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-rw-r--r--Documentation/IRQ-domain.txt41
1 files changed, 39 insertions, 2 deletions
diff --git a/Documentation/IRQ-domain.txt b/Documentation/IRQ-domain.txt
index 82001a25a14b..1f246eb25ca5 100644
--- a/Documentation/IRQ-domain.txt
+++ b/Documentation/IRQ-domain.txt
@@ -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.