Rajendra Stalekar wrote:
Rajendra :- How can that be done? Is it not a physical interrupt line(wire),
how can that line go to multiple devices.
That is the job of interrupt controller in the hardware- it multiplexes
the interrupt sources and presents them on the single interrupt number
IRQ number shown in /proc/interrupts. The way it is implemented in the
hardware differs for each architecture. When dealing with the shared
interrupts, the interrupt handler for each device driver needs to know
what hardware device caused the interrupt by means of dev_id argument
which must be unique for every device that claims the same interrupt
line (IRQ number) - hence every shared interrupt handler checks if the
interrupt was caused by the device it supports and handles the interrupt
only if it is from its device - otherwise the interrupt handler should
return IRQ_NONE and possibly let another (correct) device driver handle
the interrupt and return IRQ_HANDLED.
I can understand during driver initialization it's not a good idea to
install the handler because we don't know whether we are going to use the
device.
But if we install the handler when the device is opened how can we share
the
interrupt line because it is now dedicated for it.
If I understand the question correctly - this is done when registering
the interrupt handler. If shared interrupt line is used, every interrupt
handler that claims the same IRQ number must use SA_SHIRQ in the flags
argument. That being said it doesn't really matter which driver claims
the shared line first as long as all of them are using SA_SHIRQ in their
flags.
Correct me if I'm wrong...
best regards,
hinko
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