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

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Message-ID: <20170818075552.225551a2@archlinux>
Date:   Fri, 18 Aug 2017 07:56:05 +0100
From:   Jonathan Cameron <jic23@...nel.org>
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 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.

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");