ARM: Allow to mask data aborts

Sometimes it's useful to test if a memory operation works or
aborts. This adds data_abort_mask() to ignore data aborts and
data_abort_unmask() to enable them again. This is used in the
next step for the 'md' command so that illegal addresses just
show 'xxxxxxxx' instead of crashing the system.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

arch/arm/cpu/exceptions.S

@@ -88,6 +88,21 @@
 	movs	pc, lr
 	.endm
 
+	.macro try_data_abort
+	ldr	r13, =arm_ignore_data_abort	@ check try mode
+	ldr	r13, [r13]
+	cmp	r13, #0
+	beq	do_abort_\@
+	ldr	r13, =arm_data_abort_occurred
+	str	r13, [r13]
+	mrs	r13, spsr			@ read saved CPSR
+	tst	r13, #1<<5			@ check Thumb mode
+	subeq	lr, #4				@ next ARM instr
+	subne	lr, #6				@ next Thumb instr
+	movs	pc, lr
+do_abort_\@:
+	.endm
+
 	.macro get_irq_stack			@ setup IRQ stack
 	ldr	sp, IRQ_STACK_START
 	.endm
@@ -122,6 +137,7 @@ prefetch_abort:
 
 	.align	5
 data_abort:
+	try_data_abort
 	get_bad_stack
 	bad_save_user_regs
 	bl 	do_data_abort
@@ -202,5 +218,11 @@ _fiq: .word fiq
 
 .section .data
 .align 4
+.global arm_ignore_data_abort
+arm_ignore_data_abort:
+.word arm_ignore_data_abort /* When != 0 data aborts are ignored */
+.global arm_data_abort_occurred
+arm_data_abort_occurred:
+.word arm_data_abort_occurred /* set != 0 by the data abort handler */
 abort_stack:
 .space 8

arch/arm/cpu/interrupts.c

@@ -23,6 +23,7 @@
  */
 
 #include <common.h>
+#include <abort.h>
 #include <asm/ptrace.h>
 #include <asm/unwind.h>
 
@@ -161,3 +162,19 @@ void do_irq (struct pt_regs *pt_regs)
 	printf ("interrupt request\n");
 	do_exception(pt_regs);
 }
+
+extern volatile int arm_ignore_data_abort;
+extern volatile int arm_data_abort_occurred;
+
+void data_abort_mask(void)
+{
+	arm_data_abort_occurred = 0;
+	arm_ignore_data_abort = 1;
+}
+
+int data_abort_unmask(void)
+{
+	arm_ignore_data_abort = 0;
+
+	return arm_data_abort_occurred != 0;
+}

arch/arm/include/asm/barebox.h

@@ -5,4 +5,8 @@
 #define ARCH_HAS_STACK_DUMP
 #endif
 
+#ifdef CONFIG_ARM_EXCEPTIONS
+#define ARCH_HAS_DATA_ABORT_MASK
+#endif
+
 #endif	/* _BAREBOX_H_ */

include/abort.h

@@ -0,0 +1,37 @@
+#ifndef __ABORT_H
+#define __ABORT_H
+
+#include <asm/barebox.h>
+
+#ifdef ARCH_HAS_DATA_ABORT_MASK
+
+/*
+ * data_abort_mask - ignore data aborts
+ *
+ * If data aborts are ignored the data abort handler
+ * will just return.
+ */
+void data_abort_mask(void);
+
+/*
+ * data_abort_unmask - Enable data aborts
+ *
+ * returns true if a data abort has happened between calling data_abort_mask()
+ * and data_abort_unmask()
+ */
+int data_abort_unmask(void);
+
+#else
+
+static inline void data_abort_mask(void)
+{
+}
+
+static inline int data_abort_unmask(void)
+{
+	return 0;
+}
+
+#endif
+
+#endif /* __ABORT_H */