insn: Implement isync instruction

The instruction works by redirecting fetch to nia+4 (hopefully using
the same adder used to generate LR) and doing a backflush. Along with
being single issue, this should guarantee that the next instruction
only gets fetched after the pipe's been emptied.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

decode1.vhdl

@@ -108,7 +108,7 @@ architecture behaviour of decode1 is
                 -- bclr, bcctr, bctar
 		2#100#    =>       (ALU,    OP_BCREG,     NONE,       NONE,        NONE, NONE, '1', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '1', '1'),
                 -- isync
-		2#111#    =>       (ALU,    OP_NOP,       NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'),
+		2#111#    =>       (ALU,    OP_ISYNC,     NONE,       NONE,        NONE, NONE, '0', '0', '0', '0', ZERO, '0', NONE, '0', '0', '0', '0', '0', '0', NONE, '0', '1'),
 		others   => illegal_inst
         );
 

execute1.vhdl

@@ -118,6 +118,7 @@ begin
 	variable bo, bi : std_ulogic_vector(4 downto 0);
 	variable bf, bfa : std_ulogic_vector(2 downto 0);
 	variable l : std_ulogic;
+	variable next_nia : std_ulogic_vector(63 downto 0);
     begin
 	result := (others => '0');
 	result_with_carry := (others => '0');
@@ -135,6 +136,9 @@ begin
 	terminate_out <= '0';
 	f_out <= Execute1ToFetch1TypeInit;
 
+	-- Next insn adder used in a couple of places
+	next_nia := std_ulogic_vector(unsigned(e_in.nia) + 4);
+
 	-- rotator control signals
 	right_shift <= '1' when e_in.insn_type = OP_SHR else '0';
 	rot_clear_left <= '1' when e_in.insn_type = OP_RLC or e_in.insn_type = OP_RLCL else '0';
@@ -345,13 +349,17 @@ begin
 		-- Keep our test cases happy for now, ignore trap instructions
 		report "OP_TDI FIXME";
 
+	    when OP_ISYNC =>
+		f_out.redirect <= '1';
+		f_out.redirect_nia <= next_nia;
+
 	    when others =>
 		terminate_out <= '1';
 		report "illegal";
 	    end case;
 
 	    if e_in.lr = '1' then
-		ctrl_tmp.lr <= std_ulogic_vector(unsigned(e_in.nia) + 4);
+		ctrl_tmp.lr <= next_nia;
 	    end if;
 
 	end if;