[PATCH] enic: fix adaptive irq coalescing on 32-bit

[PATCH] enic: fix adaptive irq coalescing on 32-bit

[Arnd Bergmann]

7c2ce6e60f703 "enic: Add support for adaptive interrupt coalescing"
introduced a 64-bit division that causes a link error on all 32-bit
machines:

drivers/built-in.o: In function `enic_poll_msix':
:(.text+0x54ff00): undefined reference to `__aeabi_uldivmod'

Since we are dividing another 32-bit value and are only interested
in the approximate range here, it should always be safe to limit
the delta to an u32 value.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
----
I haven't seen another report of this bug, just ignore this
mail if it was already fixed.

Also, there may be better ways to solve this.

diff --git a/drivers/net/ethernet/cisco/enic/enic_main.c b/drivers/net/ethernet/cisco/enic/enic_main.c
index 0d8995c..ad2fac2 100644
--- a/drivers/net/ethernet/cisco/enic/enic_main.c
+++ b/drivers/net/ethernet/cisco/enic/enic_main.c
@@ -1217,7 +1217,7 @@ static void enic_calc_int_moderation(struct enic *enic, struct vnic_rq *rq)
 	 */
 
 	traffic <<= 3;
-	traffic /= delta;
+	traffic /= min_t(u32, delta, UINT_MAX);
 
 	for (index = 0; index < ENIC_MAX_COALESCE_TIMERS; index++)
 		if (traffic < mod_table[index].rx_rate)

RE: [PATCH] enic: fix adaptive irq coalescing on 32-bit

[David Laight]

From: Arnd Bergmann
> 7c2ce6e60f703 "enic: Add support for adaptive interrupt coalescing"
> introduced a 64-bit division that causes a link error on all 32-bit
> machines:
> 
> drivers/built-in.o: In function `enic_poll_msix':
> :(.text+0x54ff00): undefined reference to `__aeabi_uldivmod'
> 
> Since we are dividing another 32-bit value and are only interested
> in the approximate range here, it should always be safe to limit
> the delta to an u32 value.
...
>  	traffic <<= 3;
> -	traffic /= delta;
> +	traffic /= min_t(u32, delta, UINT_MAX);

I suspect that doesn't have the desired effect.
I think it is the same as:
	traffic /= (u32)delta;
If you was the correct value for large 'delta' then maybe:
	traffic = delta > UINT_MAX ? 0 : traffic / (u32)delta;

	David

Re: [PATCH] enic: fix adaptive irq coalescing on 32-bit

[Arnd Bergmann]

On Friday 23 May 2014 08:29:52 David Laight wrote:
> From: Arnd Bergmann
> > 7c2ce6e60f703 "enic: Add support for adaptive interrupt coalescing"
> > introduced a 64-bit division that causes a link error on all 32-bit
> > machines:
> > 
> > drivers/built-in.o: In function `enic_poll_msix':
> > :(.text+0x54ff00): undefined reference to `__aeabi_uldivmod'
> > 
> > Since we are dividing another 32-bit value and are only interested
> > in the approximate range here, it should always be safe to limit
> > the delta to an u32 value.
> ...
> >  	traffic <<= 3;
> > -	traffic /= delta;
> > +	traffic /= min_t(u32, delta, UINT_MAX);
> 
> I suspect that doesn't have the desired effect.
> I think it is the same as:
> 	traffic /= (u32)delta;

Ah, you are right, sorry for that.

> If you was the correct value for large 'delta' then maybe:
> 	traffic = delta > UINT_MAX ? 0 : traffic / (u32)delta;

That looks better, yes.

	Arnd