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    Subject[PATCH] irq_domain: Standardise legacy/linear domain selection
    Date
    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 <broonie@opensource.wolfsonmicro.com>
    ---
    Documentation/IRQ-domain.txt | 5 +++++
    include/linux/irqdomain.h | 5 +++++
    kernel/irq/irqdomain.c | 30 ++++++++++++++++++++++++++++++
    3 files changed, 40 insertions(+)

    diff --git a/Documentation/IRQ-domain.txt b/Documentation/IRQ-domain.txt
    index 27dcaab..1401cec 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 ====
    +irq_domain_add_simple()
    irq_domain_add_legacy()
    irq_domain_add_legacy_isa()

    @@ -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
    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.
    diff --git a/include/linux/irqdomain.h b/include/linux/irqdomain.h
    index 5abb533e..17b60be 100644
    --- a/include/linux/irqdomain.h
    +++ b/include/linux/irqdomain.h
    @@ -112,6 +112,11 @@ struct irq_domain {
    };

    #ifdef CONFIG_IRQ_DOMAIN
    +struct irq_domain *irq_domain_add_simple(struct device_node *of_node,
    + unsigned int size,
    + unsigned int first_irq,
    + const struct irq_domain_ops *ops,
    + void *host_data);
    struct irq_domain *irq_domain_add_legacy(struct device_node *of_node,
    unsigned int size,
    unsigned int first_irq,
    diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
    index d3968e9..0c51958 100644
    --- a/kernel/irq/irqdomain.c
    +++ b/kernel/irq/irqdomain.c
    @@ -140,6 +140,36 @@ static unsigned int irq_domain_legacy_revmap(struct irq_domain *domain,
    }

    /**
    + * irq_domain_add_simple() - Allocate and register a simple irq_domain.
    + * @of_node: pointer to interrupt controller's device tree node.
    + * @size: total number of irqs in mapping
    + * @first_irq: first number of irq block assigned to the domain
    + * @ops: map/unmap domain callbacks
    + * @host_data: Controller private data pointer
    + *
    + * Allocates a legacy irq_domain if irq_base is positive or a linear
    + * domain otherwise.
    + *
    + * This is intended to implement the expected behaviour for most
    + * interrupt controllers which is that a linear mapping should
    + * normally be used unless the system requires a legacy mapping in
    + * order to support supplying interrupt numbers during non-DT
    + * registration of devices.
    + */
    +struct irq_domain *irq_domain_add_simple(struct device_node *of_node,
    + unsigned int size,
    + unsigned int first_irq,
    + const struct irq_domain_ops *ops,
    + void *host_data)
    +{
    + if (first_irq > 0)
    + return irq_domain_add_legacy(of_node, size, first_irq, 0,
    + ops, host_data);
    + else
    + return irq_domain_add_linear(of_node, size, ops, host_data);
    +}
    +
    +/**
    * irq_domain_add_legacy() - Allocate and register a legacy revmap irq_domain.
    * @of_node: pointer to interrupt controller's device tree node.
    * @size: total number of irqs in legacy mapping
    --
    1.7.10


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