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

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Message-ID: <1efe9234-a97f-6df2-c47d-e153dc362599@roeck-us.net>
Date:   Wed, 30 Aug 2023 12:32:14 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Naresh Solanki <naresh.solanki@...ements.com>
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

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 ?

Thanks,
Guenter