linux-kernel - Re: [PATCH v2] iio: adc: ad7124: change setup reg allocation strategy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aP9ifk-ms8RJi5ff@smile.fi.intel.com>
Date: Mon, 27 Oct 2025 14:15:58 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: David Lechner <dlechner@...libre.com>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iio: adc: ad7124: change setup reg allocation strategy

On Tue, Sep 23, 2025 at 04:48:04PM -0500, David Lechner wrote:
> Change the allocation strategy of the 8 SETUP registers from a least-
> recently-used (LRU) to a first-come-first-served basis.
> 
> The AD7124 chips can have up to 16 channels enabled at a time in the
> sequencer for buffered reads, but only have 8 SETUP configurations
> (namely the OFFSET, GAIN, CONFIG and FILTER registers) that must be
> shared among the 16 channels.  This means some of the channels must use
> the exact same configuration parameters so that they can share a single
> SETUP group of registers.  The previous LRU strategy did not keep track
> of how many different configurations were requested at the same time,
> so if there were more than 8 different configurations requested, some
> channels would end up using the incorrect configuration because the slot
> assigned to them would also be assigned to a different configuration
> that wrote over it later.
> 
> Adding such tracking to solve this would make an already complex
> algorithm even more complex.  Instead we can replace it with a simpler
> first-come-first-serve strategy.  This makes it easy to track how many
> different configurations are being requested at the same time.  This
> comes at the expense of slightly longer setup times for buffered reads
> since all setup registers must be written each time when a buffered read
> is enabled.  But this is generally not considered a hot path where
> performance is critical, so should be acceptable.
> 
> This new strategy also makes hardware debugging easier since SETUPs are
> now assigned in a deterministic manner and in a logical order.

...

> +#define AD7124_CFG_SLOT_UNASSIGNED	~0U

Perhaps one of Uxx_MAX should be used instead?

-- 
With Best Regards,
Andy Shevchenko