From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from saturn.retrosnub.co.uk ([178.18.118.26]:37208 "EHLO saturn.retrosnub.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755936AbbI0PjJ (ORCPT ); Sun, 27 Sep 2015 11:39:09 -0400 Subject: Re: [PATCH] iio: chemical: vz89x hardware i2c workaround To: Matt Ranostay , lars@metafoo.de, pmeerw@pmeerw.net References: <1442982309-3925-1-git-send-email-mranostay@gmail.com> Cc: linux-iio@vger.kernel.org From: Jonathan Cameron Message-ID: <56080D9B.9040905@kernel.org> Date: Sun, 27 Sep 2015 16:39:07 +0100 MIME-Version: 1.0 In-Reply-To: <1442982309-3925-1-git-send-email-mranostay@gmail.com> Content-Type: text/plain; charset=windows-1252 Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On 23/09/15 05:25, Matt Ranostay wrote: > Chipset sometime updates in the middle of a reading causing it > to reset the data pointer, and causing invalid reading of previous data. > > We can check for this invalid state by reading MSB of the resistance > reading that is always zero, and by also confirming the VOC_short isn't > zero. > > Signed-off-by: Matt Ranostay Applied. > --- > drivers/iio/chemical/vz89x.c | 23 +++++++++++++++++++++-- > 1 file changed, 21 insertions(+), 2 deletions(-) > > diff --git a/drivers/iio/chemical/vz89x.c b/drivers/iio/chemical/vz89x.c > index b454200..11e59a5 100644 > --- a/drivers/iio/chemical/vz89x.c > +++ b/drivers/iio/chemical/vz89x.c > @@ -85,6 +85,21 @@ static const struct attribute_group vz89x_attrs_group = { > .attrs = vz89x_attributes, > }; > > +/* > + * Chipset sometime updates in the middle of a reading causing it to reset the > + * data pointer, and causing invalid reading of previous data. > + * We can check for this by reading MSB of the resistance reading that is > + * always zero, and by also confirming the VOC_short isn't zero. > + */ > + > +static int vz89x_measurement_is_valid(struct vz89x_data *data) > +{ > + if (data->buffer[VZ89X_VOC_SHORT_IDX] == 0) > + return 1; > + > + return !!(data->buffer[VZ89X_REG_MEASUREMENT_SIZE - 1] > 0); > +} > + > static int vz89x_get_measurement(struct vz89x_data *data) > { > int ret; > @@ -106,6 +121,10 @@ static int vz89x_get_measurement(struct vz89x_data *data) > data->buffer[i] = ret; > } > > + ret = vz89x_measurement_is_valid(data); > + if (ret) > + return -EAGAIN; > + > data->last_update = jiffies; > > return 0; > @@ -113,9 +132,9 @@ static int vz89x_get_measurement(struct vz89x_data *data) > > static int vz89x_get_resistance_reading(struct vz89x_data *data) > { > - u8 *buf = &data->buffer[VZ89X_VOC_TVOC_IDX]; > + u8 *buf = &data->buffer[VZ89X_VOC_RESISTANCE_IDX]; > > - return buf[0] | (buf[1] << 8) | (buf[2] << 16); > + return buf[0] | (buf[1] << 8); > } > > static int vz89x_read_raw(struct iio_dev *indio_dev, >