Blackfin arch: add an option to allow people to stick exception stack into L1 scratch

allow people to stick exception stack into L1 scratch
and make sure it gets placed into .bss sections rather than .data
Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

arch/blackfin/Kconfig

@@ -667,6 +667,17 @@ config APP_STACK_L1
 
 	  Currently only works with FLAT binaries.
 
+config EXCEPTION_L1_SCRATCH
+	bool "Locate exception stack in L1 Scratch Memory"
+	default n
+	depends on !APP_STACK_L1 && !SYSCALL_TAB_L1
+	help
+	  Whenever an exception occurs, use the L1 Scratch memory for
+	  stack storage.  You cannot place the stacks of FLAT binaries
+	  in L1 when using this option.
+
+	  If you don't use L1 Scratch, then you should say Y here.
+
 comment "Speed Optimizations"
 config BFIN_INS_LOWOVERHEAD
 	bool "ins[bwl] low overhead, higher interrupt latency"

arch/blackfin/mach-common/entry.S

@@ -1539,14 +1539,23 @@ ENTRY(_sys_call_table)
 	.endr
 END(_sys_call_table)
 
-_exception_stack:
-	.rept 1024
-	.long 0;
-	.endr
-_exception_stack_top:
-
 #if ANOMALY_05000261
 /* Used by the assembly entry point to work around an anomaly.  */
 _last_cplb_fault_retx:
 	.long 0;
 #endif
+
+#ifdef CONFIG_EXCEPTION_L1_SCRATCH
+/* .section .l1.bss.scratch */
+.set _exception_stack_top, L1_SCRATCH_START + L1_SCRATCH_LENGTH
+#else
+#ifdef CONFIG_SYSCALL_TAB_L1
+.section .l1.bss
+#else
+.bss
+#endif
+_exception_stack:
+.size _exception_stack, 1024 * 4
+.set _exception_stack_top, _exception_stack + 1024 * 4
+.size _exception_stack_top, 0
+#endif