linux-kernel - Re: [PATCH v2 01/11] iio: adc: ad_sigma_delta: don't overallocate scan buffer

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Message-ID: <20250628160402.1f97c0fe@jic23-huawei>
Date: Sat, 28 Jun 2025 16:04:02 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Mark Brown <broonie@...nel.org>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH v2 01/11] iio: adc: ad_sigma_delta: don't overallocate
 scan buffer

On Sat, 28 Jun 2025 15:55:21 +0100
Jonathan Cameron <jic23@...nel.org> wrote:

> On Fri, 27 Jun 2025 18:39:57 -0500
> David Lechner <dlechner@...libre.com> wrote:
> 
> > Fix overallocating the size of the scan buffer by converting bits to
> > bytes. The size is meant to be in bytes, so scanbits needs to be
> > divided by 8.
> > 
> > Signed-off-by: David Lechner <dlechner@...libre.com>
> > ---
> >  drivers/iio/adc/ad_sigma_delta.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
> > index 4c5f8d29a559fea7226b84141bcb148fb801f62c..6b3ef7ef403e00804abeb81025ed293b188e492b 100644
> > --- a/drivers/iio/adc/ad_sigma_delta.c
> > +++ b/drivers/iio/adc/ad_sigma_delta.c
> > @@ -489,7 +489,7 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
> >  			return ret;
> >  	}
> >  
> > -	samples_buf_size = ALIGN(slot * indio_dev->channels[0].scan_type.storagebits, 8);
> > +	samples_buf_size = ALIGN(slot * indio_dev->channels[0].scan_type.storagebits / 8, 8);  
> 
> Seems like a good place for BITS_TO_BYTES() from bitops.h.  Given we have another 8
> kicking around in the same code line it might be a tiny bit confusing as / 8
> 
> If everything else is good I'll tweak this whilst applying (and add the include if needed).

Found it in patch 4.   No problem doing it there.  'Maybe' a hint in the description would
have been a nice to have, but not particularly important.

> 
> >  	samples_buf_size += sizeof(int64_t);
> >  	samples_buf = devm_krealloc(&sigma_delta->spi->dev, sigma_delta->samples_buf,
> >  				    samples_buf_size, GFP_KERNEL);
> >   
>