linux-kernel - Re: [PATCH v2] iio: adc: ad7606_spi: add offload scan mask check

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Message-ID: <20250504153756.27cf44fb@jic23-huawei>
Date: Sun, 4 May 2025 15:37:56 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Andy Shevchenko <andy.shevchenko@...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>, Angelo Dureghello
 <adureghello@...libre.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iio: adc: ad7606_spi: add offload scan mask check

On Fri, 2 May 2025 21:21:49 +0300
Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Fri, May 2, 2025 at 6:42 PM David Lechner <dlechner@...libre.com> wrote:
> >
> > Validate the scan mask when SPI offloading is being used.
> >
> > Since this family of ADCs is simultaneous sampling, there isn't a way
> > to selectively disable channels when reading sample data. (Technically,
> > AD7616 has a sequencer so could have some control, but that is for  
> 
> so it could
tweaked to 
so the driver could
given 'it' would otherwise refer to the chip rather than the software.

Good catch.

Applied.

> 
> > another day).
> >
> > For "regular" IIO triggered buffer reads, this isn't a problem and the
> > IIO core will demux the data and ignore data from disabled channels.
> > However, since SPI offloading is done completely in hardware, we don't
> > have a way to do the same. So before this patch, if less than all
> > channels were enabled, the data would be misplaced in the buffer.
> >
> > By adding a check in update_scan_mode, we can fail to enable the buffer
> > instead of having bad data returned to userspace.  
> 
> Reviewed-by: Andy Shevchenko <andy@...nel.org>
>