CODEWITHSUNDEEP
linuxlinux-kernellinux-device-driver
Dien Nguyen
Dien Nguyen

Reputation: 2059

request_irq to be handled by a single CPU

I would like to ask if there is a way to register the interrupt handler so that only one cpu will handle this interrupt line. The problem is that we have a function that can be called in both normal context and interrupt context. In this function we use irqs_disabled() to check the caller context. If the caller context is interrupt, we switch the processing to polling mode (continuously check the interrupt status register). Although the irqs_disabled() tells that the local interrupt of current CPU is disabled, the interrupt handler is still called by other CPUs and hence the interrupt status register are cleared in the interrupt handler. The polling code now checks the wrong value of the interrupt status register and do wrong processing.

Upvotes: 0

Views: 1181

Answers (2)

gby
gby

Reputation: 15218

You're doing it wrong. Don't limit your interrupt to be handled by a single CPU - instead use a spin_lock_irqsave to protect the code path. This will work both on the same CPU and across CPUs.

See http://www.mjmwired.net/kernel/Documentation/spinlocks.txt for the relevant API and here is a nice article from Linux Journal that explain the usage: http://www.linuxjournal.com/article/5833

Upvotes: 4

Arlie Stephens
Arlie Stephens

Reputation: 1176

I've got no experience with ARM, but on x86 you can arrange for a particular interrupt to be called on only one processor via /proc/irq/<number>/smp_affinity - set from user space - replacing the number with irq you care about - and this looks as if it's essentially generic. Note that the value you set it to is a bit mask, expressed in hex, without a leading 0x. I.e. if you want cpu 0, set it to 1, for cpu 1, set it to 2, etc. Beware of a process called irqbalance, which uses this mechanism, and might well override whatever you have done.

But why are you doing this? If you want to know whether you are called from an interrupt, there's an interface available named something like in_interrupt(). I've used it to avoid trying to call blocking functions from code that might be called from interrupt context.

Upvotes: 1

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