Re: Devices, IRQs and handlers

[Vijay Subramanian <subramanian.vijay@xxxxxxxxx>]

Hi,
Please see below.
vijay

On 09/01/06, Rajaram Suryanarayanan <rajaram_linux@xxxxxxxxx> wrote:
> Hi,
>
> I am confused about the mapping between devices, IRQs and the handlers. I am
> following Robert Love's "Linux Kernel Development" book.
>


> 1. I see that different handlers can share the same IRQ with SA_SHIRQ flag.
> So does it mean there can be different interrupt handlers for the same
> device...? As I think each device has a unique IRQ ( strict 1-to-1 mapping
> between device and its IRQ ).
>


No. It means that different devices can share an interrupt.   All the
devices need to
set SA_SHIRQ flag for sharing to work. Each device will have only 1 interrupt.
Each device type i.e every model has a unique dev id.
Each device will have a unique IRQ (hardware interrupt).
try cat /proc/interrupts. Some interrupts will be shared.

> 2. Related to the first question, can different devices share the same IRQ ?
>
yes. If all have SA_SHIRQ enabled. If the first device does not enable sharing,
no other devices can use the interrupt.
> 3. Regarding dev_id parameter, is it unique to each device ? I mean is each
> device has a strict 1-to-1 mapping with dev_id ?
>

see above
> Please explain.
>
> Thanks,
> Rajaram.
>
>
>
hope this helps. someone please correct me if anything is wrong.
-vijay
>
>
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--
Networks Lab, RPI
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