From patchwork Wed Mar 13 11:40:02 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Enric Balletbo i Serra X-Patchwork-Id: 10851007 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id AB3DC6C2 for ; Wed, 13 Mar 2019 11:40:13 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 88B9E29AE8 for ; Wed, 13 Mar 2019 11:40:13 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 86EE229B4A; Wed, 13 Mar 2019 11:40:13 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI,UNPARSEABLE_RELAY autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 3299329AE8 for ; Wed, 13 Mar 2019 11:40:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725889AbfCMLkL (ORCPT ); Wed, 13 Mar 2019 07:40:11 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:35472 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725888AbfCMLkL (ORCPT ); Wed, 13 Mar 2019 07:40:11 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: eballetbo) with ESMTPSA id CAEEF27FD1A From: Enric Balletbo i Serra To: Jonathan Cameron , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Gwendal Grignou , Peter Meerwald-Stadler , Guenter Roeck , Benson Leung , Lars-Peter Clausen , kernel@collabora.com, Hartmut Knaack Subject: [PATCH v3] iio: cros_ec: Fix the maths for gyro scale calculation Date: Wed, 13 Mar 2019 12:40:02 +0100 Message-Id: <20190313114002.11236-1-enric.balletbo@collabora.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Sender: linux-iio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Gwendal Grignou Calculation did not use IIO_DEGREE_TO_RAD and implemented a variant to avoid precision loss as we aim a nano value. The offset added to avoid rounding error, though, doesn't give us a close result to the expected value. E.g. For 1000dps, the result should be: (1000 * pi ) / 180 >> 15 ~= 0.000532632218 But with current calculation we get $ cat scale 0.000547890 Fix the calculation by just doing the maths involved for a nano value val * pi * 10e12 / (180 * 2^15) so we get a closer result. $ cat scale 0.000532632 Fixes: c14dca07a31d ("iio: cros_ec_sensors: add ChromeOS EC Contiguous Sensors driver") Signed-off-by: Gwendal Grignou Signed-off-by: Enric Balletbo i Serra --- Changes in v3: - Fix 'warning: this decimal constant is unsigned only in ISO C90' spotted by kbuild test robot. Changes in v2: - Do the maths instead of play with dividers as pointed by Jonathan. drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c index 89cb0066a6e0..8d76afb87d87 100644 --- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c +++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c @@ -103,9 +103,10 @@ static int cros_ec_sensors_read(struct iio_dev *indio_dev, * Do not use IIO_DEGREE_TO_RAD to avoid precision * loss. Round to the nearest integer. */ - *val = div_s64(val64 * 314159 + 9000000ULL, 1000); - *val2 = 18000 << (CROS_EC_SENSOR_BITS - 1); - ret = IIO_VAL_FRACTIONAL; + *val = 0; + *val2 = div_s64(val64 * 3141592653ULL, + 180 << (CROS_EC_SENSOR_BITS - 1)); + ret = IIO_VAL_INT_PLUS_NANO; break; case MOTIONSENSE_TYPE_MAG: /*