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Documentation: irq/concepts: Minor improvements

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Just note in the docs:

 1) A PCI device as an example for shared interrupts
 2) A sparse tree can be used for interrupts too
 3) i8259s which have 8 pins

[ tglx: Fix up subject prefix ]

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250319092951.37667-55-jirislaby@kernel.org
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Jiri Slaby (SUSE) 2025-03-19 10:29:47 +01:00 committed by Thomas Gleixner
parent 2f7bd3293e
commit 225942f06e
1 changed files with 7 additions and 5 deletions
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Documentation/core-api/irq/concepts.rst
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@ -4,18 +4,20 @@ What is an IRQ?
An IRQ is an interrupt request from a device. Currently, they can come
in over a pin, or over a packet. Several devices may be connected to
the same pin thus sharing an IRQ.
the same pin thus sharing an IRQ. Such as on legacy PCI bus: All devices
typically share 4 lanes/pins. Note that each device can request an
interrupt on each of the lanes.
An IRQ number is a kernel identifier used to talk about a hardware
interrupt source. Typically, this is an index into the global irq_desc
array, but except for what linux/interrupt.h implements, the details
are architecture specific.
array or sparse_irqs tree. But except for what linux/interrupt.h
implements, the details are architecture specific.
An IRQ number is an enumeration of the possible interrupt sources on a
machine. Typically, what is enumerated is the number of input pins on
all of the interrupt controllers in the system. In the case of ISA,
what is enumerated are the 16 input pins on the two i8259 interrupt
controllers.
what is enumerated are the 8 input pins on each of the two i8259
interrupt controllers.
Architectures can assign additional meaning to the IRQ numbers, and
are encouraged to in the case where there is any manual configuration