linux-kernel - Re: [PATCH] iio: adc: ad7606: explicit timestamp alignment

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Message-ID: <20250504155544.60fe3464@jic23-huawei>
Date: Sun, 4 May 2025 15:55:44 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>
Cc: David Lechner <dlechner@...libre.com>, Michael Hennerich 
 <Michael.Hennerich@...log.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: adc: ad7606: explicit timestamp alignment

On Tue, 29 Apr 2025 14:01:54 +0100
Nuno Sá <noname.nuno@...il.com> wrote:

> On Mon, 2025-04-28 at 21:17 -0500, David Lechner wrote:
> > Use struct with aligned_s64 timestamp to make timestamp alignment
> > explicit. Technically, what we have works because for all known
> > architectures, IIO_DMA_MINALIGN is a multiple of __alignof__(s64).
> > But this way, we don't have to make people read the comments to know
> > why there are extra elements in each buffer.
> > 
> > ---  
> 
> Reviewed-by: Nuno Sá <nuno.sa@...log.com>
Applied to the togreg branch of iio.git and pushed out as testing
for all the normal reasons.

Thanks,

Jonathan

> 
> >  drivers/iio/adc/ad7606.h | 13 ++++++++-----
> >  1 file changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/ad7606.h b/drivers/iio/adc/ad7606.h
> > index
> > 89d49551eaf515bab9706c12bff056dfcb707b67..441e62c521bcbea69b4f70bb2d55f65334d2
> > 2276 100644
> > --- a/drivers/iio/adc/ad7606.h
> > +++ b/drivers/iio/adc/ad7606.h
> > @@ -155,12 +155,15 @@ struct ad7606_state {
> >  	/*
> >  	 * DMA (thus cache coherency maintenance) may require the
> >  	 * transfer buffers to live in their own cache lines.
> > -	 * 16 * 16-bit samples + 64-bit timestamp - for AD7616
> > -	 * 8 * 32-bit samples + 64-bit timestamp - for AD7616C-18 (and
> > similar)
> > +	 * 16 * 16-bit samples for AD7616
> > +	 * 8 * 32-bit samples for AD7616C-18 (and similar)
> >  	 */
> > -	union {
> > -		u16 buf16[20];
> > -		u32 buf32[10];
> > +	struct {
> > +		union {
> > +			u16 buf16[16];
> > +			u32 buf32[8];
> > +		};
> > +		aligned_s64 timestamp;
> >  	} data __aligned(IIO_DMA_MINALIGN);
> >  	__be16				d16[2];
> >  };
> > 
> > ---
> > base-commit: b475195fecc79a1a6e7fb0846aaaab0a1a4cb2e6
> > change-id: 20250428-iio-adc-ad7606-fix-buffer-alignment-9fcde71687dc
> > 
> > Best regards,