[PATCH v2] MIPS: Make check condition for SDBBP consistent with EJTAG spec

[Tiezhu Yang]

According to MIPS EJTAG Specification [1], a Debug Breakpoint
exception occurs when an SDBBP instruction is executed, the
CP0_DEBUG bit DBp indicates that a Debug Breakpoint exception
occurred, just check bit DBp for SDBBP is more accurate.

[1] http://www.t-es-t.hu/download/mips/md00047f.pdf

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---

v2: add MIPS_DEBUG_DBP definition

 arch/mips/include/asm/mipsregs.h | 4 ++++
 arch/mips/kernel/genex.S         | 4 ++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index a0e8ae5..9c8099a 100644
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -1085,6 +1085,10 @@
 #define CVMVMCONF_RMMUSIZEM1_S	0
 #define CVMVMCONF_RMMUSIZEM1	(_U64CAST_(0xff) << CVMVMCONF_RMMUSIZEM1_S)
 
+/* Debug register field definitions */
+#define MIPS_DEBUG_DBP_SHIFT	1
+#define MIPS_DEBUG_DBP		(_ULCAST_(1) << MIPS_DEBUG_DBP_SHIFT)
+
 /*
  * Coprocessor 1 (FPU) register names
  */
diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index bcce32a..743d759 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -349,8 +349,8 @@ NESTED(ejtag_debug_handler, PT_SIZE, sp)
 	MTC0	k0, CP0_DESAVE
 	mfc0	k0, CP0_DEBUG
 
-	sll	k0, k0, 30	# Check for SDBBP.
-	bgez	k0, ejtag_return
+	andi	k0, k0, MIPS_DEBUG_DBP	# Check for SDBBP.
+	beqz	k0, ejtag_return
 
 #ifdef CONFIG_SMP
 1:	PTR_LA	k0, ejtag_debug_buffer_spinlock
-- 
2.1.0