On 2/16/06, Bahadir Balban <bilgehan.balban@xxxxxxxxx> wrote:
> Hi,
>
> As of 2.6.14, in include/linux/irq.h, there are two definitions as below.
>
> As you see, hw_interrupt_type accepts irq numbers for each irq,
> whereas irq_desc does not seem to keep a unique number. How are the
> two matched to each other then? Is it the irq_desc array offset that
> uniquely identifies each irq?
yes its the irq_desc array offset which uniquly identifies the irq. Do
see the "do_IRQ()" function. IRQ number received by CPU is pushed on
the process specific kernel stack before calling the do_IRQ(), When
do_IRQ() is called, it pulls out this number from stack and uses that
as an index in array irq_desc strucuture. Each entry in this array is
of irq_desc type, which is a structure, each entry contains the
pointer to hardware specific structure of function pointers (this is
what you mentioned : hw_interrupt_type), its the handle element of
irq_desc structure. Function pointers in hardware specific structure
are used for enabling, disabling, acknowledging the interrupts to PIC.
Hope that clears your doubts.
>
> I am asking because on some (e.g. smp) architectures, there are
> multiple irq controllers and each irq number does `not' represent a
> primary key for each irq, because there are multiple instances of the
> same irq number on the system, for different irqs.
I am not sure if SMP system have one than on set of PICs. As far as I
know, there is one set of advanced IO PIC, which actually route the
system interrupts to different internal AIOPICs embedded in CPUs.
-Gaurav
>
> Thanks,
> Bahadir
>
> /*
> * Interrupt controller descriptor. This is all we need
> * to describe about the low-level hardware.
> */
> struct hw_interrupt_type {
> const char * typename;
> unsigned int (*startup)(unsigned int irq);
> void (*shutdown)(unsigned int irq);
> void (*enable)(unsigned int irq);
> void (*disable)(unsigned int irq);
> void (*ack)(unsigned int irq);
> /*...*/
> };
>
> /*
> * This is the "IRQ descriptor", which contains various information
> * about the irq, including what kind of hardware handling it has,
> * whether it is disabled etc etc.
> */
> typedef struct irq_desc {
> hw_irq_controller *handler;
> void *handler_data;
> struct irqaction *action; /* IRQ action list */
> unsigned int status; /* IRQ status */
> unsigned int depth; /* nested irq disables */
> unsigned int irq_count; /* For detecting broken interrupts */
> unsigned int irqs_unhandled;
> spinlock_t lock;
> /* ... */
> }
>
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>
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