linux-kernel - Re: [PATCH] iio: proximity: isl29501: use scan struct instead of array

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Message-ID: <20250713150445.3965931c@jic23-huawei>
Date: Sun, 13 Jul 2025 15:04:45 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Nuno Sá <nuno.sa@...log.com>, Andy Shevchenko
 <andy@...nel.org>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: proximity: isl29501: use scan struct instead of
 array

On Fri, 11 Jul 2025 11:18:13 -0500
David Lechner <dlechner@...libre.com> wrote:

> Replace the scan buffer array with a struct that contains a single u32
> for the data and an aligned_s64 for the timestamp. This makes it easier
> to see the intended layout of the buffer and avoids the need to manually
> calculate the number of extra elements needed for an aligned timestamp.
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
Why are we using a u32 here?  It's a 16 bit
read in that isl29501_register_read() call
and storagebits = 16 in the chan spec.

So to me looks like you found a bug for big endian platforms.
> ---
>  drivers/iio/proximity/isl29501.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/proximity/isl29501.c b/drivers/iio/proximity/isl29501.c
> index d1510fe2405088adc0998e28aa9f36e0186fafae..0eed14f66ab700473af10414b25a56458335b381 100644
> --- a/drivers/iio/proximity/isl29501.c
> +++ b/drivers/iio/proximity/isl29501.c
> @@ -938,12 +938,15 @@ static irqreturn_t isl29501_trigger_handler(int irq, void *p)
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	struct isl29501_private *isl29501 = iio_priv(indio_dev);
>  	const unsigned long *active_mask = indio_dev->active_scan_mask;
> -	u32 buffer[4] __aligned(8) = {}; /* 1x16-bit + naturally aligned ts */
> +	struct {
> +		u32 data;
> +		aligned_s64 ts;
> +	} scan;
>  
>  	if (test_bit(ISL29501_DISTANCE_SCAN_INDEX, active_mask))
> -		isl29501_register_read(isl29501, REG_DISTANCE, buffer);
> +		isl29501_register_read(isl29501, REG_DISTANCE, &scan.data);
>  
> -	iio_push_to_buffers_with_timestamp(indio_dev, buffer, pf->timestamp);
> +	iio_push_to_buffers_with_timestamp(indio_dev, &scan, pf->timestamp);
>  	iio_trigger_notify_done(indio_dev->trig);
>  
>  	return IRQ_HANDLED;
> 
> ---
> base-commit: f8f559752d573a051a984adda8d2d1464f92f954
> change-id: 20250711-iio-use-more-iio_declare_buffer_with_ts-7-880ddf1d3070
> 
> Best regards,