path: root/Documentation/parisc
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authorHelge Deller <deller@gmx.de>2013-06-29 13:24:16 +0200
committerHelge Deller <deller@gmx.de>2013-07-09 22:09:19 +0200
commita83f58bcb24003b9de2364de7c829a263423ead7 (patch)
tree1d6a4d3d0664dffdd3bcff0a2c305e4ad2581682 /Documentation/parisc
parent30a9f0b251285ba29f09a7134eee07a4c3aca639 (diff)
parisc: document the shadow registers
Signed-off-by: Helge Deller <deller@gmx.de> Cc: <stable@vger.kernel.org> # 3.10
Diffstat (limited to 'Documentation/parisc')
1 files changed, 8 insertions, 0 deletions
diff --git a/Documentation/parisc/registers b/Documentation/parisc/registers
index dd3caddd1ad9..10c7d1730f5d 100644
--- a/Documentation/parisc/registers
+++ b/Documentation/parisc/registers
@@ -78,6 +78,14 @@ Shadow Registers used by interruption handler code
TOC enable bit 1
+The PA-RISC architecture defines 7 registers as "shadow registers".
+Those are used in RETURN FROM INTERRUPTION AND RESTORE instruction to reduce
+the state save and restore time by eliminating the need for general register
+(GR) saves and restores in interruption handlers.
+Shadow registers are the GRs 1, 8, 9, 16, 17, 24, and 25.
Register usage notes, originally from John Marvin, with some additional
notes from Randolph Chung.

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