linux-kernel - Re: [PATCH v2 1/3] kernel: Provide a _

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Date:   Tue, 7 May 2019 16:21:02 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        Jean Delvare <jdelvare@...e.com>,
        linux-arm-kernel@...ts.infradead.org,
        "open list:HARDWARE MONITORING" <linux-hwmon@...r.kernel.org>,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2 1/3] kernel: Provide a __pow10() function

On 5/7/19 2:49 PM, Florian Fainelli wrote:
> On 5/7/19 2:06 PM, Guenter Roeck wrote:
>> On Tue, May 07, 2019 at 12:35:02PM -0700, Florian Fainelli wrote:
>>> Provide a simple macro that can return the value of 10 raised to a
>>> positive integer. We are going to use this in order to scale units from
>>> firmware to HWMON.
>>>
>>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>>> ---
>>>   include/linux/kernel.h | 11 +++++++++++
>>>   1 file changed, 11 insertions(+)
>>>
>>> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
>>> index 2d14e21c16c0..62fc8bd84bc9 100644
>>> --- a/include/linux/kernel.h
>>> +++ b/include/linux/kernel.h
>>> @@ -294,6 +294,17 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro)
>>>   	return (u32)(((u64) val * ep_ro) >> 32);
>>>   }
>>>   
>>> +/* Return in f the value of 10 raise to the power x */
>>> +#define __pow10(x, f)(					\
>>> +{							\
>>> +	typeof(x) __x = abs(x);				\
>>> +	f = 1;						\
>>> +	while (__x--)					\
>>> +		f *= 10;				\
>>> +	f;						\
>>> +}							\
>>> +)
>>
>> Kind of unusual. I would have expected to use this like
>> 	f = __pow10(x);
>> ie without having to provide f as parameter. That would be much less
>> confusing. I assume this is to make the result type independent, but
>> I am not sure if that is worth the trouble.
> 
> Correct, that was the intent here.
> 
>>
>> Are there users outside the hwmon code ? If not, it might be simpler
>> to keep it there for now.
> 
> There appears to be a few outside actually:
> 
> drivers/acpi/sbs.c::battery_scale
> drivers/iio/common/hid-sensors/hid-sensor-attributes.c::pow_10
> 
> There could be others but those two came out as obvious candidates.
> 
> Would you be okay with a local pow10 function within scmi-hwmon.c and a
> subsequent patch series providing a common function?
> 

I would prefer that, actually, to reduce dependencies.

Thanks,
Guenter