From fa8223db1d69e6de9c7c7210804e8bb284067954 Mon Sep 17 00:00:00 2001 From: Helge Deller Date: Sat, 29 Jun 2013 13:24:16 +0200 Subject: parisc: document the shadow registers commit a83f58bcb24003b9de2364de7c829a263423ead7 upstream. Signed-off-by: Helge Deller Signed-off-by: Greg Kroah-Hartman --- Documentation/parisc/registers | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'Documentation') diff --git a/Documentation/parisc/registers b/Documentation/parisc/registers index dd3caddd1ad9..10c7d1730f5d 100644 --- a/Documentation/parisc/registers +++ b/Documentation/parisc/registers @@ -77,6 +77,14 @@ PSW default E value 0 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. -- cgit v1.2.3