RE: [PATCH v5 6/8] iio: gyro: bmg160: optimize i2c transfers in trigger handler

[Tirdea, Irina]

> -----Original Message-----
> From: Markus Pargmann [mailto:mpa@xxxxxxxxxxxxxx]
> Sent: 17 August, 2015 12:10
> To: Jonathan Cameron
> Cc: Tirdea, Irina; Wolfram Sang; linux-iio@xxxxxxxxxxxxxxx; linux-i2c@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Pandruvada,
> Srinivas; Peter Meerwald
> Subject: Re: [PATCH v5 6/8] iio: gyro: bmg160: optimize i2c transfers in trigger handler
> 
> On Sun, Aug 16, 2015 at 10:24:47AM +0100, Jonathan Cameron wrote:
> > On 12/08/15 15:31, 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@xxxxxxxxx>
> > > Acked-by: Jonathan Cameron <jic23@xxxxxxxxxx>
> > > Acked-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> > Note, that in the meantime the bmg160 driver just went all regmap
> > on us (as part of adding SPI support - though that step hasn't
> > happened yet).  Hence we'll need a means of telling regmap about this
> > possibility.
> 
> Perhaps this is covered by a regmap_bulk_read()?

I think it is. However, if that does not work for the i2c controllers I'm
testing with I'll take a look at the patches you mention below.
I'll rebase this patch on top of your next version for bmg160 and
resend.

Thanks,
Irina

> 
> The series[1] I am working on implements a i2c smbus block data regmap
> bus driver. Regmap should then automatically do a block read in
> regmap_bulk_read.
> 
> Patch 15 introduces the i2c block data regmap bus driver[2].
> I am only implementing this so I don't break bmc150 behavior. I do not
> have the hardware available to test this regmap driver so it would be great
> if someone else could test one of the next versions of this bus driver.
> 
> Best regards,
> 
> Markus
> 
> [1] http://thread.gmane.org/gmane.linux.kernel/2018643
> [2] http://thread.gmane.org/gmane.linux.kernel/2018639
> 
> >
> > > ---
> > >  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 b2a6ccb..1ff306d 100644
> > > --- a/drivers/iio/gyro/bmg160.c
> > > +++ b/drivers/iio/gyro/bmg160.c
> > > @@ -772,6 +772,7 @@ 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						\
> > > @@ -809,19 +810,16 @@ 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,
> > >  					   pf->timestamp);
> > >
> >
> > --
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