On Fri, Jun 25, 2021 at 6:39 PM Pali Rohár [off-list ref] wrote:

On Friday 25 June 2021 17:22:31 Geert Uytterhoeven wrote:

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On Fri, Jun 25, 2021 at 4:37 PM Pali Rohár [off-list ref] wrote:

...

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+/*
+ * DIV_U64_ROUND_CLOSEST - unsigned 64bit divide with 32bit divisor rounded to nearest integer

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+ * @dividend: unsigned 64bit dividend

(1)

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+ * @divisor: unsigned 32bit divisor
+ *
+ * Divide unsigned 64bit dividend by unsigned 32bit divisor
+ * and round to closest integer.
+ *
+ * Return: dividend / divisor rounded to nearest integer
+ */
+#define DIV_U64_ROUND_CLOSEST(dividend, divisor)       \
+       ({ u32 _tmp = (divisor); div_u64((u64)(dividend) + _tmp / 2, _tmp); })

Given "dividend" should already be an unsigned 64-bit value, I don't
think the cast to "u64" is needed. Similar macros in this file also
don't have the cast.

It is just to ensure that plus operation between dividend and _tmp is
evaluated in 64-bit context to prevent overflow. Just a case when user
calls this macro with 32-bit dividend param.

This contradicts (1).

As it is a macro (and not
inline function) type is not automatically enforced.

DIV_S64_ROUND_CLOSEST macro assigns its argument into temporary 64-bit
variable which then ensures usage of 64-bit arithmetic operations. Same
applies for DIV64_U64_ROUND_CLOSEST and DIV64_U64_ROUND_UP macros.

So this is reason why I added explicit cast to u64.

I don't see the reason for casting in the current code. Probably you
need to rephrase documentation to explain why it's there.

-- 
With Best Regards,
Andy Shevchenko