Hi Dave, I have confirmed the execution has go into desc <http://lxr.linux.no/linux+*/+code=desc>->irq_data <http://lxr.linux.no/linux+*/+code=irq_data>.chip <http://lxr.linux.no/linux+*/+code=chip>->irq_disable <http://lxr.linux.no/linux+*/+code=irq_disable>(&desc <http://lxr.linux.no/linux+*/+code=desc>->irq_data <http://lxr.linux.no/linux+*/+code=irq_data>); However, irq_disable points to kernel/irq/chip.c:default_disable() which do nothings. Unlike default_enable() which called by enable_irq() will unmask the IRQ accordingly. I don't understand the reason behind. BR, Jacky On 3/3/2011 6:49 AM, Dave Hylands wrote:

Hi Jacky,

Sending to the list as well.

On Tue, Mar 1, 2011 at 1:55 AM, Jacky Lam<lamshuyin@gmail.com> wrote:

...

Hi,

It's long before when I want to enable/disable an interrupt, I call enable_irq()/disable_irq(). However, recently, I do that again. disable_irq() do nothing. I looked into the code and find disable_irq() is pointing to a empty function default_disable(). This change is started from 2.6.20.

I want to know what should I do if I want to disable an interrupt now? So disable/enable_irq are nestable, and you're expected to call them in the order disable/enable.

You need to call enable_irq exactly the same number of times that you call disable_irq.

If you start wth inerrtupts enabled and do enable_irq ...do some stuff... disable_irq

then disable_irq will do nothing since it just decremented the count that enable_irq incremented.

Another way of looking at it is that disable_irq increments a count, and enable_irq decrements a count. The interrupt is only "really" disabled when the count transitions from 0 to 1, and the interrupt is only "really" enabled when the count transitions from 1 to 0.

Dave Hylands