MIPS: Cavium OCTEON multiplier state preservation.

For OCTEON, implement a save and restore of the multiplier state
across context switches.
Signed-off-by: Tomaso Paoletti <tpaoletti@caviumnetworks.com>
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/stackframe.h

@@ -194,6 +194,19 @@
 		LONG_S	$31, PT_R31(sp)
 		ori	$28, sp, _THREAD_MASK
 		xori	$28, _THREAD_MASK
+#ifdef CONFIG_CPU_CAVIUM_OCTEON
+		.set    mips64
+		pref    0, 0($28)       /* Prefetch the current pointer */
+		pref    0, PT_R31(sp)   /* Prefetch the $31(ra) */
+		/* The Octeon multiplier state is affected by general multiply
+		    instructions. It must be saved before and kernel code might
+		    corrupt it */
+		jal     octeon_mult_save
+		LONG_L  v1, 0($28)  /* Load the current pointer */
+			 /* Restore $31(ra) that was changed by the jal */
+		LONG_L  ra, PT_R31(sp)
+		pref    0, 0(v1)    /* Prefetch the current thread */
+#endif
 		.set	pop
 		.endm
 
@@ -324,6 +337,10 @@
 		DVPE	5				# dvpe a1
 		jal	mips_ihb
 #endif /* CONFIG_MIPS_MT_SMTC */
+#ifdef CONFIG_CPU_CAVIUM_OCTEON
+		/* Restore the Octeon multiplier state */
+		jal	octeon_mult_restore
+#endif
 		mfc0	a0, CP0_STATUS
 		ori	a0, STATMASK
 		xori	a0, STATMASK