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

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

[Nicholas Mc Guire]

API compliance scanning with coccinelle flagged:

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.

Patch was compile tested for x86_64_defconfig (implies CONFIG_USB_IRDA=m)

Patch is against 4.1-rc4 (localversion-next is -next-20150519)

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---
 drivers/net/irda/irda-usb.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/irda/irda-usb.c b/drivers/net/irda/irda-usb.c
index f6c9163..f3e4563 100644
--- 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)));
+
 		return;
 	}
 	
-- 
1.7.10.4

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

[Joe Perches]

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.

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

[David Miller]

From: Joe Perches <joe@perches.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.

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

[Joe Perches]

On Tue, 2015-05-19 at 16:45 -0400, David Miller wrote:
> From: Joe Perches <joe@perches.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

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

[Guenter Roeck]

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:
> > From: Joe Perches <joe@perches.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
> 
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

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

[Joe Perches]

On Tue, 2015-05-19 at 18:44 -0700, Guenter Roeck wrote:
> On Tue, May 19, 2015 at 02:09:07PM -0700, Joe Perches wrote:
> > 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 conversions
> to 0 in the kernel.

Thanks Guenter

Nope, you're not mistaken.

Non 0 constants always return a value > 0

The existing uses like max(1ul, msecs_to_jiffies(<variable>))
just guard against <variable> being 0.

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

[David Miller]

From: Nicholas Mc Guire <hofrat@osadl.org>
Date: Sat, 23 May 2015 14:46:30 +0200

> API compliance scanning with coccinelle flagged:
> 
> 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.
> 
> Patch was compile tested for x86_64_defconfig (implies CONFIG_USB_IRDA=m)
> 
> Patch is against 4.1-rc4 (localversion-next is -next-20150522)
> 
> Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>

Applied to net-next, thanks.

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

[Nicholas Mc Guire]

API compliance scanning with coccinelle flagged:

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.

Patch was compile tested for x86_64_defconfig (implies CONFIG_USB_IRDA=m)

Patch is against 4.1-rc4 (localversion-next is -next-20150522)

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

V2: the unnecessary () flagged by Joe Perches <joe@perches.com>
    was removed - thanks (...once again...) !

 drivers/net/irda/irda-usb.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/irda/irda-usb.c b/drivers/net/irda/irda-usb.c
index f6c9163..f3e4563 100644
--- 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));
+
 		return;
 	}
 	
-- 
1.7.10.4