[PATCH RFC] genirq: Genric chip: Use DIV_ROUND_UP to count numchips

[PATCH RFC] genirq: Genric chip: Use DIV_ROUND_UP to count numchips

[Axel Lin]

The number of interrupts in a domain may be not divisible by the number of
interrupts each chip handles.
Integer division may truncate the result, thus use DIV_ROUND_UP to count
numchips.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
---
Seems all users of irq_alloc_domain_generic_chips() in current code do not
have this issue. I just found the issue while reading the code.

In the commit 02c981c0 of "ARM: CSR: Adding CSR SiRFprimaII board support"
It set SIRFSOC_INTENAL_IRQ_END to 59.
So I think this might be a possible case for some hardware.

 kernel/irq/generic-chip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/irq/generic-chip.c b/kernel/irq/generic-chip.c
index 10e663a..452d6f2 100644
--- a/kernel/irq/generic-chip.c
+++ b/kernel/irq/generic-chip.c
@@ -275,7 +275,7 @@ int irq_alloc_domain_generic_chips(struct irq_domain *d, int irqs_per_chip,
 	if (d->gc)
 		return -EBUSY;
 
-	numchips = d->revmap_size / irqs_per_chip;
+	numchips = DIV_ROUND_UP(d->revmap_size, irqs_per_chip);
 	if (!numchips)
 		return -EINVAL;
 
-- 
1.8.1.2

[tip:irq/urgent] genirq: generic chip: Use DIV_ROUND_UP to calculate numchips

[tip-bot for Axel Lin]

Commit-ID:  002fca5df168922103a2bb52748f9984e6de80b2
Gitweb:     http://git.kernel.org/tip/002fca5df168922103a2bb52748f9984e6de80b2
Author:     Axel Lin <axel.lin@ingics.com>
AuthorDate: Fri, 5 Jul 2013 17:13:12 +0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 5 Jul 2013 11:39:25 +0200

genirq: generic chip: Use DIV_ROUND_UP to calculate numchips

The number of interrupts in a domain may be not divisible by the
number of interrupts each chip handles. Integer division may truncate
the result, thus use DIV_ROUND_UP to count numchips.

Seems all users of irq_alloc_domain_generic_chips() in current code do
not have this issue. I just found the issue while reading the code.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Link: http://lkml.kernel.org/r/1373015592.18252.2.camel@phoenix
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/irq/generic-chip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/irq/generic-chip.c b/kernel/irq/generic-chip.c
index 1c39ecc..2f274f3 100644
--- a/kernel/irq/generic-chip.c
+++ b/kernel/irq/generic-chip.c
@@ -278,7 +278,7 @@ int irq_alloc_domain_generic_chips(struct irq_domain *d, int irqs_per_chip,
 	if (d->revmap_type != IRQ_DOMAIN_MAP_LINEAR)
 		return -EINVAL;
 
-	numchips = d->revmap_data.linear.size / irqs_per_chip;
+	numchips = DIV_ROUND_UP(d->revmap_data.linear.size, irqs_per_chip);
 	if (!numchips)
 		return -EINVAL;