linux-kernel - Re: [PATCH] regulator (max5970): Add hwmon support

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Message-ID: <CABqG17hhPUjSKoAxVFKAmrZfQ0TpTRWVpoe-CrRAu0i7jt=JFw@mail.gmail.com>
Date:   Thu, 31 Aug 2023 14:26:48 +0530
From:   Naresh Solanki <naresh.solanki@...ements.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jean Delvare <jdelvare@...e.com>, zev@...ilderbeest.net,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org
Subject: Re: [PATCH] regulator (max5970): Add hwmon support

Hi


On Thu, 31 Aug 2023 at 01:02, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 8/30/23 12:14, Naresh Solanki wrote:
> > Hi
> >
> [ ... ]
> >>> +                     /*
> >>> +                      * Calculate voltage from ADC value and MON range.
> >>> +                      * ddata->mon_rng holds the voltage corresponding to the maximum value the
> >>> +                      * 10-bit ADC can measure.
> >>> +                      * To obtain the output, multiply the ADC value by the MON range (in
> >>> +                      * microvolts) and then divide it by the maximum value of the 10-bit ADC.
> >>> +                      */
> >>> +                     *val = mul_u64_u32_shr(*val, ddata->mon_rng[channel], 10);
> >>
> >> Why do you use mul_u64_u32_shr() here but a direct shift above ?
> > There is possibility of overflow due to large value of ddata->mon_rng
>
> Does the right shift guarantee that the result fits into 32 bit ?
Yes. Value in ddata->mon_rng can go upto 26bits, & ADC is 10 bit.
The 10 bit right shift(part of calculation) makes sure the result
never exceed 32 bit

Regards,
Naresh
>
> Thanks,
> Guenter
>