Blackfin arch: allow people to select the feature that is unavailable to the kernel

- allow people to select the feature that is unavailable to the kernel: NMI, JTAG, or CYCLES.
 - change default NMI handler to simply dump hardware trace buffer.
 - remove default NMI handler completely as calling into kernel code is not safe
   move example handler to wiki so people dont haphazardly copy and paste this stuff thinking its safe

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>

arch/blackfin/Kconfig

@@ -521,6 +521,52 @@ config BFIN_IDLE_LED_NUM
 	help
 	  Select the LED (marked on the board) for you to blink.
 
+choice
+	prompt "Blackfin Exception Scratch Register"
+	default BFIN_SCRATCH_REG_RETN
+	help
+	  Select the resource to reserve for the Exception handler:
+	    - RETN: Non-Maskable Interrupt (NMI)
+	    - RETE: Exception Return (JTAG/ICE)
+	    - CYCLES: Performance counter
+
+	  If you are unsure, please select "RETN".
+
+config BFIN_SCRATCH_REG_RETN
+	bool "RETN"
+	help
+	  Use the RETN register in the Blackfin exception handler
+	  as a stack scratch register.  This means you cannot
+	  safely use NMI on the Blackfin while running Linux, but
+	  you can debug the system with a JTAG ICE and use the
+	  CYCLES performance registers.
+
+	  If you are unsure, please select "RETN".
+
+config BFIN_SCRATCH_REG_RETE
+	bool "RETE"
+	help
+	  Use the RETE register in the Blackfin exception handler
+	  as a stack scratch register.  This means you cannot
+	  safely use a JTAG ICE while debugging a Blackfin board,
+	  but you can safely use the CYCLES performance registers
+	  and the NMI.
+
+	  If you are unsure, please select "RETN".
+
+config BFIN_SCRATCH_REG_CYCLES
+	bool "CYCLES"
+	help
+	  Use the CYCLES register in the Blackfin exception handler
+	  as a stack scratch register.  This means you cannot
+	  safely use the CYCLES performance registers on a Blackfin
+	  board at anytime, but you can debug the system with a JTAG
+	  ICE and use the NMI.
+
+	  If you are unsure, please select "RETN".
+
+endchoice
+
 #
 # Sorry - but you need to put the hex address here -
 #

arch/blackfin/kernel/irqchip.c

@@ -98,9 +98,8 @@ int show_interrupts(struct seq_file *p, void *v)
  */
 
 #ifdef CONFIG_DO_IRQ_L1
-asmlinkage void asm_do_IRQ(unsigned int irq, struct pt_regs *regs)__attribute__((l1_text));
+__attribute__((l1_text))
 #endif
-
 asmlinkage void asm_do_IRQ(unsigned int irq, struct pt_regs *regs)
 {
 	struct pt_regs *old_regs;

arch/blackfin/mach-bf533/head.S

@@ -53,10 +53,12 @@ __INIT
 ENTRY(__start)
 	/* R0: argument of command line string, passed from uboot, save it */
 	R7 = R0;
-	/* Set the SYSCFG register:
+	/* Enable Cycle Counter and Nesting Of Interrupts */
-	 * Enable Cycle Counter and Nesting Of Interrupts (3rd Bit)
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
-	 */
+	R0 = SYSCFG_SNEN;
-	R0 = 0x36;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
 	SYSCFG = R0;
 	R0 = 0;
 

arch/blackfin/mach-bf537/head.S

@@ -51,10 +51,12 @@ __INIT
 ENTRY(__start)
 	/* R0: argument of command line string, passed from uboot, save it */
 	R7 = R0;
-	/* Set the SYSCFG register:
+	/* Enable Cycle Counter and Nesting Of Interrupts */
-	 * Enable Cycle Counter and Nesting Of Interrupts (3rd Bit)
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
-	 */
+	R0 = SYSCFG_SNEN;
-	R0 = 0x36;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
 	SYSCFG = R0;
 	R0 = 0;
 

arch/blackfin/mach-bf548/head.S

@@ -50,9 +50,13 @@ ENTRY(__start)
 ENTRY(__stext)
 	/* R0: argument of command line string, passed from uboot, save it */
 	R7 = R0;
-	/* Set the SYSCFG register */
+	/* Enable Cycle Counter and Nesting Of Interrupts */
-	R0 = 0x36;
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
-	SYSCFG = R0;   /*Enable Cycle Counter and Nesting Of Interrupts(3rd Bit)*/
+	R0 = SYSCFG_SNEN;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
+	SYSCFG = R0;
 	R0 = 0;
 
 	/* Clear Out All the data and pointer  Registers*/

arch/blackfin/mach-bf561/head.S

@@ -51,10 +51,12 @@ __INIT
 ENTRY(__start)
 	/* R0: argument of command line string, passed from uboot, save it */
 	R7 = R0;
-	/* Set the SYSCFG register:
+	/* Enable Cycle Counter and Nesting Of Interrupts */
-	 * Enable Cycle Counter and Nesting Of Interrupts (3rd Bit)
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
-	 */
+	R0 = SYSCFG_SNEN;
-	R0 = 0x36;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
 	SYSCFG = R0;
 	R0 = 0;
 

arch/blackfin/mach-common/entry.S

@@ -58,6 +58,14 @@
 
 #include <asm/mach-common/context.S>
 
+#if defined(CONFIG_BFIN_SCRATCH_REG_RETN)
+# define EX_SCRATCH_REG RETN
+#elif defined(CONFIG_BFIN_SCRATCH_REG_RETE)
+# define EX_SCRATCH_REG RETE
+#else
+# define EX_SCRATCH_REG CYCLES
+#endif
+
 #ifdef CONFIG_EXCPT_IRQ_SYSC_L1
 .section .l1.text
 #else
@@ -93,7 +101,7 @@ ENTRY(_ex_icplb)
 	call __cplb_hdr;
 	DEBUG_START_HWTRACE(p5, r7)
 	RESTORE_ALL_SYS
-	SP = RETN;
+	SP = EX_SCRATCH_REG;
 	rtx;
 ENDPROC(_ex_icplb)
 
