linux-kernel - Re: [PATCH 4/6] iio: accel: bmg160: optimize transfers in trigger handler

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Date:	Mon, 28 Mar 2016 12:09:29 +0200 (CEST)
From:	Peter Meerwald-Stadler <pmeerw@...erw.net>
To:	Jonathan Cameron <jic23@...nel.org>
cc:	Irina Tirdea <irina.tirdea@...el.com>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Octavian Purdila <octavian.purdila@...el.com>,
	Markus Pargmann <mpa@...gutronix.de>,
	Srinivas Pandruvada <srinivas.pandruvada@...el.com>
Subject: Re: [PATCH 4/6] iio: accel: bmg160: optimize transfers in trigger
 handler


> > 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 bmc150 accel driver does

should refer to bmg160

> > one bus transfer for each axis. This has an impact on the frequency
> > of the accelerometer at high sample rates due to additional delays
> > introduced by the bus at each transfer.
> > 
> > Reading all axis values in one bus transfer reduces the delays
> > introduced by the bus.
> > 
> > Signed-off-by: Irina Tirdea <irina.tirdea@...el.com>
> I forgot to highlight on the earlier driver that there is also 'technically'
> a bit of an ABI change here because we are now exporting as LE rather than CPU
> order.  However, I 'hope' anyone actually accessing the buffered data is either
> doing it through a nice library or hasn't hacked the endian unwinding out of
> the generic_buffer example!

the patch takes away the possibility to do buffered reads on individual 
channels (not sure if this is useful per se)

this optimizes for the common case, ok;

wondering if adding 
.endianness = IIO_LE
is actually an unrelated fix

> Again, fingers crossed this doesn't break anything significant.
> 
> Applied,
> 
> Thanks,
> 
> Jonathan
> > ---
> >  drivers/iio/gyro/bmg160_core.c | 17 ++++++-----------
> >  1 file changed, 6 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/iio/gyro/bmg160_core.c b/drivers/iio/gyro/bmg160_core.c
> > index 8d6e5b1..43570b8 100644
> > --- a/drivers/iio/gyro/bmg160_core.c
> > +++ b/drivers/iio/gyro/bmg160_core.c
> > @@ -734,6 +734,7 @@ 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						\
> > @@ -773,20 +774,14 @@ 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;
> > -	unsigned int val;
> > +	int ret;
> >  
> >  	mutex_lock(&data->mutex);
> > -	for (bit = 0; bit < AXIS_MAX; bit++) {
> > -		ret = regmap_bulk_read(data->regmap, BMG160_AXIS_TO_REG(bit),
> > -				       &val, 2);
> > -		if (ret < 0) {
> > -			mutex_unlock(&data->mutex);
> > -			goto err;
> > -		}
> > -		data->buffer[i++] = ret;
> > -	}
> > +	ret = regmap_bulk_read(data->regmap, BMG160_REG_XOUT_L,
> > +			       data->buffer, AXIS_MAX * 2);
> >  	mutex_unlock(&data->mutex);
> > +	if (ret < 0)
> > +		goto err;
> >  
> >  	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> >  					   pf->timestamp);
> > 
> 

-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)