >=20 > > Signed-off-by: Maciej Purski >=20 > Setting the calibration register to a specific value may optimize precisi= on, > but limits the supported value range, which is the whole point of providi= ng > a calibration register. What am I missing here ? =46or the current register, any different calibration register value is=20 completely useless - smaller values just truncate the register value, large= r=20 values adds noise in the lsbs. Both registers (current/shunt voltage) are=20 16bit, and nothing is going to change that. There is a *very* small allowed power operating area where scaling down wou= ld=20 be of any use: 1. Bus voltage exceeds 25 (20) Volts 2. Shunt voltage is about 82 (320) mV In this case the power register overflows. More specifically, if: (shunt_voltage [mv] / 81.92) * (bus_voltage [V] / 25) > 1 Maximum allowed bus voltage is 36 V resp 26 V. (ina226/219). Kind regards, Stefan =2D-=20 Stefan Br=FCns / Bergstra=DFe 21 / 52062 Aachen home: +49 241 53809034 mobile: +49 151 50412019 --nextPart2485776.OalhKULJmM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part. Content-Transfer-Encoding: 7Bit -----BEGIN PGP SIGNATURE----- iF0EABECAB0WIQSwWRWIpJbl0W4DemNvf0o9jP6qUwUCWhnXSgAKCRBvf0o9jP6q U3niAJ456l1DjlwQN8qLbPTSZl0MxB526gCgrxpT9ghjxcdywvODHcUg/B4+kYA= =9aEm -----END PGP SIGNATURE----- --nextPart2485776.OalhKULJmM--