path: root/Documentation/IRQ-domain.txt
diff options
authorMark Brown <>2012-07-05 12:19:19 +0100
committerGrant Likely <>2012-07-11 14:59:17 +0100
commit781d0f46d81e2c26c70649903b503bcfe817efc8 (patch)
tree11794b64c41e8468db6d14243c5becce3b5b64c8 /Documentation/IRQ-domain.txt
parentaed98048bd1c83469d96932c1901e867d9ba519a (diff)
irq_domain: Standardise legacy/linear domain selection
A large proportion of interrupt controllers that support legacy mappings do so because non-DT systems need to use fixed IRQ numbers when registering devices via buses but can otherwise use a linear mapping. The interrupt controller itself typically is not affected by the mapping used and best practice is to use a linear mapping where possible so drivers frequently select at runtime depending on if a legacy range has been allocated to them. Standardise this behaviour by providing irq_domain_register_simple() which will allocate a linear mapping unless a positive first_irq is provided in which case it will fall back to a legacy mapping. This helps make best practice for irq_domain adoption clearer. Signed-off-by: Mark Brown <> Signed-off-by: Grant Likely <>
Diffstat (limited to 'Documentation/IRQ-domain.txt')
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/IRQ-domain.txt b/Documentation/IRQ-domain.txt
index 27dcaabfb4db..1401cece745a 100644
--- a/Documentation/IRQ-domain.txt
+++ b/Documentation/IRQ-domain.txt
@@ -93,6 +93,7 @@ Linux IRQ number into the hardware.
Most drivers cannot use this mapping.
==== Legacy ====
@@ -115,3 +116,7 @@ The legacy map should only be used if fixed IRQ mappings must be
supported. For example, ISA controllers would use the legacy map for
mapping Linux IRQs 0-15 so that existing ISA drivers get the correct IRQ
+Most users of legacy mappings should use irq_domain_add_simple() which
+will use a legacy domain only if an IRQ range is supplied by the
+system and will otherwise use a linear domain mapping.