linux-kernel - Re: [PATCH] brcmfmac: cfg80211: use msecs_to

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Message-ID: <1426596159.23897.61.camel@perches.com>
Date:	Tue, 17 Mar 2015 05:42:39 -0700
From:	Joe Perches <joe@...ches.com>
To:	Nicholas Mc Guire <hofrat@...dl.org>
Cc:	Brett Rudley <brudley@...adcom.com>,
	Arend van Spriel <arend@...adcom.com>,
	"Franky (Zhenhui) Lin" <frankyl@...adcom.com>,
	Hante Meuleman <meuleman@...adcom.com>,
	Kalle Valo <kvalo@...eaurora.org>,
	"John W. Linville" <linville@...driver.com>,
	Pieter-Paul Giesberts <pieterpg@...adcom.com>,
	Daniel Kim <dekim@...adcom.com>,
	Johannes Berg <johannes.berg@...el.com>,
	linux-wireless@...r.kernel.org, brcm80211-dev-list@...adcom.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] brcmfmac: cfg80211: use msecs_to_jiffies for time
 conversion

On Tue, 2015-03-17 at 08:06 -0400, Nicholas Mc Guire wrote:
> Converting milliseconds to jiffies by "val * HZ / 1000" is technically
> OK but msecs_to_jiffies(val) is the cleaner solution and handles all
> corner cases correctly. This is a minor API consolidation only and
> should make things more readable.

Hi Nicholas

These API consolidation changes now always have a function
call when the compiler may have previously been able to
optimize out the "constant * HZ / 1000" calculation.

Perhaps the [um]secs_to_jiffies calls should be indirected
with yet another static inline with a __builtin_constant_p()
test so that the function calls can again be avoided when
possible.

(and a trivial style note)

> diff --git a/drivers/net/wireless/brcm80211/brcmfmac/cfg80211.c b/drivers/net/wireless/brcm80211/brcmfmac/cfg80211.c
[]
> @@ -1110,7 +1110,7 @@ brcmf_cfg80211_escan(struct wiphy *wiphy, struct brcmf_cfg80211_vif *vif,
>  
>  	/* Arm scan timeout timer */
>  	mod_timer(&cfg->escan_timeout, jiffies +
> -			WL_ESCAN_TIMER_INTERVAL_MS * HZ / 1000);
> +		  msecs_to_jiffies(WL_ESCAN_TIMER_INTERVAL_MS));

It may be nicer to keep the arithmetic on one line

 	mod_timer(&cfg->escan_timeout,
		  jiffies + msecs_to_jiffies(WL_ESCAN_TIMER_INTERVAL_MS));


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