Re: [PATCH] iwlwifi: mvm: Use div64_s64 instead of do_div in iwl_mvm_debug_range_resp

Luca Coelho
2019-02-20T09:40:03Z

On Tue, 2019-02-19 at 11:05 -0800, Nick Desaulniers wrote:
> On Tue, Feb 19, 2019 at 10:21 AM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> > Clang warns:
> >
> > drivers/net/wireless/intel/iwlwifi/mvm/ftm-initiator.c:465:2:
> > warning:
> > comparison of distinct pointer types ('typeof ((rtt_avg)) *' (aka
> > 'long
> > long *') and 'uint64_t *' (aka 'unsigned long long *'))
> > [-Wcompare-distinct-pointer-types]
> > do_div(rtt_avg, 6666);
> > ^~~~~~~~~~~~~~~~~~~~~
> > include/asm-generic/div64.h:222:28: note: expanded from macro
> > 'do_div'
> > (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
> > ~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~
> > 1 warning generated.
> >
> > do_div expects an unsigned dividend. Use div64_s64, which expects a
> > signed dividend.
>
> Eh, IIRC, signed vs unsigned division has implications for rounding
> towards zero or not, but I doubt that the round trip time average
> (RTT
> avg) should ever be negative. General rule of thumb for C is to keep
> arithmetic signed (even when working with non zero values), so rather
> than make the literal (6666) a unsigned long, I agree with your
> change
> to keep the division signed as well. Thanks for the fix.
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Thanks for the patch and for the review. I've applied this to our
internal tree and it will be sent upstreaming following our normal
upstreaming process.

--
Cheers,
Luca.