From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <5390A412.8070401@linux.intel.com> Date: Thu, 05 Jun 2014 10:08:34 -0700 From: Srinivas Pandruvada MIME-Version: 1.0 To: Peter Meerwald CC: linux-iio@vger.kernel.org, jic23@kernel.org Subject: Re: [PATCH] iio: Fix endianness issue in ak8975_read_axis() References: <1401958410-21183-1-git-send-email-pmeerw@pmeerw.net> In-Reply-To: <1401958410-21183-1-git-send-email-pmeerw@pmeerw.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed List-ID: On 06/05/2014 01:53 AM, Peter Meerwald wrote: > i2c_smbus_read_word_data() does host endian conversion already, > no need for le16_to_cpu() > > Signed-off-by: Peter Meerwald > --- > drivers/iio/magnetometer/ak8975.c | 9 +-------- > 1 file changed, 1 insertion(+), 8 deletions(-) > > diff --git a/drivers/iio/magnetometer/ak8975.c b/drivers/iio/magnetometer/ak8975.c > index 09ea5c4..ea08313 100644 > --- a/drivers/iio/magnetometer/ak8975.c > +++ b/drivers/iio/magnetometer/ak8975.c > @@ -373,8 +373,6 @@ static int ak8975_read_axis(struct iio_dev *indio_dev, int index, int *val) > { > struct ak8975_data *data = iio_priv(indio_dev); > struct i2c_client *client = data->client; > - u16 meas_reg; > - s16 raw; > int ret; > > mutex_lock(&data->lock); > @@ -422,16 +420,11 @@ static int ak8975_read_axis(struct iio_dev *indio_dev, int index, int *val) > dev_err(&client->dev, "Read axis data fails\n"); > goto exit; > } > - meas_reg = ret; > > mutex_unlock(&data->lock); > > - /* Endian conversion of the measured values. */ > - raw = (s16) (le16_to_cpu(meas_reg)); > - > /* Clamp to valid range. */ > - raw = clamp_t(s16, raw, -4096, 4095); > - *val = raw; > + *val = clamp_t(s16, ret, -4096, 4095); > return IIO_VAL_INT; > > exit: > I did some experiments on little-endian platforms, so your change won't hurt on x86. Read as word data -> Reg 3 (LB) and Reg 4(HB) [ 1529.699617] Word read reg->3:ffc8 Read as byte separately LB and HB [ 1529.711619] Byte read reg->3:c8 reg->4:ff x86 platform is le, so no change in output by call to le16_to_cpu [ 1529.711634] Raw value final ffffffc8 Don't we need to convert for big-endian platforms? When I trace the path for i2c, I don't see any host order conversion. Path: i2c_smbus_read_word_data->i2c_smbus_xfer->i2c_smbus_xfer_emulated i2c_smbus_xfer_emulated { (for designware) bus // Send command part adap->algo->master_xfer->i2c_dw_xfer_msg -> // Rx data via i2c_dw_read, don't see any host order conversion \ { order word according to SMBUS specification, low byte on the bus first case I2C_SMBUS_WORD_DATA: case I2C_SMBUS_PROC_CALL: data->word = msgbuf1[0] | (msgbuf1[1] << 8); break; } But there is no host order conversion? } Thanks, Srinivas