How kernel derive irq number for particular irq line

How kernel derive irq number for particular irq line

[Abhinav Misra]

Hi Guys,

I want to know how the irq number is derived in linux kernel.
In kernel we are using below function for registering ISR.

int *request_threaded_irq*(unsigned int irq, irq_handler_t handler,
irq_handler_t thread_fn, unsigned long irqflags, const char *devname,
void *dev_id)

1st arg is irq number. Now suppose for an i2c device, want to
configure an interrupt then we can enable interrupt by configuring the
particular register
but from where we will get the irq number details.

Do we as a programmer need to map it ?

Please provide your views.

BR,Abhinav
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How kernel derive irq number for particular irq line

[Greg KH]

On Mon, Jun 25, 2018 at 12:17:06AM +0530, Abhinav Misra wrote:
> Hi Guys,
> 
> I want to know how the irq number is derived in linux kernel.

It all depends on your platform.  It either comes from the firmware/bios
or it is in the device tree information.  The kernel itself doesn't know
this information, it has to be told that from an external source.

Hope this helps,

greg k-h

How kernel derive irq number for particular irq line

[priyaranjan]

Hi Abhinav,

On Mon, Jun 25, 2018 at 12:17 AM, Abhinav Misra
<abhitheextremeeng@gmail.com> wrote:
> Hi Guys,
>
> I want to know how the irq number is derived in linux kernel.
> In kernel we are using below function for registering ISR.
>

For platform drivers, usually this information comes from the device tree entry.
which you get originally from the System On chip HW interface documents or
from specification sheets.

> int request_threaded_irq(unsigned int irq, irq_handler_t handler,
> irq_handler_t thread_fn, unsigned long irqflags, const char *devname, void
> *dev_id)
>
> 1st arg is irq number. Now suppose for an i2c device, want to configure an
> interrupt then we can enable interrupt by configuring the particular
> register
> but from where we will get the irq number details.

In kernel drivers, DT entries of that driver are read
by some APIs and then used by request_irq

>
> Do we as a programmer need to map it ?
>
> Please provide your views.
>
> BR,Abhinav
>
>
>
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