linux-kernel - Re: [PATCH] iio:proximity:sx9324: Fix hardware gain read/write

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Message-ID: <CAHp75Ve+SiiAM6VkiwPt95w68KEDk46vXR6ZzjOR7ZgaeZ80HA@mail.gmail.com>
Date:   Mon, 28 Mar 2022 01:16:10 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Gwendal Grignou <gwendal@...omium.org>
Subject: Re: [PATCH] iio:proximity:sx9324: Fix hardware gain read/write

On Sat, Mar 19, 2022 at 5:58 AM Stephen Boyd <swboyd@...omium.org> wrote:
>
> There are four possible gain values according to sx9324_gain_vals[]: 1,
> 2, 4, and 8. When writing and reading the register the values are off by
> one. The bits should be set according to this equation:
>
>         ilog2(<gain>) + 1
>
> so that a gain of 8 is 0x3 in the register field and a gain of 4 is 0x2
> in the register field, etc. Fix up the functions.

...

> +       *val = 1 << regval;

I see it's similar in the original code, but this is still problematic
from C standard point of view, i.e. if regval = 31, the C standard
calls it UB (Undefined Behaviour).

-- 
With Best Regards,
Andy Shevchenko