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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