linux-kernel - Re: [PATCH v2 2/2] ti-adc081c: Initial triggered buffer support

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Date:	Sun, 10 Apr 2016 15:29:07 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Crestez Dan Leonard <leonard.crestez@...el.com>,
	linux-iio@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald-Stadler <pmeerw@...erw.net>,
	Daniel Baluta <daniel.baluta@...el.com>
Subject: Re: [PATCH v2 2/2] ti-adc081c: Initial triggered buffer support

On 04/04/16 19:21, Crestez Dan Leonard wrote:
> Using this requires software triggers like CONFIG_IIO_HRTIMER_TRIGGER.
> 
> The device can be configured to do internal periodic sampling but does not
> offer some sort of interrupt on data ready. Interrupts can only trigger when
> values get out of a specific range.
> 
> Signed-off-by: Crestez Dan Leonard <leonard.crestez@...el.com>
basically fine, but just use a fixed size allocation for your buffer in the
trigger handler.
> ---
>  drivers/iio/adc/ti-adc081c.c | 63 +++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 54 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-adc081c.c b/drivers/iio/adc/ti-adc081c.c
> index 3b3c656..d024df2 100644
> --- a/drivers/iio/adc/ti-adc081c.c
> +++ b/drivers/iio/adc/ti-adc081c.c
> @@ -24,6 +24,9 @@
>  #include <linux/of.h>
>  
>  #include <linux/iio/iio.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
>  #include <linux/regulator/consumer.h>
>  
>  struct adc081c {
> @@ -69,18 +72,31 @@ static int adc081c_read_raw(struct iio_dev *iio,
>  	return -EINVAL;
>  }
>  
> -static const struct iio_chan_spec adc081c_channel = {
> -	.type = IIO_VOLTAGE,
> -	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
> -	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> -};
> +#define ADCxx1C_CHAN(_bits) {					\
> +	.type = IIO_VOLTAGE,					\
> +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +	.scan_type = {						\
> +		.sign = 'u',					\
> +		.realbits = (_bits),				\
> +		.storagebits = 16,				\
> +		.shift = 12 - (_bits),				\
> +		.endianness = IIO_CPU,				\
> +	},							\
> +}
>  
>  struct adcxx1c_model {
> +	const struct iio_chan_spec* channels;
>  	int bits;
>  };
>  
>  #define DEFINE_ADCxx1C_MODEL(_name, _bits)				\
> +	static const struct iio_chan_spec _name ## _channels[] = {	\
> +		ADCxx1C_CHAN((_bits)),					\
> +		IIO_CHAN_SOFT_TIMESTAMP(1),				\
> +	};								\
>  	static const struct adcxx1c_model _name ## _model = {		\
> +		.channels = _name ## _channels,				\
>  		.bits = (_bits),					\
>  	}
>  
> @@ -88,11 +104,31 @@ DEFINE_ADCxx1C_MODEL(adc081c,  8);
>  DEFINE_ADCxx1C_MODEL(adc101c, 10);
>  DEFINE_ADCxx1C_MODEL(adc121c, 12);
>  
> +#define ADC081C_NUM_CHANNELS 2
> +
>  static const struct iio_info adc081c_info = {
>  	.read_raw = adc081c_read_raw,
>  	.driver_module = THIS_MODULE,
>  };
>  
> +static irqreturn_t adc081c_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct adc081c *data = iio_priv(indio_dev);
> +	u16 buf[indio_dev->scan_bytes / 2];
Just use a fixed size that is beig enough for whatever you may
get.  Here you need room for a word + an aligned 8 byte timestamp
so 16 bytes, or 8 u16s.  It's not variable so don't let the compiler think
it is.

Also you shouldn't be accessing indio_dev->scan_bytes directly in a driver.
A long time back we spent a while pulling that idiom out of drivers as it
was causing a lot more trouble than the convenience was worth (can't
actually recall why now though!)
> +	int ret;
> +
> +	ret = i2c_smbus_read_word_swapped(data->i2c, REG_CONV_RES);
> +	if (ret < 0)
> +		goto out;
> +	buf[0] = ret;
> +	iio_push_to_buffers_with_timestamp(indio_dev, buf, iio_get_time_ns());
> +out:
> +	iio_trigger_notify_done(indio_dev->trig);
> +	return IRQ_HANDLED;
> +}
> +
>  static int adc081c_probe(struct i2c_client *client,
>  			 const struct i2c_device_id *id)
>  {
> @@ -125,18 +161,26 @@ static int adc081c_probe(struct i2c_client *client,
>  	iio->modes = INDIO_DIRECT_MODE;
>  	iio->info = &adc081c_info;
>  
> -	iio->channels = &adc081c_channel;
> -	iio->num_channels = 1;
> +	iio->channels = model->channels;
> +	iio->num_channels = ADC081C_NUM_CHANNELS;
I'm not sure the define adds anything here!  Kind of obvious what 2 means anyway -
rather than it being a magic number :)
> +
> +	err = iio_triggered_buffer_setup(iio, NULL, adc081c_trigger_handler, NULL);
> +	if (err < 0) {
> +		dev_err(&client->dev, "iio triggered buffer setup failed\n");
> +		goto err_regulator_disable;
> +	}
>  
>  	err = iio_device_register(iio);
>  	if (err < 0)
> -		goto regulator_disable;
> +		goto err_buffer_cleanup;
>  
>  	i2c_set_clientdata(client, iio);
>  
>  	return 0;
>  
> -regulator_disable:
> +err_buffer_cleanup:
> +	iio_triggered_buffer_cleanup(iio);
> +err_regulator_disable:
>  	regulator_disable(adc->ref);
>  
>  	return err;
> @@ -148,6 +192,7 @@ static int adc081c_remove(struct i2c_client *client)
>  	struct adc081c *adc = iio_priv(iio);
>  
>  	iio_device_unregister(iio);
> +	iio_triggered_buffer_cleanup(iio);
>  	regulator_disable(adc->ref);
>  
>  	return 0;
>