@@ -102,7 +110,7 @@ ENTRY(_ex_syscall)
 	(R7:6,P5:4) = [sp++];
 	ASTAT = [sp++];
 	raise 15;		/* invoked by TRAP #0, for sys call */
-	sp = retn;
+	sp = EX_SCRATCH_REG;
 	rtx
 ENDPROC(_ex_syscall)
 
@@ -145,7 +153,7 @@ _return_from_exception:
 #endif
 	(R7:6,P5:4) = [sp++];
 	ASTAT = [sp++];
-	sp = retn;
+	sp = EX_SCRATCH_REG;
 	rtx;
 ENDPROC(_ex_soft_bp)
 
@@ -204,7 +212,7 @@ ENTRY(_ex_trap_c)
 	DEBUG_START_HWTRACE(p5, r7)
 	(R7:6,P5:4) = [sp++];
 	ASTAT = [sp++];
-	SP = RETN;
+	SP = EX_SCRATCH_REG;
 	raise 5;
 	rtx;
 ENDPROC(_ex_trap_c)
@@ -279,7 +287,7 @@ ENTRY(_trap) /* Exception: 4th entry into system event table(supervisor mode)*/
 	 * covered by a CPLB.  Switch to an exception stack; use RETN as a
 	 * scratch register (for want of a better option).
 	 */
-	retn = sp;
+	EX_SCRATCH_REG = sp;
 	sp.l = _exception_stack_top;
 	sp.h = _exception_stack_top;
 	/* Try to deal with syscalls quickly.  */

arch/blackfin/mach-common/interrupt.S

@@ -177,27 +177,15 @@ ENTRY(_evt_ivhw)
 	jump .Lcommon_restore_context;
 #endif
 
-/* interrupt routine for evt2 - 2.  This is NMI.  */
+/* Interrupt routine for evt2 (NMI).
-ENTRY(_evt_evt2)
+ * We don't actually use this, so just return.
-	SAVE_CONTEXT
+ * For inner circle type details, please see:
-#ifdef CONFIG_FRAME_POINTER
+ * http://docs.blackfin.uclinux.org/doku.php?id=linux:nmi
-	fp = 0;
+ */
-#endif
+ENTRY(_evt_nmi)
-#if ANOMALY_05000283
+.weak _evt_nmi
-	cc = r7 == r7;
-	p5.h = 0xffc0;
-	p5.l = 0x0014;
-	if cc jump 1f;
-	r7.l = W[p5];
-1:
-#endif
-	r0 = IRQ_NMI;
-	r1 =  sp;
-	SP += -12;
-	call _asm_do_IRQ;
-	SP += 12;
-	RESTORE_CONTEXT
 	rtn;
+ENDPROC(_evt_nmi)
 
 /* interrupt routine for core timer - 6 */
 ENTRY(_evt_timer)

arch/blackfin/mach-common/ints-priority-dc.c

@@ -362,7 +362,11 @@ void __init init_exception_vectors(void)
 {
 	SSYNC();
 
-	bfin_write_EVT2(evt_evt2);
+	/* cannot program in software:
+	 * evt0 - emulation (jtag)
+	 * evt1 - reset
+	 */
+	bfin_write_EVT2(evt_nmi);
 	bfin_write_EVT3(trap);
 	bfin_write_EVT5(evt_ivhw);
 	bfin_write_EVT6(evt_timer);

arch/blackfin/mach-common/ints-priority-sc.c

@@ -721,7 +721,11 @@ void __init init_exception_vectors(void)
 {
 	SSYNC();
 
-	bfin_write_EVT2(evt_evt2);
+	/* cannot program in software:
+	 * evt0 - emulation (jtag)
+	 * evt1 - reset
+	 */
+	bfin_write_EVT2(evt_nmi);
 	bfin_write_EVT3(trap);
 	bfin_write_EVT5(evt_ivhw);
 	bfin_write_EVT6(evt_timer);

include/asm-blackfin/irq_handler.h

@@ -1,12 +1,15 @@
 #ifndef _IRQ_HANDLER_H
 #define _IRQ_HANDLER_H
 
+#include <linux/types.h>
+#include <linux/linkage.h>
+
 /* BASE LEVEL interrupt handler routines */
 asmlinkage void evt_exception(void);
 asmlinkage void trap(void);
 asmlinkage void evt_ivhw(void);
 asmlinkage void evt_timer(void);
-asmlinkage void evt_evt2(void);
+asmlinkage void evt_nmi(void);
 asmlinkage void evt_evt7(void);
 asmlinkage void evt_evt8(void);
 asmlinkage void evt_evt9(void);