Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932244AbaBTXxr (ORCPT ); Thu, 20 Feb 2014 18:53:47 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:46175 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932225AbaBTXxo (ORCPT ); Thu, 20 Feb 2014 18:53:44 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Beomho Seo , Jonathan Cameron Subject: [PATCH 3.13 56/99] iio: ak8975: Fix calculation formula for convert micro tesla to gauss unit Date: Thu, 20 Feb 2014 15:52:51 -0800 Message-Id: <20140220235119.827060202@linuxfoundation.org> X-Mailer: git-send-email 1.9.0 In-Reply-To: <20140220235118.191692546@linuxfoundation.org> References: <20140220235118.191692546@linuxfoundation.org> User-Agent: quilt/0.61-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.13-stable review patch. If anyone has any objections, please let me know. ------------------ From: Beomho Seo commit bef44abccb2677e8d16e50b75316d4fd1061be81 upstream. This effects the reported scale of the raw values, and thus userspace applications that use this value. One micro tesla equal 0.01 gauss. So I have fixed calculation formula And add RAW_TO_GAUSS macro. ASA is in the range of 0 to 255. If multiply 0.003, calculation result(in_magn_[*]_scale) is always 0. So multiply 3000 and return and IIO_VAL_INT_PLUS_MICRO. As a result, read_raw call back function return accurate scale value. Signed-off-by: Beomho Seo Signed-off-by: Jonathan Cameron Signed-off-by: Greg Kroah-Hartman --- drivers/iio/magnetometer/ak8975.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) --- a/drivers/iio/magnetometer/ak8975.c +++ b/drivers/iio/magnetometer/ak8975.c @@ -85,6 +85,7 @@ #define AK8975_MAX_CONVERSION_TIMEOUT 500 #define AK8975_CONVERSION_DONE_POLL_TIME 10 #define AK8975_DATA_READY_TIMEOUT ((100*HZ)/1000) +#define RAW_TO_GAUSS(asa) ((((asa) + 128) * 3000) / 256) /* * Per-instance context data for the device. @@ -265,15 +266,15 @@ static int ak8975_setup(struct i2c_clien * * Since 1uT = 0.01 gauss, our final scale factor becomes: * - * Hadj = H * ((ASA + 128) / 256) * 3/10 * 100 - * Hadj = H * ((ASA + 128) * 30 / 256 + * Hadj = H * ((ASA + 128) / 256) * 3/10 * 1/100 + * Hadj = H * ((ASA + 128) * 0.003) / 256 * * Since ASA doesn't change, we cache the resultant scale factor into the * device context in ak8975_setup(). */ - data->raw_to_gauss[0] = ((data->asa[0] + 128) * 30) >> 8; - data->raw_to_gauss[1] = ((data->asa[1] + 128) * 30) >> 8; - data->raw_to_gauss[2] = ((data->asa[2] + 128) * 30) >> 8; + data->raw_to_gauss[0] = RAW_TO_GAUSS(data->asa[0]); + data->raw_to_gauss[1] = RAW_TO_GAUSS(data->asa[1]); + data->raw_to_gauss[2] = RAW_TO_GAUSS(data->asa[2]); return 0; } @@ -428,8 +429,9 @@ static int ak8975_read_raw(struct iio_de case IIO_CHAN_INFO_RAW: return ak8975_read_axis(indio_dev, chan->address, val); case IIO_CHAN_INFO_SCALE: - *val = data->raw_to_gauss[chan->address]; - return IIO_VAL_INT; + *val = 0; + *val2 = data->raw_to_gauss[chan->address]; + return IIO_VAL_INT_PLUS_MICRO; } return -EINVAL; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/