From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752909Ab2IHJ3u (ORCPT ); Sat, 8 Sep 2012 05:29:50 -0400 Received: from saturn.retrosnub.co.uk ([178.18.118.26]:46957 "EHLO saturn.retrosnub.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752647Ab2IHJ3F (ORCPT ); Sat, 8 Sep 2012 05:29:05 -0400 Message-ID: <504B0FDF.70004@kernel.org> Date: Sat, 08 Sep 2012 10:29:03 +0100 From: Jonathan Cameron User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Bryan Freed CC: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, grundler@chromium.org, ldewangan@nvidia.com, lars@metafoo.de, gregkh@linuxfoundation.org, jic23@cam.ac.uk Subject: Re: [PATCH] iio: isl29018: Support fractional ALS scaling. References: <1346874953-22353-1-git-send-email-bfreed@chromium.org> In-Reply-To: <1346874953-22353-1-git-send-email-bfreed@chromium.org> X-Enigmail-Version: 1.4.3 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/2012 08:55 PM, Bryan Freed wrote: > The Industrial IO framework supports scaling ADC values by fractions, > but most drivers default to using whole numbers. > This change turns on fractional scaling in the isl29018 driver. > > Signed-off-by: Bryan Freed add to togreg branch of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git Thanks Technically doing integer + micro values is actually pretty common but having calibration scale is less so. Doesn't seem any harm in doing it here, though as calibscale is of an arbitary scaling itself, if it wasn't an abi change (which this is not) then I'd suggest just doing it as a 1000 * the original value. Still this does the job nicely so thanks! Jonathan > --- > drivers/staging/iio/light/isl29018.c | 17 +++++++++++++++-- > 1 files changed, 15 insertions(+), 2 deletions(-) > > diff --git a/drivers/staging/iio/light/isl29018.c b/drivers/staging/iio/light/isl29018.c > index 31d22f5..6ee5567 100644 > --- a/drivers/staging/iio/light/isl29018.c > +++ b/drivers/staging/iio/light/isl29018.c > @@ -63,6 +63,7 @@ struct isl29018_chip { > struct regmap *regmap; > struct mutex lock; > unsigned int lux_scale; > + unsigned int lux_uscale; > unsigned int range; > unsigned int adc_bit; > int prox_scheme; > @@ -145,13 +146,22 @@ static int isl29018_read_sensor_input(struct isl29018_chip *chip, int mode) > static int isl29018_read_lux(struct isl29018_chip *chip, int *lux) > { > int lux_data; > + unsigned int data_x_range, lux_unshifted; > > lux_data = isl29018_read_sensor_input(chip, COMMMAND1_OPMODE_ALS_ONCE); > > if (lux_data < 0) > return lux_data; > > - *lux = (lux_data * chip->range * chip->lux_scale) >> chip->adc_bit; > + /* To support fractional scaling, separate the unshifted lux > + * into two calculations: int scaling and micro-scaling. > + * lux_uscale ranges from 0-999999, so about 20 bits. Split > + * the /1,000,000 in two to reduce the risk of over/underflow. > + */ > + data_x_range = lux_data * chip->range; > + lux_unshifted = data_x_range * chip->lux_scale; > + lux_unshifted += data_x_range / 1000 * chip->lux_uscale / 1000; > + *lux = lux_unshifted >> chip->adc_bit; > > return 0; > } > @@ -339,6 +349,8 @@ static int isl29018_write_raw(struct iio_dev *indio_dev, > mutex_lock(&chip->lock); > if (mask == IIO_CHAN_INFO_CALIBSCALE && chan->type == IIO_LIGHT) { > chip->lux_scale = val; > + /* With no write_raw_get_fmt(), val2 is a MICRO fraction. */ > + chip->lux_uscale = val2; > ret = 0; > } > mutex_unlock(&chip->lock); > @@ -379,7 +391,8 @@ static int isl29018_read_raw(struct iio_dev *indio_dev, > case IIO_CHAN_INFO_CALIBSCALE: > if (chan->type == IIO_LIGHT) { > *val = chip->lux_scale; > - ret = IIO_VAL_INT; > + *val2 = chip->lux_uscale; > + ret = IIO_VAL_INT_PLUS_MICRO; > } > break; > default: >