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Documentation: Update IRQ-domain.txt to document irq_domain_mapping

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irq_domain_mapping is a rather useful tool to understand how IRqs
are mapped in irqdomains, and yet it is not documented anywhere.
Let's address this.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: http://lkml.kernel.org/r/20170512115538.10767-5-marc.zyngier@arm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Marc Zyngier 2017-05-12 12:55:38 +01:00 committed by Thomas Gleixner
parent a97b852b4d
commit 5328666939
1 changed files with 39 additions and 2 deletions
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41
Documentation/IRQ-domain.txt
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@ -231,5 +231,42 @@ needs to:
4) No need to implement irq_domain_ops.map and irq_domain_ops.unmap,
they are unused with hierarchy irq_domain.
Hierarchy irq_domain may also be used to support other architectures,
such as ARM, ARM64 etc.
Hierarchy irq_domain is in no way x86 specific, and is heavily used to
support other architectures, such as ARM, ARM64 etc.
=== Debugging ===
If you switch on CONFIG_IRQ_DOMAIN_DEBUG (which depends on
CONFIG_IRQ_DOMAIN and CONFIG_DEBUG_FS), you will find a new file in
your debugfs mount point, called irq_domain_mapping. This file
contains a live snapshot of all the IRQ domains in the system:
name mapped linear-max direct-max devtree-node
pl061 8 8 0 /smb/gpio@e0080000
pl061 8 8 0 /smb/gpio@e1050000
pMSI 0 0 0 /interrupt-controller@e1101000/v2m@e0080000
MSI 37 0 0 /interrupt-controller@e1101000/v2m@e0080000
GICv2m 37 0 0 /interrupt-controller@e1101000/v2m@e0080000
GICv2 448 448 0 /interrupt-controller@e1101000
it also iterates over the interrupts to display their mapping in the
domains, and makes the domain stacking visible:
irq hwirq chip name chip data active type domain
1 0x00019 GICv2 0xffff00000916bfd8 * LINEAR GICv2
2 0x0001d GICv2 0xffff00000916bfd8 LINEAR GICv2
3 0x0001e GICv2 0xffff00000916bfd8 * LINEAR GICv2
4 0x0001b GICv2 0xffff00000916bfd8 * LINEAR GICv2
5 0x0001a GICv2 0xffff00000916bfd8 LINEAR GICv2
[...]
96 0x81808 MSI 0x (null) RADIX MSI
96+ 0x00063 GICv2m 0xffff8003ee116980 RADIX GICv2m
96+ 0x00063 GICv2 0xffff00000916bfd8 LINEAR GICv2
97 0x08800 MSI 0x (null) * RADIX MSI
97+ 0x00064 GICv2m 0xffff8003ee116980 * RADIX GICv2m
97+ 0x00064 GICv2 0xffff00000916bfd8 * LINEAR GICv2
Here, interrupts 1-5 are only using a single domain, while 96 and 97
are build out of a stack of three domain, each level performing a
particular function.