linux-kernel - Re: [PATCH 2/6] iio: adc: ad7606: fix issue/quirk with find

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Message-ID: <CA+GgBR-8i-S2gnp39TnOxayfGqLpdhAceOjNDpE+Y7t_5Xeaig@mail.gmail.com>
Date: Tue, 22 Oct 2024 09:31:38 +0300
From: Alexandru Ardelean <aardelean@...libre.com>
To: David Lechner <dlechner@...libre.com>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, jic23@...nel.org, krzk+dt@...nel.org, 
	robh@...nel.org, lars@...afoo.de, michael.hennerich@...log.com, 
	gstols@...libre.com, brgl@...ev.pl
Subject: Re: [PATCH 2/6] iio: adc: ad7606: fix issue/quirk with find_closest()
 for oversampling

On Mon, Oct 21, 2024 at 10:31 PM David Lechner <dlechner@...libre.com> wrote:
>
> On 10/21/24 2:03 PM, David Lechner wrote:
> > On 10/21/24 8:02 AM, Alexandru Ardelean wrote:
> >> There's a small issue with setting oversampling-ratio that seems to have
> >> been there since the driver was in staging.
> >> Trying to set an oversampling value of '2' will set an oversampling value
> >> of '1'. This is because find_closest() does an average + rounding of 1 + 2,
> >> and we get '1'.
> >>
> >> This is the only issue with find_closest(), at least in this setup. The
> >> other values (above 2) work reasonably well. Setting 3, rounds to 2, so a
> >> quick fix is to round 'val' to 3 (if userspace provides 2).
> >
> > This sounds like a bug in find_closest() instead of in this driver.
> >

Adding Bart (the original author of find_closest()).

> > If there is an exact match in the list, it seems reasonable to expect
> > that the exact match is returned by find_closest().
> >
>
> Likely also affected by this bug since they have values 1, 2 in the list:
>
> * rtq6056_adc_set_average()
> * si1133_scale_to_swgain()

Yeah.
I forgot to mention this sooner.
But this patch is more of an RFC patch about how to handle this
situation with find_closest().

For monotonic values with an increment of 1, find_closest() is a bit buggy.
Will try to fix find_closest()

>