linux-kernel - Re: [PATCH v2] iio: adc: add buffering support to the TI LMP92064 ADC driver

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Date:   Sun, 2 Jul 2023 18:09:03 +0800
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Leonard Göhrs <l.goehrs@...gutronix.de>
CC:     <kernel@...gutronix.de>, Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] iio: adc: add buffering support to the TI LMP92064
 ADC driver

On Thu, 22 Jun 2023 08:53:41 +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>

A minor follow up comment inline.

>  static int lmp92064_read_meas(struct lmp92064_adc_priv *priv, u16 *res)
> @@ -171,6 +192,29 @@ 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;
> +	} data;
> +	int ret;
> +
> +	ret = lmp92064_read_meas(priv, data.values);
> +	if (ret >= 0) {
Even thought it's more code, in IIO at least we tend to prefer to handle
errors out of line

	if (ret) 
		goto err;
	
	iio_push_to_buffers....


err:
	iio_trigger_notify_done()

	return IRQ_HANDLED;

Also, read_meas doesn't return > 0 which is implied by the above check.

> +		/* Only push values if the read succeeded */
> +		iio_push_to_buffers_with_timestamp(indio_dev, &data,
> +						   iio_get_time_ns(indio_dev));
> +	}
> +
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +