netdev - Re: [PATCH] irda: irda-usb: use msecs_to

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Message-Id: <20150519.164555.1631069770118420652.davem@davemloft.net>
Date:	Tue, 19 May 2015 16:45:55 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	joe@...ches.com
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

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.

Agreed.
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