[PATCH] cs5535-clockevt: allow the MFGPT IRQ to be shared
From: Jens Rottmann
Date: Thu Dec 22 2011 - 11:35:57 EST
cs5535-clockevt: allow the MFGPT IRQ to be shared
Shared timer IRQs are not a good solution, however the Geode platform has no
APIC, IRQs are a scarce resource and there is no technical reason to forbid it
rightaway. Increased latencies and overhead due to sharing are still better
than a driver refusing to load.
Signed-off-by: Jens Rottmann <JRottmann@xxxxxxxxxxxxxxxxxx>
---
Hi,
I tested this a bit longer, this time with MFGPT IRQ actually being triggered,
with cs5535-clockevt driver loaded first or second when sharing the IRQ, with
some CPU load or without.
I didn't encounter any negative effects of this change. I did have suspend
problems with cs5535-clockevt, but that was in no way different from before I
applied this patch, it's an unrelated BIOS issue.
Thomas Gleixner wrote:
> No, you can share a timer irq. The other drivers don't have the SHARED
> flag set because they are on exclusive irq lines, ...
Is this an ACK?
> shared irqs suck and you figure that out once you try to
> use that shared timer irq on a preempt-rt enabled kernel.
Or a NACK? :-| (I did address this in the commit log.)
The kernel I tested with was 3.2-rc6, CONFIG_SMP=y and CONFIG_PREEMPT=y. As I
said, I didn't notice anything bad happening.
Thanks and have a nice christmas holiday,
Jens
--- linux-3.2-rc6/drivers/clocksource/cs5535-clockevt.c
+++ allow_shared_mfgpt_irq/drivers/clocksource/cs5535-clockevt.c
@@ -133,7 +133,7 @@ static irqreturn_t mfgpt_tick(int irq, v
static struct irqaction mfgptirq = {
.handler = mfgpt_tick,
- .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER,
+ .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED,
.name = DRV_NAME,
};
_
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