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From: Arnd Bergmann <arnd@arndb.de>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Johannes Berg <johannes.berg@intel.com>,
	Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
	Luca Coelho <luciano.coelho@intel.com>,
	Intel Linux Wireless <linuxwifi@intel.com>,
	Kalle Valo <kvalo@codeaurora.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH] iwlwifi: mvm: Use div64_s64 instead of do_div in iwl_mvm_debug_range_resp
Date: Wed, 20 Feb 2019 11:51:34 +0100	[thread overview]
Message-ID: <CAK8P3a1d6Zksdv-Or+paawyn4N0u4EpVw9QgyDGHYvX_1s3JrQ@mail.gmail.com> (raw)
In-Reply-To: <20190219182105.19933-1-natechancellor@gmail.com>

On Tue, Feb 19, 2019 at 7:22 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>

> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/ftm-initiator.c b/drivers/net/wireless/intel/iwlwifi/mvm/ftm-initiator.c
> index e9822a3ec373..92b22250eb7d 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/ftm-initiator.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/ftm-initiator.c
> @@ -462,7 +462,7 @@ static void iwl_mvm_debug_range_resp(struct iwl_mvm *mvm, u8 index,
>  {
>         s64 rtt_avg = res->ftm.rtt_avg * 100;
>
> -       do_div(rtt_avg, 6666);
> +       div64_s64(rtt_avg, 6666);

This is wrong: div64_s64 does not modify its argument like do_div(), but
it returns the result instead. You also don't want to divide by a 64-bit
value when the second argument is a small constant.

I think the correct way should be

       s64 rtt_avg = div_s64(res->ftm.rtt_avg * 100, 6666);

If you know that the value is positive, using unsigned types
and div_u64() would be slightly faster.

      Arnd

  parent reply	other threads:[~2019-02-20 10:51 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-19 18:21 [PATCH] iwlwifi: mvm: Use div64_s64 instead of do_div in iwl_mvm_debug_range_resp Nathan Chancellor
2019-02-19 19:05 ` Nick Desaulniers
2019-02-20  9:39   ` Luca Coelho
2019-02-20 10:51 ` Arnd Bergmann [this message]
2019-02-20 17:56   ` Nathan Chancellor
2019-02-21  7:33     ` Luciano Coelho
2019-02-21  8:06 ` [PATCH v2] iwlwifi: mvm: Use div_s64 " Nathan Chancellor
2019-02-22  0:13   ` Nick Desaulniers
2019-02-22  7:45     ` Luciano Coelho
2019-02-22  8:52     ` Arnd Bergmann

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