Re: [PATCH v4] iio: adc: add buffering support to the TI LMP92064 ADC driver

[Jonathan Cameron]

On Fri,  7 Jul 2023 08:36:35 +0200
Leonard Göhrs <l.goehrs@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>

Applied, with a tweaked commit message (to put the driver name after the iio: adc:
as the driver already exists).

Applied to the togreg branch of iio.git but as we are mid merge window, I'll wait
until I can rebase on rc1. For now just pushed out as testing to see if 0-day
can find any issues that we missed.

Thanks,

Jonathan

> ---
> Changes v1->v2:
> 
>   - Remove superfluous .shift = 0 initialization in scan_type.
>   - Replace kmalloc buffer allocation for every read with a stack
>     allocated structure.
>     A struct is used to ensure correct alignment of the timestamp field.
>     See e.g. adc/rockchip_saradc.c for other users of the same pattern.
>   - Use available_scan_masks and always push both voltage and current
>     measurements to the buffer.
> 
> Changes v2->v3:
> 
>   - Handle errors returned by lmp92064_read_meas() out-of-line via
>     a goto err;
> 
> Changes v3->v4:
> 
>   - 8-Byte align the 64 bit timestamp in the buffer structure
>     and memset() the stack-allocated buffer to prevent leaking
>     kernel memory to userspace. (Thanks to Nuno Sá)
> ---
>  drivers/iio/adc/ti-lmp92064.c | 53 +++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/drivers/iio/adc/ti-lmp92064.c b/drivers/iio/adc/ti-lmp92064.c
> index c30ed824924f3..84ba5c4a0eea7 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 +94,12 @@ 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 = TI_LMP92064_CHAN_INC,
> +		.scan_type = {
> +			.sign = 'u',
> +			.realbits = 12,
> +			.storagebits = 16,
> +		},
>  		.datasheet_name = "INC",
>  	},
>  	{
> @@ -98,8 +107,20 @@ 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 = TI_LMP92064_CHAN_INV,
> +		.scan_type = {
> +			.sign = 'u',
> +			.realbits = 12,
> +			.storagebits = 16,
> +		},
>  		.datasheet_name = "INV",
>  	},
> +	IIO_CHAN_SOFT_TIMESTAMP(2),
> +};
> +
> +static const unsigned long lmp92064_scan_masks[] = {
> +	BIT(TI_LMP92064_CHAN_INC) | BIT(TI_LMP92064_CHAN_INV),
> +	0
>  };
>  
>  static int lmp92064_read_meas(struct lmp92064_adc_priv *priv, u16 *res)
> @@ -171,6 +192,32 @@ 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);
> +	struct {
> +		u16 values[2];
> +		int64_t timestamp __aligned(8);
> +	} data;
> +	int ret;
> +
> +	memset(&data, 0, sizeof(data));
> +
> +	ret = lmp92064_read_meas(priv, data.values);
> +	if (ret)
> +		goto err;
> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, &data,
> +					   iio_get_time_ns(indio_dev));
> +
> +err:
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
>  static int lmp92064_reset(struct lmp92064_adc_priv *priv,
>  			  struct gpio_desc *gpio_reset)
>  {
> @@ -301,6 +348,12 @@ static int lmp92064_adc_probe(struct spi_device *spi)
>  	indio_dev->channels = lmp92064_adc_channels;
>  	indio_dev->num_channels = ARRAY_SIZE(lmp92064_adc_channels);
>  	indio_dev->info = &lmp92064_adc_info;
> +	indio_dev->available_scan_masks = lmp92064_scan_masks;
> +
> +	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: 6995e2de6891c724bfeb2db33d7b87775f913ad1