linux-kernel - Re: [PATCH v3 6/8] iio: gyro: bmg160: optimize i2c transfers in trigger handler

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Date:	Fri, 10 Jul 2015 17:46:35 +0000
From:	"Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
To:	"Tirdea, Irina" <irina.tirdea@...el.com>
CC:	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pmeerw@...erw.net" <pmeerw@...erw.net>,
	"jic23@...nel.org" <jic23@...nel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH v3 6/8] iio: gyro: bmg160: optimize i2c transfers in
 trigger handler

On Fri, 2015-07-10 at 17:31 +0000, Tirdea, Irina wrote:
> 
> > -----Original Message-----
> > From: Jonathan Cameron [mailto:jic23@...nel.org]
> > Sent: 05 July, 2015 15:08
> > To: Tirdea, Irina; Wolfram Sang; linux-iio@...r.kernel.org; linux-i2c@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org; Pandruvada, Srinivas; Peter Meerwald
> > Subject: Re: [PATCH v3 6/8] iio: gyro: bmg160: optimize i2c transfers in trigger handler
> > 
> > On 03/07/15 10:33, Irina Tirdea wrote:
> > > Some i2c busses (e.g.: Synopsys DesignWare I2C adapter) need to
> > > enable/disable the bus at each i2c transfer and must wait for
> > > the enable/disable to happen before sending the data.
> > >
> > > When reading data in the trigger handler, the bmg160 driver does
> > > one i2c transfer for each axis. This has an impact on the frequency
> > > of the gyroscope at high sample rates due to additional delays
> > > introduced by the i2c bus at each transfer.
> > >
> > > Reading all axis values in one i2c transfer reduces the delays
> > > introduced by the i2c bus. Uses i2c_smbus_read_i2c_block_data_or_emulated
> > > that will fallback to reading each axis as a separate word in case i2c
> > > block read is not supported.
> > >
> > > Signed-off-by: Irina Tirdea <irina.tirdea@...el.com>
> > Acked-by: Jonathan Cameron <jic23@...nel.org>
> > 
> 
> Thanks Jonathan!
> 
> > Obviously you'll ideally pick up Ack's from the driver authors /maintainers
> > as well.
> > 
> 
> Srinivas, are you OK with these changes for bmc150, bmg160 and kxcjk-1013?
> 
Yes.

Acked-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>

> Thanks,
> Irina
> 
> > Jonathan
> > > ---
> > >  drivers/iio/gyro/bmg160.c | 18 ++++++++----------
> > >  1 file changed, 8 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/iio/gyro/bmg160.c b/drivers/iio/gyro/bmg160.c
> > > index 4b423f2..04e15e9 100644
> > > --- a/drivers/iio/gyro/bmg160.c
> > > +++ b/drivers/iio/gyro/bmg160.c
> > > @@ -784,6 +784,7 @@ static const struct iio_event_spec bmg160_event = {
> > >  		.sign = 's',						\
> > >  		.realbits = 16,					\
> > >  		.storagebits = 16,					\
> > > +		.endianness = IIO_LE,					\
> > >  	},								\
> > >  	.event_spec = &bmg160_event,					\
> > >  	.num_event_specs = 1						\
> > > @@ -822,19 +823,16 @@ static irqreturn_t bmg160_trigger_handler(int irq, void *p)
> > >  	struct iio_poll_func *pf = p;
> > >  	struct iio_dev *indio_dev = pf->indio_dev;
> > >  	struct bmg160_data *data = iio_priv(indio_dev);
> > > -	int bit, ret, i = 0;
> > > +	int ret = 0;
> > >
> > >  	mutex_lock(&data->mutex);
> > > -	for (bit = 0; bit < AXIS_MAX; bit++) {
> > > -		ret = i2c_smbus_read_word_data(data->client,
> > > -					       BMG160_AXIS_TO_REG(bit));
> > > -		if (ret < 0) {
> > > -			mutex_unlock(&data->mutex);
> > > -			goto err;
> > > -		}
> > > -		data->buffer[i++] = ret;
> > > -	}
> > > +	ret = i2c_smbus_read_i2c_block_data_or_emulated(data->client,
> > > +							BMG160_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);
> > >
>