linux-kernel - [PATCH RFC] genirq: Genric chip: Use DIV_ROUND

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Date:	Fri, 05 Jul 2013 17:13:12 +0800
From:	Axel Lin <axel.lin@...ics.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Tony Lindgren <tony@...mide.com>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: [PATCH RFC] genirq: Genric chip: Use DIV_ROUND_UP to count 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.

Signed-off-by: Axel Lin <axel.lin@...ics.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



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