netdev - Re: [PATCH] iwlwifi: mvm: Use div64_s64 instead of do_div in iwl_mvm_debug_range

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Message-ID: <cd93696bcca66944ec2d472758d86e8f7c6e81de.camel@coelho.fi>
Date:   Wed, 20 Feb 2019 11:39:54 +0200
From:   Luca Coelho <luca@...lho.fi>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>
Cc:     Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Intel Linux Wireless <linuxwifi@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iwlwifi: mvm: Use div64_s64 instead of do_div in
 iwl_mvm_debug_range_resp

On Tue, 2019-02-19 at 11:05 -0800, Nick Desaulniers wrote:
> On Tue, Feb 19, 2019 at 10:21 AM Nathan Chancellor
> <natechancellor@...il.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@...gle.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.