Re: [PATCH 2/2] iio: accel: kxcjk-1013: optimize i2c transfers in trigger handler

[Pandruvada, Srinivas]

On Fri, 2015-02-20 at 12:02 +0000, Tirdea, Irina wrote:
> 
> > -----Original Message-----
> > From: Peter Meerwald [mailto:pmeerw@xxxxxxxxxx]
> > Sent: 16 February, 2015 21:26
> > To: Tirdea, Irina
> > Cc: Jonathan Cameron; linux-iio@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Pandruvada, Srinivas; Reus, Adriana
> > Subject: Re: [PATCH 2/2] iio: accel: kxcjk-1013: optimize i2c transfers in trigger handler
> > 
> > 
> > > Reading all axis values in one i2c transfer reduces the delays
> > > introduced by the i2c bus. In case i2c block read is not supported,
> > > fallback to reading each axis as a separate word.
> > 
> > see comments inline below
> > 
> Thanks for the review, Peter!
> 
> > > Signed-off-by: Adriana Reus <adriana.reus@xxxxxxxxx>
> > > Signed-off-by: Irina Tirdea <irina.tirdea@xxxxxxxxx>
> > > Reviewed-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> > > ---
> > >  drivers/iio/accel/kxcjk-1013.c | 44 +++++++++++++++++++++++++++++++++---------
> > >  1 file changed, 35 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/iio/accel/kxcjk-1013.c b/drivers/iio/accel/kxcjk-1013.c
> > > index 5f27787..bfa2899 100644
> > > --- a/drivers/iio/accel/kxcjk-1013.c
> > > +++ b/drivers/iio/accel/kxcjk-1013.c
> > > @@ -109,6 +109,8 @@ struct kxcjk1013_data {
> > >  	int64_t timestamp;
> > >  	enum kx_chipset chipset;
> > >  	bool is_smo8500_device;
> > > +	s32 (*read_block_data)(const struct i2c_client *client, u8 command,
> > > +			       u8 length, u8 *values);
> > 
> > probably this could/should be done in the i2c layer or we end up adding a
> > similar function in every driver?
> > 
> Actually this is exactly what I did: adding this code in a couple of drivers :)
> You are right, this belongs to the i2c core. Will move it there.
> 
> > >  };
> > >
> > >  enum kxcjk1013_axis {
> > > @@ -216,6 +218,23 @@ static const struct {
> > >  				 {800, 0, 0x06},
> > >  				 {1600, 0, 0x06} };
> > >
> > > +static s32 kxcjk1013_read_block_data(const struct i2c_client *client,
> > > +				     u8 command, u8 length, u8 *values)
> > > +{
> > > +	s32 data;
> > > +	u8 i;
> > > +
> > > +	for (i = 0; i < length; i += 2) {
> > > +		data = i2c_smbus_read_word_data(client, command + i);
> > > +		if (data < 0)
> > > +			return data;
> > > +
> > > +		values[i] = data & 0xFF;
> > > +		values[i+1] = data >> 8;
> > 
> > this is incorrect; it forces the data to be little endian, however, the
> > endianness (as specified in the driver's .scan_type) is IIO_CPU -- the
> > code breaks for big-endian CPUs
> > 
> > since _read_i2c_block_data() can't do endianness conversion (and the chip
> > does i2c endianness, i.e. little-endian), the .scan_type should become
> > IIO_LE and above code is correct again but still ugly :)
> > 
> > bottom line: change .scan_type to IIO_LE
> > 
> Good point. Changing the endianess to IIO_LE is correct for either kxcjk1013_read_block_data or i2c_smbus_read_i2c_block_data.
> Will fix this in the next version. Thanks for catching this!
> 
I don't think changing to IIO_LE is good idea as when i2c_read_bock..
then the scan type will be CPU. So better to fix endianness in this
function.

> > > +	}
> > > +	return i;
> > > +}
> > > +
> > >  static int kxcjk1013_set_mode(struct kxcjk1013_data *data,
> > >  			      enum kxcjk1013_mode mode)
> > >  {
> > > @@ -955,18 +974,14 @@ static irqreturn_t kxcjk1013_trigger_handler(int irq, void *p)
> > >  	struct iio_poll_func *pf = p;
> > >  	struct iio_dev *indio_dev = pf->indio_dev;
> > >  	struct kxcjk1013_data *data = iio_priv(indio_dev);
> > > -	int bit, ret, i = 0;
> > > +	int ret;
> > >
> > >  	mutex_lock(&data->mutex);
> > > -	for (bit = 0; bit < AXIS_MAX; bit++) {
> > > -		ret = kxcjk1013_get_acc_reg(data, bit);
> > > -		if (ret < 0) {
> > > -			mutex_unlock(&data->mutex);
> > > -			goto err;
> > > -		}
> > > -		data->buffer[i++] = ret;
> > > -	}
> > > +	ret = data->read_block_data(data->client, KXCJK1013_REG_XOUT_L,
> > > +				    AXIS_MAX * 2, (u8 *) data->buffer);
> > >  	mutex_unlock(&data->mutex);
> > > +	if (ret < 0)
> > > +		goto err;
> > >
> > >  	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> > >  					   data->timestamp);
> > > @@ -1196,6 +1211,11 @@ static int kxcjk1013_probe(struct i2c_client *client,
> > >  	const char *name;
> > >  	int ret;
> > >
> > > +	if (!i2c_check_functionality(client->adapter,
> > > +				     I2C_FUNC_SMBUS_BYTE_DATA |
> > > +				     I2C_FUNC_SMBUS_READ_WORD_DATA))
> > > +		return -ENODEV;
> > > +
> > >  	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> > >  	if (!indio_dev)
> > >  		return -ENOMEM;
> > > @@ -1204,6 +1224,12 @@ static int kxcjk1013_probe(struct i2c_client *client,
> > >  	i2c_set_clientdata(client, indio_dev);
> > >  	data->client = client;
> > >
> > > +	if (i2c_check_functionality(client->adapter,
> > > +				    I2C_FUNC_SMBUS_READ_I2C_BLOCK))
> > > +		data->read_block_data = i2c_smbus_read_i2c_block_data;
> > > +	else
> > > +		data->read_block_data = kxcjk1013_read_block_data;
> > > +
> > >  	pdata = dev_get_platdata(&client->dev);
> > >  	if (pdata)
> > >  		data->active_high_intr = pdata->active_high_intr;
> > >
> > 
> > --
> > 
> > Peter Meerwald
> > +43-664-2444418 (mobile)