xtensa: remap io area defined in device tree

Use the simple-bus node to discover the io area, and remap the cached and
bypass io ranges. The parent-bus-address value of the first triplet in the
"ranges" property is used. This value is rounded down to the nearest 256MB
boundary. The length of the io area is fixed at 256MB; the "ranges" property
length value is ignored.

Other limitations: (1) only the first simple-bus node is considered, and (2)
only the first triplet of the "ranges" property is considered.

See ePAPR 1.1 §6.5 for the simple-bus node description, and §2.3.8 for the
"ranges" property description.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/xtensa/mmu.txt b/Documentation/xtensa/mmu.txt
index 2b1af7606d57..0312fe66475c 100644
--- a/Documentation/xtensa/mmu.txt
+++ b/Documentation/xtensa/mmu.txt
@@ -44,3 +44,21 @@ After step 4, we jump to intended (linked) address of this code.
  40..5F -> 40         40..5F -> pc  -> pc  40..5F -> pc
  20..3F -> 20  -> 20  20..3F -> 20
  00..1F -> 00  -> 00  00..1F -> 00
+
+The default location of IO peripherals is above 0xf0000000. This may change
+using a "ranges" property in a device tree simple-bus node. See ePAPR 1.1, §6.5
+for details on the syntax and semantic of simple-bus nodes. The following
+limitations apply:
+
+1. Only top level simple-bus nodes are considered
+
+2. Only one (first) simple-bus node is considered
+
+3. Empty "ranges" properties are not supported
+
+4. Only the first triplet in the "ranges" property is considered
+
+5. The parent-bus-address value is rounded down to the nearest 256MB boundary
+
+6. The IO area covers the entire 256MB segment of parent-bus-address; the
+   "ranges" triplet length field is ignored