Re: [PATCH] irda: irda-usb: use msecs_to_jiffies for conversions

On Tue, May 19, 2015 at 02:09:07PM -0700, Joe Perches wrote:

On Tue, 2015-05-19 at 16:45 -0400, David Miller wrote:

quoted

From: Joe Perches <joe@perches.com>
Date: Tue, 19 May 2015 07:32:15 -0700

quoted

On Tue, 2015-05-19 at 12:51 +0200, Nicholas Mc Guire wrote:

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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.

[]

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diff --git a/drivers/net/irda/irda-usb.c b/drivers/net/irda/irda-usb.c

[]

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@@ -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

I may be mistaken, but I am quite sure that msecs_to_jiffies() always returns
at least 1 in such situations. Otherwise there would be lots of converstions
to 0 in the kernel.

Guenter