Introduce bus_get_bus_tag() method

Provide bus_get_bus_tag() for sparc64, powerpc, arm, arm64 and mips
nexus and its children in order to return a platform specific default tag.

This is required to ensure generic correctness of the bus_space tag.
It is especially needed for arches where child bus tag does not match
the parent bus tag. This solves the problem with ppc architecture
where the PCI bus tag differs from parent bus tag which is big-endian.

This commit is a part of the following patch:
https://reviews.freebsd.org/D4879

Submitted by:  Marcin Mazurek <mma@semihalf.com>
Obtained from: Semihalf
Sponsored by:  Annapurna Labs
Reviewed by:   jhibbits, mmel
Differential Revision: https://reviews.freebsd.org/D4879

1 files changed, 11 insertions, 0 deletions

diff --git a/sys/kern/bus_if.m b/sys/kern/bus_if.m
index e55b1ce9ea6b..8acadd7c10b7 100644
--- a/sys/kern/bus_if.m
+++ b/sys/kern/bus_if.m
@@ -637,6 +637,17 @@ METHOD bus_dma_tag_t get_dma_tag {
 } DEFAULT bus_generic_get_dma_tag;
 
 /**
+ * @brief Returns bus_space_tag_t for use w/ devices on the bus.
+ *
+ * @param _dev		the parent device of @p _child
+ * @param _child	the device to which the tag will belong
+ */
+METHOD bus_space_tag_t get_bus_tag {
+	device_t	_dev;
+	device_t	_child;
+} DEFAULT bus_generic_get_bus_tag;
+
+/**
  * @brief Allow the bus to determine the unit number of a device.
  *
  * @param _dev		the parent device of @p _child