linux-kernel - Re: [PATCH] irda: irda-usb: use msecs_to

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Message-ID: <1432069747.2870.215.camel@perches.com>
Date:	Tue, 19 May 2015 14:09:07 -0700
From:	Joe Perches <joe@...ches.com>
To:	David Miller <davem@...emloft.net>
Cc:	hofrat@...dl.org, samuel@...tiz.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irda: irda-usb: use msecs_to_jiffies for conversions

On Tue, 2015-05-19 at 16:45 -0400, David Miller wrote:
> From: Joe Perches <joe@...ches.com>
> Date: Tue, 19 May 2015 07:32:15 -0700
> 
> > On Tue, 2015-05-19 at 12:51 +0200, Nicholas Mc Guire wrote:
> >> Converting milliseconds to jiffies by "val * HZ / 1000" is technically
> >> is not a clean solution as it does not handle all corner cases correctly.
> >> By changing the conversion to use msecs_to_jiffies(val) conversion is
> >> correct in all cases.
> >> 
> >> in the current code: 
> >>   mod_timer(&self->rx_defer_timer, jiffies + (10 * HZ / 1000));
> >> for HZ < 100 (e.g. CONFIG_HZ == 64|32 in alpha) this effectively results 
> >> in no delay at all.
> > []
> >> diff --git a/drivers/net/irda/irda-usb.c b/drivers/net/irda/irda-usb.c
> > []
> >> @@ -848,7 +848,9 @@ static void irda_usb_receive(struct urb *urb)
> >>  		 * Jean II */
> >>  		self->rx_defer_timer.function = irda_usb_rx_defer_expired;
> >>  		self->rx_defer_timer.data = (unsigned long) urb;
> >> -		mod_timer(&self->rx_defer_timer, jiffies + (10 * HZ / 1000));
> >> +		mod_timer(&self->rx_defer_timer,
> >> +			  jiffies + (msecs_to_jiffies(10)));
> > 
> > The unnecessary () around msecs_to_jiffies could be removed.

The other thing that could be done is to use
	max(1ul, msecs_to_jiffies())
so that there's always some delay even if HZ <= 50



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