[S] Change in coreboot[main]: arch/arm64/arch_timer: Fix possible overflow in multiplication

[Julius Werner (Code Review)]

Attention is currently required from: Paul Menzel, Yidi Lin, Yu-Ping Wu.

Julius Werner has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/78800?usp=email )

Change subject: arch/arm64/arch_timer: Fix possible overflow in multiplication
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Patch Set 2:

(3 comments)

File src/arch/arm64/arch_timer.c:

https://review.coreboot.org/c/coreboot/+/78800/comment/eea52878_ae8cb645 :
PS2, Line 16: 		assert(tfreq > 0)
Missing semicolon (also, this is probably not necessary, you'll get a pretty obvious division-by-zero exception when this is not initialized anyway).

https://review.coreboot.org/c/coreboot/+/78800/comment/088f888b_eaa045be :
PS2, Line 18: 		div = gcd(mult, tfreq);
nit: depending on the GCD implementation you'll probably want to write it as `gcd(tfreq, mult)` to help it terminate a little faster (in the common case where tfreq is a multiple of mult).

https://review.coreboot.org/c/coreboot/+/78800/comment/107e6c51_75e29c0f :
PS2, Line 11: static uint32_t tfreq, mult;
            : 	uint32_t div;
            : 
            : 	if (tfreq == 0) {
            : 		tfreq = raw_read_cntfrq_el0();
            : 		assert(tfreq > 0)
            : 		mult = 1000000;
            : 		div = gcd(mult, tfreq);
            : 		tfreq /= div;
            : 		mult /= div;
            : 	}
            : 
            : 	long usecs = (tvalue * mult) / tfreq;
> Nice, but why not just cast `tvalue`, and let the compiler figure out the rest? Is that possible?

Not really sure what you want to cast it to? It's already 64-bit. The concern here is that even the 64-bit multiplication could overflow since the initialization value of CNTPCT is unknown.