MIPS: MIPS16e: Support handling of delay slots.

Add logic needed to properly calculate exceptions for delay slots
when in MIPS16e mode.
Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>

arch/mips/include/asm/branch.h

@@ -16,6 +16,7 @@ extern int __compute_return_epc(struct pt_regs *regs);
 extern int __compute_return_epc_for_insn(struct pt_regs *regs,
 					 union mips_instruction insn);
 extern int __microMIPS_compute_return_epc(struct pt_regs *regs);
+extern int __MIPS16e_compute_return_epc(struct pt_regs *regs);
 
 
 static inline int delay_slot(struct pt_regs *regs)
@@ -41,6 +42,8 @@ static inline int compute_return_epc(struct pt_regs *regs)
 	if (get_isa16_mode(regs->cp0_epc)) {
 		if (cpu_has_mmips)
 			return __microMIPS_compute_return_epc(regs);
+		if (cpu_has_mips16)
+			return __MIPS16e_compute_return_epc(regs);
 		return regs->cp0_epc;
 	}
 
@@ -52,4 +55,19 @@ static inline int compute_return_epc(struct pt_regs *regs)
 	return __compute_return_epc(regs);
 }
 
+static inline int MIPS16e_compute_return_epc(struct pt_regs *regs,
+					     union mips16e_instruction *inst)
+{
+	if (likely(!delay_slot(regs))) {
+		if (inst->ri.opcode == MIPS16e_extend_op) {
+			regs->cp0_epc += 4;
+			return 0;
+		}
+		regs->cp0_epc += 2;
+		return 0;
+	}
+
+	return __MIPS16e_compute_return_epc(regs);
+}
+
 #endif /* _ASM_BRANCH_H */

arch/mips/include/asm/inst.h

@@ -82,4 +82,7 @@ struct mm_decoded_insn {
 	int micro_mips_mode;
 };
 
+/* Recode table from 16-bit register notation to 32-bit GPR. Do NOT export!!! */
+extern const int reg16to32[];
+
 #endif /* _ASM_INST_H */

arch/mips/kernel/branch.c

@@ -20,13 +20,13 @@
 #include <asm/uaccess.h>
 
 /*
- * Calculate and return exception PC in case of branch delay
- * slot for microMIPS. It does not clear the ISA mode bit.
+ * Calculate and return exception PC in case of branch delay slot
+ * for microMIPS and MIPS16e. It does not clear the ISA mode bit.
  */
 int __isa_exception_epc(struct pt_regs *regs)
 {
-	long epc = regs->cp0_epc;
 	unsigned short inst;
+	long epc = regs->cp0_epc;
 
 	/* Calculate exception PC in branch delay slot. */
 	if (__get_user(inst, (u16 __user *) msk_isa16_mode(epc))) {
@@ -34,8 +34,13 @@ int __isa_exception_epc(struct pt_regs *regs)
 		force_sig(SIGSEGV, current);
 		return epc;
 	}
-
-	if (mm_insn_16bit(inst))
+	if (cpu_has_mips16) {
+		if (((union mips16e_instruction)inst).ri.opcode
+				== MIPS16e_jal_op)
+			epc += 4;
+		else
+			epc += 2;
+	} else if (mm_insn_16bit(inst))
 		epc += 2;
 	else
 		epc += 4;
@@ -101,6 +106,94 @@ int __microMIPS_compute_return_epc(struct pt_regs *regs)
 	return -EFAULT;
 }
 
+/*
+ * Compute return address and emulate branch in MIPS16e mode after an
+ * exception only. It does not handle compact branches/jumps and cannot
+ * be used in interrupt context. (Compact branches/jumps do not cause
+ * exceptions.)
+ */
+int __MIPS16e_compute_return_epc(struct pt_regs *regs)
+{
+	u16 __user *addr;
+	union mips16e_instruction inst;
+	u16 inst2;
+	u32 fullinst;
+	long epc;
+
+	epc = regs->cp0_epc;
+
+	/* Read the instruction. */
+	addr = (u16 __user *)msk_isa16_mode(epc);
+	if (__get_user(inst.full, addr)) {
+		force_sig(SIGSEGV, current);
+		return -EFAULT;
+	}
+
+	switch (inst.ri.opcode) {
+	case MIPS16e_extend_op:
+		regs->cp0_epc += 4;
+		return 0;
+
+		/*
+		 *  JAL and JALX in MIPS16e mode
+		 */
+	case MIPS16e_jal_op:
+		addr += 1;
+		if (__get_user(inst2, addr)) {
+			force_sig(SIGSEGV, current);
+			return -EFAULT;
+		}
+		fullinst = ((unsigned)inst.full << 16) | inst2;
+		regs->regs[31] = epc + 6;
+		epc += 4;
+		epc >>= 28;
+		epc <<= 28;
+		/*
+		 * JAL:5 X:1 TARGET[20-16]:5 TARGET[25:21]:5 TARGET[15:0]:16
+		 *
+		 * ......TARGET[15:0].................TARGET[20:16]...........
+		 * ......TARGET[25:21]
+		 */
+		epc |=
+		    ((fullinst & 0xffff) << 2) | ((fullinst & 0x3e00000) >> 3) |
+		    ((fullinst & 0x1f0000) << 7);
+		if (!inst.jal.x)
+			set_isa16_mode(epc);	/* Set ISA mode bit. */
+		regs->cp0_epc = epc;
+		return 0;
+
+		/*
+		 *  J(AL)R(C)
+		 */
+	case MIPS16e_rr_op:
+		if (inst.rr.func == MIPS16e_jr_func) {
+
+			if (inst.rr.ra)
+				regs->cp0_epc = regs->regs[31];
+			else
+				regs->cp0_epc =
+				    regs->regs[reg16to32[inst.rr.rx]];
+
+			if (inst.rr.l) {
+				if (inst.rr.nd)
+					regs->regs[31] = epc + 2;
+				else
+					regs->regs[31] = epc + 4;
+			}
+			return 0;
+		}
+		break;
+	}
+
+	/*
+	 * All other cases have no branch delay slot and are 16-bits.
+	 * Branches do not cause an exception.
+	 */
+	regs->cp0_epc += 2;
+
+	return 0;
+}
+
 /**
  * __compute_return_epc_for_insn - Computes the return address and do emulate
  *				    branch simulation, if required.