From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailout1.samsung.com ([203.254.224.24]:37272 "EHLO mailout1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753774AbaBDJQB (ORCPT ); Tue, 4 Feb 2014 04:16:01 -0500 Received: from epcpsbgr5.samsung.com (u145.gpu120.samsung.co.kr [203.254.230.145]) by mailout1.samsung.com (Oracle Communications Messaging Server 7u4-24.01 (7.0.4.24.0) 64bit (built Nov 17 2011)) with ESMTP id <0N0G00DUYSEN2550@mailout1.samsung.com> for linux-iio@vger.kernel.org; Tue, 04 Feb 2014 18:15:59 +0900 (KST) Message-id: <52F0AFCF.1090302@samsung.com> Date: Tue, 04 Feb 2014 18:15:59 +0900 From: Beomho Seo MIME-version: 1.0 To: linux-iio@vger.kernel.org, ldewangan@nvidia.com Cc: Jonathan Cameron , Peter Meerwald , Myungjoo Ham , Jaehoon Chung Subject: [PATCH RESEND 1/2] iio: ak8975: Fix calculation formula for convert micro tesla to gauss unit Content-type: text/plain; charset=ISO-8859-1 Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org 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 --- drivers/iio/magnetometer/ak8975.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/drivers/iio/magnetometer/ak8975.c b/drivers/iio/magnetometer/ak8975.c index ff284e5..0542354 100644 --- 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_client *client) * * 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_dev *indio_dev, 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; } -- 1.7.9.5 -- Best Regards,