linux-kernel - Re: [PATCH 1/3] iio: adc: ad7768-1: fix one-shot mode data acquisition

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Message-ID: <20260207164851.51874c46@jic23-huawei>
Date: Sat, 7 Feb 2026 16:48:51 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Jonathan Santos <Jonathan.Santos@...log.com>
Cc: <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <Michael.Hennerich@...log.com>, <lars@...afoo.de>, <dlechner@...libre.com>,
 <nuno.sa@...log.com>, <andy@...nel.org>
Subject: Re: [PATCH 1/3] iio: adc: ad7768-1: fix one-shot mode data
 acquisition

On Sat, 31 Jan 2026 22:35:20 -0300
Jonathan Santos <Jonathan.Santos@...log.com> wrote:

> According to the datasheet, one-shot mode requires a SYNC_IN pulse to
> trigger a new sample conversion. In the current implementation, No sync
> pulse was sent after switching to one-shot mode and reinit_completion()
> was called before mode switching, creating a race condition where spurious
> interrupts during mode change could trigger completion prematurely.
> 
> Fix by sending a sync pulse after configuring one-shot mode and moving
> reinit_completion() after the pulse to ensure it only waits for the
> actual conversion completion.
That smells like a race...

What stops us taking a long break between ending that sync pulse and
the reinit_completition() such that we have initialized if before the
complete()?

You always have to do it before what ever ultimately makes the complete()
happen. Have you seen an sign of the spurious interrupts or is that
more a conjecture of what might happen? 

Jonathan

> 
> Fixes: a5f8c7da3dbe ("iio: adc: Add AD7768-1 ADC basic support")
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> ---
>  drivers/iio/adc/ad7768-1.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> index fcd8aea7152e..8d39b71703ae 100644
> --- a/drivers/iio/adc/ad7768-1.c
> +++ b/drivers/iio/adc/ad7768-1.c
> @@ -463,12 +463,17 @@ static int ad7768_scan_direct(struct iio_dev *indio_dev)
>  	struct ad7768_state *st = iio_priv(indio_dev);
>  	int readval, ret;
>  
> -	reinit_completion(&st->completion);
> -
>  	ret = ad7768_set_mode(st, AD7768_ONE_SHOT);
>  	if (ret < 0)
>  		return ret;
>  
> +	/* One-shot mode requires a SYNC pulse to generate a new sample */
> +	ret = ad7768_send_sync_pulse(st);
> +	if (ret)
> +		return ret;
> +
> +	reinit_completion(&st->completion);
> +
>  	ret = wait_for_completion_timeout(&st->completion,
>  					  msecs_to_jiffies(1000));
>  	if (!ret)