xtensa: keep a3 and excsave1 on entry to exception handlers

Based on the SMP patch by Joe Taylor and subsequent fixes.
Preserve exception table pointer (normally stored in excsave1 SR) as it
cannot be easily restored in SMP environment.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>

arch/xtensa/include/asm/regs.h

@@ -82,6 +82,7 @@
 #define PS_CALLINC_SHIFT	16
 #define PS_CALLINC_MASK		0x00030000
 #define PS_OWB_SHIFT		8
+#define PS_OWB_WIDTH		4
 #define PS_OWB_MASK		0x00000F00
 #define PS_RING_SHIFT		6
 #define PS_RING_MASK		0x000000C0

arch/xtensa/kernel/align.S

@@ -146,9 +146,9 @@
  *   a0:	trashed, original value saved on stack (PT_AREG0)
  *   a1:	a1
  *   a2:	new stack pointer, original in DEPC
- *   a3:	dispatch table
+ *   a3:	a3
  *   depc:	a2, original value saved on stack (PT_DEPC)
- *   excsave_1:	a3
+ *   excsave_1:	dispatch table
  *
  *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
  *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
@@ -171,7 +171,6 @@ ENTRY(fast_unaligned)
 	s32i	a8, a2, PT_AREG8
 
 	rsr	a0, depc
-	xsr	a3, excsave1
 	s32i	a0, a2, PT_AREG2
 	s32i	a3, a2, PT_AREG3
 

arch/xtensa/kernel/coprocessor.S

@@ -32,9 +32,9 @@
  *   a0:	trashed, original value saved on stack (PT_AREG0)
  *   a1:	a1
  *   a2:	new stack pointer, original in DEPC
- *   a3:	dispatch table
+ *   a3:	a3
  *   depc:	a2, original value saved on stack (PT_DEPC)
- *   excsave_1:	a3
+ *   excsave_1:	dispatch table
  *
  *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
  *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
@@ -225,9 +225,9 @@ ENDPROC(coprocessor_restore)
  *   a0:	trashed, original value saved on stack (PT_AREG0)
  *   a1:	a1
  *   a2:	new stack pointer, original in DEPC
- *   a3:	dispatch table
+ *   a3:	a3
  *   depc:	a2, original value saved on stack (PT_DEPC)
- *   excsave_1:	a3
+ *   excsave_1:	dispatch table
  *
  *   PT_DEPC >= VALID_DOUBLE_EXCEPTION_ADDRESS: double exception, DEPC
  *	     <  VALID_DOUBLE_EXCEPTION_ADDRESS: regular exception
@@ -245,7 +245,6 @@ ENTRY(fast_coprocessor)
 
 	/* Save remaining registers a1-a3 and SAR */
 
-	xsr	a3, excsave1
 	s32i	a3, a2, PT_AREG3
 	rsr	a3, sar
 	s32i	a1, a2, PT_AREG1