linux-kernel - Re: [PATCH v1] iio: adc: add buffering support to the TI LMP92064 ADC driver

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Date:   Sat, 17 Jun 2023 19:27:29 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Leonard Göhrs <l.goehrs@...gutronix.de>
Cc:     kernel@...gutronix.de, Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] iio: adc: add buffering support to the TI LMP92064
 ADC driver

On Wed, 14 Jun 2023 09:55:36 +0200
Leonard Göhrs <l.goehrs@...gutronix.de> wrote:

> Enable buffered reading of samples from the LMP92064 ADC.
> The main benefit of this change is being able to read out current and
> voltage measurements in a single transfer, allowing instantaneous power
> measurements.
> 
> Reads into the buffer can be triggered by any software triggers, e.g.
> the iio-trig-hrtimer:
> 
>     $ mkdir /sys/kernel/config/iio/triggers/hrtimer/my-trigger
>     $ cat /sys/bus/iio/devices/iio\:device3/name
>     lmp92064
>     $ iio_readdev -t my-trigger -b 16 iio:device3 | hexdump
>     WARNING: High-speed mode not enabled
>     0000000 0000 0176 0101 0001 5507 abd5 7645 1768
>     0000010 0000 016d 0101 0001 ee1e ac6b 7645 1768
>     ...
> 
> Signed-off-by: Leonard Göhrs <l.goehrs@...gutronix.de>
> ---
>  drivers/iio/adc/ti-lmp92064.c | 54 +++++++++++++++++++++++++++++++++++
>  1 file changed, 54 insertions(+)
> 
> diff --git a/drivers/iio/adc/ti-lmp92064.c b/drivers/iio/adc/ti-lmp92064.c
> index c30ed824924f3..03765c4057dda 100644
> --- a/drivers/iio/adc/ti-lmp92064.c
> +++ b/drivers/iio/adc/ti-lmp92064.c
> @@ -16,7 +16,10 @@
>  #include <linux/spi/spi.h>
>  
>  #include <linux/iio/iio.h>
> +#include <linux/iio/buffer.h>
>  #include <linux/iio/driver.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/iio/trigger_consumer.h>
>  
>  #define TI_LMP92064_REG_CONFIG_A 0x0000
>  #define TI_LMP92064_REG_CONFIG_B 0x0001
> @@ -91,6 +94,13 @@ static const struct iio_chan_spec lmp92064_adc_channels[] = {
>  		.address = TI_LMP92064_CHAN_INC,
>  		.info_mask_separate =
>  			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +		.scan_index = 0,
> +		.scan_type = {
> +			.sign = 'u',
> +			.realbits = 12,
> +			.storagebits = 16,
> +			.shift = 0,

As zero is the 'obvious' default for shift (do nothing case) and c will set it to 0 for
you anyway, no need to set it explicitly like this.

> +		},
>  		.datasheet_name = "INC",
>  	},
>  	{
> @@ -98,8 +108,16 @@ static const struct iio_chan_spec lmp92064_adc_channels[] = {
>  		.address = TI_LMP92064_CHAN_INV,
>  		.info_mask_separate =
>  			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +		.scan_index = 1,
> +		.scan_type = {
> +			.sign = 'u',
> +			.realbits = 12,
> +			.storagebits = 16,
> +			.shift = 0,

Same here. No need for this last line.

> +		},
>  		.datasheet_name = "INV",
>  	},
> +	IIO_CHAN_SOFT_TIMESTAMP(2),
>  };
>  
>  static int lmp92064_read_meas(struct lmp92064_adc_priv *priv, u16 *res)
> @@ -171,6 +189,37 @@ static int lmp92064_read_raw(struct iio_dev *indio_dev,
>  	}
>  }
>  
> +static irqreturn_t lmp92064_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct lmp92064_adc_priv *priv = iio_priv(indio_dev);
> +	int i = 0, j, ret;
> +	u16 raw[2];
> +	u16 *data;
> +
> +	ret = lmp92064_read_meas(priv, raw);
> +	if (ret < 0)
> +		goto done;
> +
> +	data = kmalloc(indio_dev->scan_bytes, GFP_KERNEL);

A driver shouldn't be directly accessing scan_bytes.
You will see iio.h that it is marked [INTERN] to show it should only be accessed
by the IIO core code.

The reasoning is closely related to Lars' point. This is almost always a small
structure with a known maximum size (across all possible channel configurations)
so allocate that space once not every scan (will be 16 bytes I think)


> +	if (!data)
> +		goto done;
> +
> +	for_each_set_bit(j, indio_dev->active_scan_mask, indio_dev->masklength)
> +		data[i++] = raw[j];
When a sensor 'always' reads the two channels, we can leave the necessary data
mangling up to the IIO core.

Provide available_scan_masks and then always push the lot every time.
Mostly people will want both channels anyway (as they paid for them ;)
so that core code that moves the data around will do nothing.  In the cases
where they only want one channel it will handle the complexity for you.

> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, data,
> +					   iio_get_time_ns(indio_dev));
> +
> +	kfree(data);
> +
> +done:
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
>  static int lmp92064_reset(struct lmp92064_adc_priv *priv,
>  			  struct gpio_desc *gpio_reset)
>  {
> @@ -302,6 +351,11 @@ static int lmp92064_adc_probe(struct spi_device *spi)
>  	indio_dev->num_channels = ARRAY_SIZE(lmp92064_adc_channels);
>  	indio_dev->info = &lmp92064_adc_info;
>  
> +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> +					      lmp92064_trigger_handler, NULL);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to setup buffered read\n");
> +
>  	return devm_iio_device_register(dev, indio_dev);
>  }
>  
> 
> base-commit: 9561de3a55bed6bdd44a12820ba81ec416e705a7