Registering shared & unshared interrupt handlers

Registering shared & unshared interrupt handlers

[Jay Aurabind]

Dear all,

I've been going through Robert Love's LKD. Here is an excerpt from it
regarding registration of interrupt handlers:

"When request_irq() is called with IRQF_SHARED specified, the call
succeeds only if the interrupt line is currently not registered, or if
all registered handlers on the line also specified IRQF_SHARED. Shared
handlers, however, can mix usage of IRQF_DISABLED."

As far as I understand, the first sentence tells that a line currently
having shared handlers *will only have* handlers registered with
IRQF_SHARED flag in the past. Correct ?

If a interrupt line has been registered by a handler specified as non
shared, then whats the point in allowing a new handler with a "shared"
flag registering to the same line ? So how does the mixing of shared and
unshared interrupt handlers for the same line go together as mentioned
by the 2nd sentence ?

Or does it mean that a shared handler which already succeeded the
registration can further register a non shared and shared interrupt
handlers? ( That doesnt make sense, but still... )  ? Simply put, can
someone please elaborate on the second sentence I quoted from the book ?


Thanks and Regards,
Aurabindo J
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Registering shared & unshared interrupt handlers

[Jay Aurabind]

Oops, I though IRQ_DISABLED was the opposite of IRQF_SHARED. Sorry.
Consider the question not asked :P


On 17 February 2014 12:06, Jay Aurabind <jay.aurabind@gmail.com> wrote:

>  Dear all,
>
> I've been going through Robert Love's LKD. Here is an excerpt from it
> regarding registration of interrupt handlers:
>
> "When request_irq() is called with IRQF_SHARED specified, the call
> succeeds only if the interrupt line is currently not registered, or if all
> registered handlers on the line also specified IRQF_SHARED. Shared
> handlers, however, can mix usage of IRQF_DISABLED."
>
> As far as I understand, the first sentence tells that a line currently
> having shared handlers *will only have* handlers registered with
> IRQF_SHARED flag in the past. Correct ?
>
> If a interrupt line has been registered by a handler specified as non
> shared, then whats the point in allowing a new handler with a "shared" flag
> registering to the same line ? So how does the mixing of shared and
> unshared interrupt handlers for the same line go together as mentioned by
> the 2nd sentence ?
>
> Or does it mean that a shared handler which already succeeded the
> registration can further register a non shared and shared interrupt
> handlers? ( That doesnt make sense, but still... )  ? Simply put, can
> someone please elaborate on the second sentence I quoted from the book ?
>
>
> Thanks and Regards,
> Aurabindo J
>



-- 

Thanks and Regards,
*Aurabindo J*
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Registering shared & unshared interrupt handlers

[anish singh]

On Sun, Feb 16, 2014 at 10:36 PM, Jay Aurabind <jay.aurabind@gmail.com> wrote:
> Dear all,
>
> I've been going through Robert Love's LKD. Here is an excerpt from it
> regarding registration of interrupt handlers:
>
> "When request_irq() is called with IRQF_SHARED specified, the call succeeds
> only if the interrupt line is currently not registered, or if all registered
> handlers on the line also specified IRQF_SHARED. Shared handlers, however,
> can mix usage of IRQF_DISABLED."
>
> As far as I understand, the first sentence tells that a line currently
> having shared handlers *will only have* handlers registered with IRQF_SHARED
> flag in the past. Correct ?

Yes.
>
> If a interrupt line has been registered by a handler specified as non
> shared, then whats the point in allowing a new handler with a "shared" flag
It doesn't allow as your statement in above indicates.

> registering to the same line ? So how does the mixing of shared and unshared
> interrupt handlers for the same line go together as mentioned by the 2nd
> sentence ?
>
> Or does it mean that a shared handler which already succeeded the
> registration can further register a non shared and shared interrupt
> handlers? ( That doesnt make sense, but still... )  ? Simply put, can
> someone please elaborate on the second sentence I quoted from the book ?

Where is the confusion ? Just to be clear, kernel doesn't allow shared
and unshared
interrupt handler on the same interrupt line. Read the code in irq
core subsystem.
kernel/kernel/irq
>
>
> Thanks and Regards,
> Aurabindo J
>
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