ARC: Process-creation/scheduling/idle-loop
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/arc/kernel/fpu.c b/arch/arc/kernel/fpu.c
new file mode 100644
index 0000000..f352e51
--- /dev/null
+++ b/arch/arc/kernel/fpu.c
@@ -0,0 +1,55 @@
+/*
+ * fpu.c - save/restore of Floating Point Unit Registers on task switch
+ *
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/sched.h>
+#include <asm/switch_to.h>
+
+/*
+ * To save/restore FPU regs, simplest scheme would use LR/SR insns.
+ * However since SR serializes the pipeline, an alternate "hack" can be used
+ * which uses the FPU Exchange insn (DEXCL) to r/w FPU regs.
+ *
+ * Store to 64bit dpfp1 reg from a pair of core regs:
+ * dexcl1 0, r1, r0 ; where r1:r0 is the 64 bit val
+ *
+ * Read from dpfp1 into pair of core regs (w/o clobbering dpfp1)
+ * mov_s r3, 0
+ * daddh11 r1, r3, r3 ; get "hi" into r1 (dpfp1 unchanged)
+ * dexcl1 r0, r1, r3 ; get "low" into r0 (dpfp1 low clobbered)
+ * dexcl1 0, r1, r0 ; restore dpfp1 to orig value
+ *
+ * However we can tweak the read, so that read-out of outgoing task's FPU regs
+ * and write of incoming task's regs happen in one shot. So all the work is
+ * done before context switch
+ */
+
+void fpu_save_restore(struct task_struct *prev, struct task_struct *next)
+{
+ unsigned int *saveto = &prev->thread.fpu.aux_dpfp[0].l;
+ unsigned int *readfrom = &next->thread.fpu.aux_dpfp[0].l;
+
+ const unsigned int zero = 0;
+
+ __asm__ __volatile__(
+ "daddh11 %0, %2, %2\n"
+ "dexcl1 %1, %3, %4\n"
+ : "=&r" (*(saveto + 1)), /* early clobber must here */
+ "=&r" (*(saveto))
+ : "r" (zero), "r" (*(readfrom + 1)), "r" (*(readfrom))
+ );
+
+ __asm__ __volatile__(
+ "daddh22 %0, %2, %2\n"
+ "dexcl2 %1, %3, %4\n"
+ : "=&r"(*(saveto + 3)), /* early clobber must here */
+ "=&r"(*(saveto + 2))
+ : "r" (zero), "r" (*(readfrom + 3)), "r" (*(readfrom + 2))
+ );
+}