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author | Linus Torvalds <torvalds@linux-foundation.org> | 2012-12-11 19:30:08 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-12-11 19:30:08 (GMT) |
commit | 259cdbee2094d28b72f0f3d77bc9203d682994ff (patch) | |
tree | de2017bda15cce950d96ef6d1771dd7e7fbab490 /Documentation | |
parent | 9ada9fd5dfaf0076eadf42cecc68f7adc1717c58 (diff) | |
parent | 023bba36387de704b3ea2a69bf9f9ed2301cfbcc (diff) | |
download | linux-fsl-qoriq-259cdbee2094d28b72f0f3d77bc9203d682994ff.tar.xz |
Merge tag 'irqdomain-for-linus' of git://git.secretlab.ca/git/linux-2.6
Pull irqdomain changes from Grant Likely:
"Trivial changes to irqdomain. An update to the documentation and make
one of the error paths not quite so obnoxious."
* tag 'irqdomain-for-linus' of git://git.secretlab.ca/git/linux-2.6:
irqdomain: update documentation
irqdomain: stop screaming about preallocated irqdescs
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/IRQ-domain.txt | 34 |
1 files changed, 33 insertions, 1 deletions
diff --git a/Documentation/IRQ-domain.txt b/Documentation/IRQ-domain.txt index 1401cec..9bc9594 100644 --- a/Documentation/IRQ-domain.txt +++ b/Documentation/IRQ-domain.txt @@ -7,6 +7,21 @@ systems with multiple interrupt controllers the kernel must ensure that each one gets assigned non-overlapping allocations of Linux IRQ numbers. +The number of interrupt controllers registered as unique irqchips +show a rising tendency: for example subdrivers of different kinds +such as GPIO controllers avoid reimplementing identical callback +mechanisms as the IRQ core system by modelling their interrupt +handlers as irqchips, i.e. in effect cascading interrupt controllers. + +Here the interrupt number loose all kind of correspondence to +hardware interrupt numbers: whereas in the past, IRQ numbers could +be chosen so they matched the hardware IRQ line into the root +interrupt controller (i.e. the component actually fireing the +interrupt line to the CPU) nowadays this number is just a number. + +For this reason we need a mechanism to separate controller-local +interrupt numbers, called hardware irq's, from Linux IRQ numbers. + The irq_alloc_desc*() and irq_free_desc*() APIs provide allocation of irq numbers, but they don't provide any support for reverse mapping of the controller-local IRQ (hwirq) number into the Linux IRQ number @@ -40,6 +55,10 @@ required hardware setup. When an interrupt is received, irq_find_mapping() function should be used to find the Linux IRQ number from the hwirq number. +The irq_create_mapping() function must be called *atleast once* +before any call to irq_find_mapping(), lest the descriptor will not +be allocated. + If the driver has the Linux IRQ number or the irq_data pointer, and needs to know the associated hwirq number (such as in the irq_chip callbacks) then it can be directly obtained from irq_data->hwirq. @@ -119,4 +138,17 @@ numbers. 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. +system and will otherwise use a linear domain mapping. The semantics +of this call are such that if an IRQ range is specified then +descriptors will be allocated on-the-fly for it, and if no range is +specified it will fall through to irq_domain_add_linear() which meand +*no* irq descriptors will be allocated. + +A typical use case for simple domains is where an irqchip provider +is supporting both dynamic and static IRQ assignments. + +In order to avoid ending up in a situation where a linear domain is +used and no descriptor gets allocated it is very important to make sure +that the driver using the simple domain call irq_create_mapping() +before any irq_find_mapping() since the latter will actually work +for the static IRQ assignment case. |