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Date: Sun, 24 Mar 2024 12:45:46 +0000
From: Jonathan Cameron <jic23@kernel.org>
To: David Lechner <dlechner@baylibre.com>
Cc: Marcelo Schmitt <marcelo.schmitt@analog.com>, lars@metafoo.de,
 Michael.Hennerich@analog.com, robh+dt@kernel.org,
 krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
 marcelo.schmitt1@gmail.com, linux-iio@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] iio: adc: Add support for AD4000
Message-ID: <20240324124546.2e07f802@jic23-huawei>
In-Reply-To: <CAMknhBH7umcBD0hyt=6fOKu9E8k=CSrnNE4Z+9ynn0F4B=Wk2w@mail.gmail.com>
References: <cover.1711131830.git.marcelo.schmitt@analog.com>
	<15a70e55d7b6f0a97c4042bdaa41c2b672eb4f2f.1711131830.git.marcelo.schmitt@analog.com>
	<CAMknhBH7umcBD0hyt=6fOKu9E8k=CSrnNE4Z+9ynn0F4B=Wk2w@mail.gmail.com>
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On Sat, 23 Mar 2024 16:53:17 -0500

> > +
> > +       /*
> > +        * DMA (thus cache coherency maintenance) requires the
> > +        * transfer buffers to live in their own cache lines.
> > +        */
> > +       union {
> > +               struct {
> > +                       u8 sample_buf[4];
> > +                       s64 timestamp;  
> 
> Usually we see __aligned(8) applied to the timestamp (I'm guessing
> some archs need it?)
> 
Good spot. Yes, x86_32 is the one that we most commonly refer to for this.
It aligns s64 to only 32 bits whereas IIO ABI is always naturally aligned.

> > +               } scan;
> > +               u8 d8[2];
> > +       } data __aligned(IIO_DMA_MINALIGN);
> > +};