linux-kernel - Re: [PATCH v3 3/5] iio: srf08: add triggered buffer support

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Date:   Fri, 18 Aug 2017 08:01:38 +0100
From:   Jonathan Cameron <jic23@...23.retrosnub.co.uk>
To:     Andreas Klinger <ak@...klinger.de>
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        linux-iio@...r.kernel.org, wsa@...-dreams.de, robh+dt@...nel.org,
        mark.rutland@....com, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/5] iio: srf08: add triggered buffer support

On Fri, 18 Aug 2017 07:56:05 +0100
Jonathan Cameron <jic23@...nel.org> wrote:

> On Wed, 16 Aug 2017 21:34:06 +0200
> Andreas Klinger <ak@...klinger.de> wrote:
> 
> > Add support for triggered buffers.
> > 
> > Data format is quite simple:
> >   distance     16 Bit
> >   alignment    48 Bit
> >   timestamp    64 Bit
> > 
> > Signed-off-by: Andreas Klinger <ak@...klinger.de>  
> 
> One little improvement I noticed inline that an additional unlocked
> reading function would tidy up.

Let us treat this as a suggestion for a follow up patch.
It isn't substantial enough to prevent me takin the patch in it's
current state.

Applied to the togreg branch of iio.git and pushed out as testing
for the autobuilders to play with it.

Thanks,

Jonathan
> 
> Thanks,
> 
> Jonathan
> > ---
> >  drivers/iio/proximity/srf08.c | 60 ++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 57 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/iio/proximity/srf08.c b/drivers/iio/proximity/srf08.c
> > index 3f19536f215f..de699d67310a 100644
> > --- a/drivers/iio/proximity/srf08.c
> > +++ b/drivers/iio/proximity/srf08.c
> > @@ -18,6 +18,9 @@
> >  #include <linux/bitops.h>
> >  #include <linux/iio/iio.h>
> >  #include <linux/iio/sysfs.h>
> > +#include <linux/iio/buffer.h>
> > +#include <linux/iio/trigger_consumer.h>
> > +#include <linux/iio/triggered_buffer.h>
> >  
> >  /* registers of SRF08 device */
> >  #define SRF08_WRITE_COMMAND	0x00	/* Command Register */
> > @@ -35,9 +38,22 @@
> >  
> >  struct srf08_data {
> >  	struct i2c_client	*client;
> > -	int			sensitivity;		/* Gain */
> > -	int			range_mm;		/* max. Range in mm */
> > +
> > +	/*
> > +	 * Gain in the datasheet is called sensitivity here to distinct it
> > +	 * from the gain used with amplifiers of adc's
> > +	 */
> > +	int			sensitivity;
> > +
> > +	/* max. Range in mm */
> > +	int			range_mm;
> >  	struct mutex		lock;
> > +
> > +	/*
> > +	 * triggered buffer
> > +	 * 1x16-bit channel + 3x16 padding + 4x16 timestamp
> > +	 */
> > +	s16			buffer[8];
> >  };
> >  
> >  /*
> > @@ -110,6 +126,29 @@ static int srf08_read_ranging(struct srf08_data *data)
> >  	return ret;
> >  }
> >  
> > +static irqreturn_t srf08_trigger_handler(int irq, void *p)
> > +{
> > +	struct iio_poll_func *pf = p;
> > +	struct iio_dev *indio_dev = pf->indio_dev;
> > +	struct srf08_data *data = iio_priv(indio_dev);
> > +	s16 sensor_data;
> > +  
> 
> There is a bit of lock bouncing going on here where you take the lock
> inside srf08_read_ranging drop it at the end and immediately
> retake it.  
> 
> Introduce an unlocked version of read_ranging and hold the lock over
> the whole cycle.
> > +	sensor_data = srf08_read_ranging(data);
> > +	if (sensor_data < 0)
> > +		goto err;
> > +
> > +	mutex_lock(&data->lock);
> > +
> > +	data->buffer[0] = sensor_data;
> > +	iio_push_to_buffers_with_timestamp(indio_dev,
> > +						data->buffer, pf->timestamp);
> > +
> > +	mutex_unlock(&data->lock);
> > +err:
> > +	iio_trigger_notify_done(indio_dev->trig);
> > +	return IRQ_HANDLED;
> > +}
> > +
> >  static int srf08_read_raw(struct iio_dev *indio_dev,
> >  			    struct iio_chan_spec const *channel, int *val,
> >  			    int *val2, long mask)
> > @@ -323,7 +362,15 @@ static const struct iio_chan_spec srf08_channels[] = {
> >  		.info_mask_separate =
> >  				BIT(IIO_CHAN_INFO_RAW) |
> >  				BIT(IIO_CHAN_INFO_SCALE),
> > +		.scan_index = 0,
> > +		.scan_type = {
> > +			.sign = 's',
> > +			.realbits = 16,
> > +			.storagebits = 16,
> > +			.endianness = IIO_CPU,
> > +		},
> >  	},
> > +	IIO_CHAN_SOFT_TIMESTAMP(1),
> >  };
> >  
> >  static const struct iio_info srf08_info = {
> > @@ -362,6 +409,13 @@ static int srf08_probe(struct i2c_client *client,
> >  
> >  	mutex_init(&data->lock);
> >  
> > +	ret = devm_iio_triggered_buffer_setup(&client->dev, indio_dev,
> > +			iio_pollfunc_store_time, srf08_trigger_handler, NULL);
> > +	if (ret < 0) {
> > +		dev_err(&client->dev, "setup of iio triggered buffer failed\n");
> > +		return ret;
> > +	}
> > +
> >  	/*
> >  	 * set default values of device here
> >  	 * these register values cannot be read from the hardware
> > @@ -402,5 +456,5 @@ static struct i2c_driver srf08_driver = {
> >  module_i2c_driver(srf08_driver);
> >  
> >  MODULE_AUTHOR("Andreas Klinger <ak@...klinger.de>");
> > -MODULE_DESCRIPTION("Devantech SRF08 ultrasonic ranger driver");
> > +MODULE_DESCRIPTION("Devantech SRF08/SRF10 ultrasonic ranger driver");
> >  MODULE_LICENSE("GPL");  
> 
> --
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