linux-kernel - Re: [PATCH] iio: adc: ad4000: Avoid potential double data word read

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Message-ID: <CAHp75VendQGLdpggySS3mX6M2YSeS70bvE8yg7sp_LNGDS-Scg@mail.gmail.com>
Date: Tue, 15 Apr 2025 21:02:47 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Marcelo Schmitt <marcelo.schmitt@...log.com>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, jic23@...nel.org, 
	lars@...afoo.de, Michael.Hennerich@...log.com, nuno.sa@...log.com, 
	andy@...nel.org, marcelo.schmitt1@...il.com, 
	David Lechner <dlechner@...libre.com>
Subject: Re: [PATCH] iio: adc: ad4000: Avoid potential double data word read

On Tue, Apr 15, 2025 at 3:21 PM Marcelo Schmitt
<marcelo.schmitt@...log.com> wrote:
>
> Currently, SPI-Engine offload module always sends 32-bit data elements to
> DMA engine. Appropriately, when set for SPI offloading, the IIO driver uses
> 32 storagebits for IIO ADC channel buffer elements. However, setting SPI
> transfer length according to storagebits (32-bits in case of offload) can
> lead to unnecessarily long transfers for ADCs that are 16-bit or less
> precision. Adjust AD4000 single-shot read to run transfers of 2 bytes when
> that is enough to get all ADC data bits.

...

>         xfers[1].rx_buf = &st->scan.data;
> -       xfers[1].len = BITS_TO_BYTES(chan->scan_type.storagebits);
> +       xfers[1].len = chan->scan_type.realbits > 16 ? 4 : 2;

But wouldn't be logical to have

       xfers[1].len = BITS_TO_BYTES(chan->scan_type.realbits);

?

-- 
With Best Regards,
Andy Shevchenko