linux-kernel - Re: [PATCH v2 2/6] units: Add 32- and 64-bit signed values of π

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Message-ID: <45bf8a0c-0491-4356-ad54-79c25079ad19@baylibre.com>
Date: Fri, 7 Nov 2025 15:14:04 -0600
From: David Lechner <dlechner@...libre.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Hans Verkuil <hverkuil+cisco@...nel.org>, linux-iio@...r.kernel.org,
 chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org
Cc: Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Benson Leung <bleung@...omium.org>, Guenter Roeck <groeck@...omium.org>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 "Daniel W. S. Almeida" <dwlsalmeida@...il.com>
Subject: Re: [PATCH v2 2/6] units: Add 32- and 64-bit signed values of π

On 11/7/25 3:09 PM, David Lechner wrote:
> On 11/7/25 2:03 PM, Andy Shevchenko wrote:
>> There are a few drivers that want to have these values, and
>> one more known to come soon. Let's define the values for them.
>>
>> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>> ---
>>  include/linux/units.h | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/include/linux/units.h b/include/linux/units.h
>> index f626e212d4ca..5b3293bce04c 100644
>> --- a/include/linux/units.h
>> +++ b/include/linux/units.h
>> @@ -21,6 +21,12 @@
>>  #define PICO	1000000000000ULL
>>  #define FEMTO	1000000000000000ULL
>>  
>> +/* Value of π * 10⁸ (fits s32 or signed int) */
>> +#define PI	314159265
> 
> It isn't clear to me at all in the other patches that e.g.
> DIV_ROUND_UP(PI, 1000) would be π ✕ 10⁴ (rounded to nearest

Typo. Should be DIV_ROUND_UP(PI, 10000) or  DIV_ROUND_UP(PI, 10 * KILO).

> integer, of course).
> 
> Calling these PI_E8 and PI_E18 or PI_x10_8 and PI_x10_18
> would help to clear that up.
> 
>> +
>> +/* Value of π * 10¹⁸ (fits s64 or signed long long) */
>> +#define PI_LL	3141592653589793238LL
>> +
>>  /* Hz based multipliers */
>>  #define NANOHZ_PER_HZ		1000000000UL
>>  #define MICROHZ_PER_HZ		1000000UL
>