[U-Boot] [PATCH v4] MIPS: Hang if run on a secondary CPU

[Paul Burton]

Some systems are configured such that multiple CPUs begin running from
their reset vector following a system reset. If this occurs then U-Boot
will be run on multiple CPUs simultaneously, which causes all sorts of
issues as the multiple instances of U-Boot clobber each other.

Prevent this from happening by simply hanging with an infinite loop if
we run on a CPU whose ID, as determined by GlobalNumber or EBase.CPUNum
as appropriate, is non-zero.

Signed-off-by: Paul Burton <paul.burton at imgtec.com>

---

Changes in v4:
- Presume Config5 is present for MIPSr6, as the arch says it will be

Changes in v3:
- Fix branch target for MIPSr6 case... Oops!

Changes in v2:
- Rebase atop u-boot-mips/next
- Execute a wait instruction in the loop
- Fill delay slots with NOPs

 arch/mips/cpu/start.S            | 21 ++++++++++++++++++++-
 arch/mips/include/asm/mipsregs.h |  7 +++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/mips/cpu/start.S b/arch/mips/cpu/start.S
index 8f85ede..5eca829 100644
--- a/arch/mips/cpu/start.S
+++ b/arch/mips/cpu/start.S
@@ -108,9 +108,28 @@ ENTRY(_start)
 
 	.align 4
 reset:
+#if __mips_isa_rev >= 6
+	mfc0	t0, CP0_CONFIG, 5
+	and	t0, t0, MIPS_CONF5_VP
+	beqz	t0, 1f
+	 nop
+
+	b	2f
+	 mfc0	t0, CP0_GLOBALNUMBER
+#endif
+
+1:	mfc0	t0, CP0_EBASE
+	and	t0, t0, EBASE_CPUNUM
+
+	/* Hang if this isn't the first CPU in the system */
+2:	beqz	t0, 4f
+	 nop
+3:	wait
+	b	3b
+	 nop
 
 	/* Clear watch registers */
-	MTC0	zero, CP0_WATCHLO
+4:	MTC0	zero, CP0_WATCHLO
 	mtc0	zero, CP0_WATCHHI
 
 	/* WP(Watch Pending), SW0/1 should be cleared */
diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index b4c2dff..9ab5063 100644
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -39,6 +39,7 @@
 #define CP0_ENTRYLO0 $2
 #define CP0_ENTRYLO1 $3
 #define CP0_CONF $3
+#define CP0_GLOBALNUMBER $3, 1
 #define CP0_CONTEXT $4
 #define CP0_PAGEMASK $5
 #define CP0_WIRED $6
@@ -361,6 +362,11 @@
 #define CAUSEF_BD		(_ULCAST_(1)   << 31)
 
 /*
+ * Bits in the coprocessor 0 EBase register.
+ */
+#define EBASE_CPUNUM		0x3ff
+
+/*
  * Bits in the coprocessor 0 config register.
  */
 /* Generic bits.  */
@@ -553,6 +559,7 @@
 #define MIPS_CONF5_MRP		(_ULCAST_(1) << 3)
 #define MIPS_CONF5_LLB		(_ULCAST_(1) << 4)
 #define MIPS_CONF5_MVH		(_ULCAST_(1) << 5)
+#define MIPS_CONF5_VP		(_ULCAST_(1) << 7)
 #define MIPS_CONF5_FRE		(_ULCAST_(1) << 8)
 #define MIPS_CONF5_UFE		(_ULCAST_(1) << 9)
 #define MIPS_CONF5_L2C		(_ULCAST_(1) << 10)
-- 
2.10.0