[PATCH v2 14/14] Documentation: Update irq_domain.rst with new lookup APIs

Marc Zyngier
2021-08-02T16:57:04Z

Catch up with the recent irqdomain updates, and document
{generic_,}handle_domain_irq(), irq_resolve_mapping() as well
as the deprecation of some of the older APIs.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
Documentation/core-api/irq/irq-domain.rst | 28 ++++++++++++++++++++---
1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/Documentation/core-api/irq/irq-domain.rst b/Documentation/core-api/irq/irq-domain.rst
index 53283b3729a1..6979b4af2c1f 100644
--- a/Documentation/core-api/irq/irq-domain.rst
+++ b/Documentation/core-api/irq/irq-domain.rst
@@ -55,8 +55,24 @@ exist then it will allocate a new Linux irq_desc, associate it with
the hwirq, and call the .map() callback so the driver can perform any
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.
+Once a mapping has been established, it can be retrieved or used via a
+variety of methods:
+
+- irq_resolve_mapping() returns a pointer to the irq_desc structure
+ for a given domain and hwirq number, and NULL if there was no
+ mapping.
+- irq_find_mapping() returns a Linux IRQ number for a given domain and
+ hwirq number, and 0 if there was no mapping
+- irq_linear_revmap() is now identical to irq_find_mapping(), and is
+ deprecated
+- generic_handle_domain_irq() handles an interrupt described by a
+ domain and a hwirq number
+- handle_domain_irq() does the same thing for root interrupt
+ controllers and deals with the set_irq_reg()/irq_enter() sequences
+ that most architecture requires
+
+Note that irq domain lookups must happen in contexts that are
+compatible with a RCU read-side critical section.

The irq_create_mapping() function must be called *atleast once*
before any call to irq_find_mapping(), lest the descriptor will not
@@ -137,7 +153,9 @@ required. Calling irq_create_direct_mapping() will allocate a Linux
IRQ number and call the .map() callback so that driver can program the
Linux IRQ number into the hardware.

-Most drivers cannot use this mapping.
+Most drivers cannot use this mapping, and it is now gated on the
+CONFIG_IRQ_DOMAIN_NOMAP option. Please refrain from introducing new
+users of this API.

Legacy
------
@@ -157,6 +175,10 @@ for IRQ numbers that are passed to struct device registrations. In that
case the Linux IRQ numbers cannot be dynamically assigned and the legacy
mapping should be used.

+As the name implies, the *_legacy() functions are deprecated and only
+exist to ease the support of ancient platforms. No new users should be
+added.
+
The legacy map assumes a contiguous range of IRQ numbers has already
been allocated for the controller and that the IRQ number can be
calculated by adding a fixed offset to the hwirq number, and
--
2.30.2