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

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Message-ID: <20250718221850.614d05b3@pumpkin>
Date: Fri, 18 Jul 2025 22:18:50 +0100
From: David Laight <david.laight.linux@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: David Lechner <dlechner@...libre.com>, 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 Sun, 13 Jul 2025 15:04:45 +0100
Jonathan Cameron <jic23@...nel.org> wrote:

> 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.

Maybe not - it looks like there is a read on one place and write in another.
Both are passed the same address.
The interface looks very strange though.

But the updated code is writing uninitialised stack.

	David
 
> > ---
> >  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,  
> 
>