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

[Tirdea, Irina]

> -----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!

> > +	}
> > +	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)
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