[PATCH] ARM: give more detailed information about data aborts

[Enrico Scholz]

It is often very useful to get more details about a data abort.  Patch
decodes the "Data Fault Status Register" (DFSR) and because this
enlarges barebox a little bit, a Kconfig option was added to disable
this feature on demand.

Signed-off-by: Enrico Scholz <enrico.scholz at sigma-chemnitz.de>
---
 arch/arm/cpu/interrupts.c | 57 +++++++++++++++++++++++++++++++++++++++++------
 common/Kconfig            |  6 +++++
 2 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/arch/arm/cpu/interrupts.c b/arch/arm/cpu/interrupts.c
index 6e60adc..476ed3c 100644
--- a/arch/arm/cpu/interrupts.c
+++ b/arch/arm/cpu/interrupts.c
@@ -119,6 +119,43 @@ void do_prefetch_abort (struct pt_regs *pt_regs)
 	do_exception(pt_regs);
 }
 
+static char const *fault_status_str(u32 dfsr)
+{
+	static char		buf[sizeof("fault 0x12345")];
+	char const * const	REASONS[32] = {
+		[0x01] = "alignment fault",
+		[0x04] = "instruction cache maintenance fault",
+		[0x0a] = "translation table walk synchronous external abort (1st lvl)",
+		[0x0c] = "translation table walk synchronous external abort (2st lvl)",
+		[0x0a] = "translation table walk synchronous parity error (1st lvl)",
+		[0x0c] = "translation table walk synchronous parity error (2st lvl)",
+		[0x05] = "translation fault (section)",
+		[0x07] = "translation fault (page)",
+		[0x03] = "access flag fault (section)",
+		[0x06] = "access flag fault (page)",
+		[0x09] = "domain fault (section)",
+		[0x0b] = "domain fault (page)",
+		[0x0d] = "permission fault (section)",
+		[0x0f] = "permission fault (page)",
+		[0x02] = "debug event",
+		[0x10] = "synchronous external abort",
+		[0x19] = "memory access synchrounous parity error",
+		[0x16] = "asynchronous external abort",
+		[0x18] = "memory access asynchronous parity error",
+	};
+	char const		*res;
+	unsigned int		code = (((dfsr &   (1 << 10)) >> 6) |
+					((dfsr & (0xf <<  0)) >> 0));
+
+	res = REASONS[code];
+	if (res == NULL) {
+		snprintf(buf, sizeof buf, "fault 0x%05x", code);
+		res = buf;
+	}
+
+	return res;
+}
+
 /**
  * The CPU catches a data abort. That really should not happen!
  * @param[in] pt_regs Register set content when the accident happens
@@ -127,13 +164,19 @@ void do_prefetch_abort (struct pt_regs *pt_regs)
  */
 void do_data_abort (struct pt_regs *pt_regs)
 {
-	u32 far;
-
-	asm volatile ("mrc     p15, 0, %0, c6, c0, 0" : "=r" (far) : : "cc");
-
-	printf("unable to handle %s at address 0x%08x\n",
-			far < PAGE_SIZE ? "NULL pointer dereference" :
-			"paging request", far);
+	if (!IS_ENABLED(CONFIG_VERBOSE_EXCEPTIONS)) {
+		printf("data abort\n");
+	} else {
+		u32 far;
+		u32 dfsr;
+
+		asm volatile (
+			"mrc     p15, 0, %0, c6, c0, 0\n"
+			"mrc	 p15, 0, %1, c5, c0, 0\n"
+			: "=r" (far), "=r" (dfsr) : : "cc");
+
+		printf("%s at address 0x%08x\n", fault_status_str(dfsr), far);
+	}
 
 	do_exception(pt_regs);
 }
diff --git a/common/Kconfig b/common/Kconfig
index d60db80..d4c7154 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -668,6 +668,12 @@ config DEBUG_LL
 	help
 	  Enable this to get low level debug messages during barebox initialization.
 
+config VERBOSE_EXCEPTIONS
+	bool "decode processor specific exceptions"
+	default y
+	help
+	  Enable this to give out more detailed information about data aborts.
+
 endmenu
 
 config HAS_DEBUG_LL
-- 
1.7.11.7