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>

10 files changed, 103 insertions, 44 deletions

diff --git a/arch/blackfin/Kconfig b/arch/blackfin/Kconfig
index cdce8cc..26ebb0e 100644
--- a/arch/blackfin/Kconfig
+++ b/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 -
 #
diff --git a/arch/blackfin/kernel/irqchip.c b/arch/blackfin/kernel/irqchip.c
index 462ae41..73647c1 100644
--- a/arch/blackfin/kernel/irqchip.c
+++ b/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;
diff --git a/arch/blackfin/mach-bf533/head.S b/arch/blackfin/mach-bf533/head.S
index 1d5b9db..3be6fee 100644
--- a/arch/blackfin/mach-bf533/head.S
+++ b/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 (3rd Bit)
-	 */
-	R0 = 0x36;
+	/* Enable Cycle Counter and Nesting Of Interrupts */
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
+	R0 = SYSCFG_SNEN;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
 	SYSCFG = R0;
 	R0 = 0;
 
diff --git a/arch/blackfin/mach-bf537/head.S b/arch/blackfin/mach-bf537/head.S
index 6dbcb77..0836bfd 100644
--- a/arch/blackfin/mach-bf537/head.S
+++ b/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 (3rd Bit)
-	 */
-	R0 = 0x36;
+	/* Enable Cycle Counter and Nesting Of Interrupts */
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
+	R0 = SYSCFG_SNEN;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
 	SYSCFG = R0;
 	R0 = 0;
 
diff --git a/arch/blackfin/mach-bf548/head.S b/arch/blackfin/mach-bf548/head.S
index 4c7d49f..937fbef 100644
--- a/arch/blackfin/mach-bf548/head.S
+++ b/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 */
-	R0 = 0x36;
-	SYSCFG = R0;   /*Enable Cycle Counter and Nesting Of Interrupts(3rd Bit)*/
+	/* Enable Cycle Counter and Nesting Of Interrupts */
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
+	R0 = SYSCFG_SNEN;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
+	SYSCFG = R0;
 	R0 = 0;
 
 	/* Clear Out All the data and pointer  Registers*/
diff --git a/arch/blackfin/mach-bf561/head.S b/arch/blackfin/mach-bf561/head.S
index 8c9f73b..139f4cf 100644
--- a/arch/blackfin/mach-bf561/head.S
+++ b/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 (3rd Bit)
-	 */
-	R0 = 0x36;
+	/* Enable Cycle Counter and Nesting Of Interrupts */
+#ifdef CONFIG_BFIN_SCRATCH_REG_CYCLES
+	R0 = SYSCFG_SNEN;
+#else
+	R0 = SYSCFG_SNEN | SYSCFG_CCEN;
+#endif
 	SYSCFG = R0;
 	R0 = 0;
 
diff --git a/arch/blackfin/mach-common/entry.S b/arch/blackfin/mach-common/entry.S
index ab278a7..2188f81 100644
--- a/arch/blackfin/mach-common/entry.S
+++ b/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.  */
diff --git a/arch/blackfin/mach-common/interrupt.S b/arch/blackfin/mach-common/interrupt.S
index 1d5ba5e..c6b32fe 100644
--- a/arch/blackfin/mach-common/interrupt.S
+++ b/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.  */
-ENTRY(_evt_evt2)
-	SAVE_CONTEXT
-#ifdef CONFIG_FRAME_POINTER
-	fp = 0;
-#endif
-#if ANOMALY_05000283
-	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
+/* Interrupt routine for evt2 (NMI).
+ * We don't actually use this, so just return.
+ * For inner circle type details, please see:
+ * http://docs.blackfin.uclinux.org/doku.php?id=linux:nmi
+ */
+ENTRY(_evt_nmi)
+.weak _evt_nmi
 	rtn;
+ENDPROC(_evt_nmi)
 
 /* interrupt routine for core timer - 6 */
 ENTRY(_evt_timer)
diff --git a/arch/blackfin/mach-common/ints-priority-dc.c b/arch/blackfin/mach-common/ints-priority-dc.c
index 684d306..2db3546 100644
--- a/arch/blackfin/mach-common/ints-priority-dc.c
+++ b/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);
diff --git a/arch/blackfin/mach-common/ints-priority-sc.c b/arch/blackfin/mach-common/ints-priority-sc.c
index a2016af..d3b7672 100644
--- a/arch/blackfin/mach-common/ints-priority-sc.c
+++ b/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);