MIPS: microMIPS: Add support for exception handling.

All exceptions must be taken in microMIPS mode, never in classic
MIPS mode or the kernel falls apart. A few NOP instructions are
used to maintain the correct alignment of microMIPS versions of
the exception vectors.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/arch/mips/mti-sead3/sead3-init.c b/arch/mips/mti-sead3/sead3-init.c
index 562dccf56ee8..bfbd17b120a2 100644
--- a/arch/mips/mti-sead3/sead3-init.c
+++ b/arch/mips/mti-sead3/sead3-init.c
@@ -65,7 +65,41 @@ static void __init mips_nmi_setup(void)
 	base = cpu_has_veic ?
 		(void *)(CAC_BASE + 0xa80) :
 		(void *)(CAC_BASE + 0x380);
+#ifdef CONFIG_CPU_MICROMIPS
+	/*
+	 * Decrement the exception vector address by one for microMIPS.
+	 */
+	memcpy(base, (&except_vec_nmi - 1), 0x80);
+
+	/*
+	 * This is a hack. We do not know if the boot loader was built with
+	 * microMIPS instructions or not. If it was not, the NMI exception
+	 * code at 0x80000a80 will be taken in MIPS32 mode. The hand coded
+	 * assembly below forces us into microMIPS mode if we are a pure
+	 * microMIPS kernel. The assembly instructions are:
+	 *
+	 *  3C1A8000   lui       k0,0x8000
+	 *  375A0381   ori       k0,k0,0x381
+	 *  03400008   jr        k0
+	 *  00000000   nop
+	 *
+	 * The mode switch occurs by jumping to the unaligned exception
+	 * vector address at 0x80000381 which would have been 0x80000380
+	 * in MIPS32 mode. The jump to the unaligned address transitions
+	 * us into microMIPS mode.
+	 */
+	if (!cpu_has_veic) {
+		void *base2 = (void *)(CAC_BASE + 0xa80);
+		*((unsigned int *)base2) = 0x3c1a8000;
+		*((unsigned int *)base2 + 1) = 0x375a0381;
+		*((unsigned int *)base2 + 2) = 0x03400008;
+		*((unsigned int *)base2 + 3) = 0x00000000;
+		flush_icache_range((unsigned long)base2,
+			(unsigned long)base2 + 0x10);
+	}
+#else
 	memcpy(base, &except_vec_nmi, 0x80);
+#endif
 	flush_icache_range((unsigned long)base, (unsigned long)base + 0x80);
 }
 
@@ -76,7 +110,21 @@ static void __init mips_ejtag_setup(void)
 	base = cpu_has_veic ?
 		(void *)(CAC_BASE + 0xa00) :
 		(void *)(CAC_BASE + 0x300);
+#ifdef CONFIG_CPU_MICROMIPS
+	/* Deja vu... */
+	memcpy(base, (&except_vec_ejtag_debug - 1), 0x80);
+	if (!cpu_has_veic) {
+		void *base2 = (void *)(CAC_BASE + 0xa00);
+		*((unsigned int *)base2) = 0x3c1a8000;
+		*((unsigned int *)base2 + 1) = 0x375a0301;
+		*((unsigned int *)base2 + 2) = 0x03400008;
+		*((unsigned int *)base2 + 3) = 0x00000000;
+		flush_icache_range((unsigned long)base2,
+			(unsigned long)base2 + 0x10);
+	}
+#else
 	memcpy(base, &except_vec_ejtag_debug, 0x80);
+#endif
 	flush_icache_range((unsigned long)base, (unsigned long)base + 0x80);
 }