linux-kernel - Re: [PATCH v2] iio: adc: ad7173: prevent scan if too many setups requested

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Message-ID: <aIDzAiQT0S0-ZcQo@smile.fi.intel.com>
Date: Wed, 23 Jul 2025 17:34:42 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: David Lechner <dlechner@...libre.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iio: adc: ad7173: prevent scan if too many setups
 requested

On Tue, Jul 22, 2025 at 02:20:07PM -0500, David Lechner wrote:
> Add a check to ad7173_update_scan_mode() to ensure that we didn't exceed
> the maximum number of unique channel configurations.
> 
> In the AD7173 family of chips, there are some chips that have 16
> CHANNELx registers but only 8 setups (combination of CONFIGx, FILTERx,
> GAINx and OFFSETx registers). Since commit 92c247216918 ("iio: adc:
> ad7173: fix num_slots"), it is possible to have more than 8 channels
> enabled in a scan at the same time, so it is possible to get a bad
> configuration when more than 8 channels are using unique configurations.
> This happens because the algorithm to allocate the setup slots only
> takes into account which slot has been least recently used and doesn't
> know about the maximum number of slots available.
> 
> Since the algorithm to allocate the setup slots is quite complex, it is
> simpler to check after the fact if the current state is valid or not.
> So this patch adds a check in ad7173_update_scan_mode() after setting up
> all of the configurations to make sure that the actual setup still
> matches the requested setup for each enabled channel. If not, we prevent
> the scan from being enabled and return an error.
> 
> The setup comparison in ad7173_setup_equal() is refactored to a separate
> function since we need to call it in two places now.

...

> + * ad7173_setup_equal - Compare two channel setups

Better naming is
ad7173_is_setup_equal().

-- 
With Best Regards,
Andy Shevchenko