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

[Andy Shevchenko]

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