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[85.148.52.161]) by smtp.gmail.com with ESMTPSA id j15sm4094885edj.42.2018.04.20.12.31.11 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 20 Apr 2018 12:31:12 -0700 (PDT) Date: Fri, 20 Apr 2018 21:31:09 +0200 From: David Veenstra To: lars@metafoo.de, jic23@kernel.org, pmeerw@pmeerw.net Cc: robh+dt@kernel.org, Michael.Hennerich@analog.com, knaack.h@gmx.de, daniel.baluta@nxp.com, linux-iio@vger.kernel.org, devel@driverdev.osuosl.org, devicetree@vger.kernel.org Subject: [PATCH v2 10/13] staging: iio: ad2s1200: Add scaling factor for angular velocity channel Message-ID: <752211cc5dd962e9588263d9d3591d2f4d386c26.1524247563.git.davidjulianveenstra@gmail.com> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) 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 The sysfs iio ABI states radians per second is expected as the unit for angular velocity, but the 12-bit angular velocity register has rps as its unit. So a fractional scaling factor of approximately 2 * Pi is added to the angular velocity channel. The added comments will also be relevant for the scaling factor of the angle channel. Signed-off-by: David Veenstra --- Changes in v2: - Move explanation of Pi approximation to top of switch statement, as this will also be relevant to angle channel. - Replaced 33102 / 2 with 16551 on line 84. drivers/staging/iio/resolver/ad2s1200.c | 84 +++++++++++++++++++++++---------- 1 file changed, 59 insertions(+), 25 deletions(-) diff --git a/drivers/staging/iio/resolver/ad2s1200.c b/drivers/staging/iio/resolver/ad2s1200.c index 29a9bb666e7b..6c56257be3b1 100644 --- a/drivers/staging/iio/resolver/ad2s1200.c +++ b/drivers/staging/iio/resolver/ad2s1200.c @@ -60,38 +60,71 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev, int ret = 0; u16 vel; - mutex_lock(&st->lock); - gpiod_set_value(st->sample, 0); + /* + * Below a fractional approximation of Pi is needed. + * The following approximation will be used: 103993 / 33102. + * This is accurate in 9 decimals places. + * + * This fraction is based on OEIS series of nominator/denominator + * of convergents to Pi (A002485 and A002486). + */ + switch (m) { + case IIO_CHAN_INFO_SCALE: + switch (chan->type) { + case IIO_ANGL_VEL: + /* + * 2 * Pi ~= 2 * 103993 / 33102 + * + * iio_convert_raw_to_processed uses integer + * division. This will cause at most 5% error + * (for very small values). But for 99.5% of the values + * it will cause less that 1% error. + */ + *val = 103993; + *val2 = 16551; + return IIO_VAL_FRACTIONAL; + default: + return -EINVAL; + } + break; + case IIO_CHAN_INFO_RAW: + mutex_lock(&st->lock); + gpiod_set_value(st->sample, 0); + + /* delay (6 * AD2S1200_TSCLK + 20) nano seconds */ + udelay(1); + gpiod_set_value(st->sample, 1); + gpiod_set_value(st->rdvel, !!(chan->type == IIO_ANGL)); + + ret = spi_read(st->sdev, st->rx, 2); + if (ret < 0) { + mutex_unlock(&st->lock); + return ret; + } - /* delay (6 * AD2S1200_TSCLK + 20) nano seconds */ - udelay(1); - gpiod_set_value(st->sample, 1); - gpiod_set_value(st->rdvel, !!(chan->type == IIO_ANGL)); + vel = be16_to_cpup((__be16 *)st->rx); + switch (chan->type) { + case IIO_ANGL: + *val = vel >> 4; + break; + case IIO_ANGL_VEL: + *val = sign_extend32((s16)vel >> 4, 11); + break; + default: + mutex_unlock(&st->lock); + return -EINVAL; + } - ret = spi_read(st->sdev, st->rx, 2); - if (ret < 0) { + /* delay (2 * AD2S1200_TSCLK + 20) ns for sample pulse */ + udelay(1); mutex_unlock(&st->lock); - return ret; - } - vel = be16_to_cpup((__be16 *)st->rx); - switch (chan->type) { - case IIO_ANGL: - *val = vel >> 4; - break; - case IIO_ANGL_VEL: - *val = sign_extend32((s16)vel >> 4, 11); - break; + return IIO_VAL_INT; default: - mutex_unlock(&st->lock); - return -EINVAL; + break; } - /* delay (2 * AD2S1200_TSCLK + 20) ns for sample pulse */ - udelay(1); - mutex_unlock(&st->lock); - - return IIO_VAL_INT; + return -EINVAL; } static const struct iio_chan_spec ad2s1200_channels[] = { @@ -105,6 +138,7 @@ static const struct iio_chan_spec ad2s1200_channels[] = { .indexed = 1, .channel = 0, .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), } };