execute1: Make CFAR able to be written using mtspr and read using DMI debug

mtspr to CFAR is currently a no-op, which is not what should happen.
Make it set the contents of CFAR.

Also provide access to CFAR via the DMI debug interface as register 0x31.

Fixes: c2da82764f ("core: Implement CFAR register", 2020-06-15)
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

core_debug.vhdl

@@ -333,6 +333,9 @@ begin
                 when 5x"10" =>
                     isram := '0';
                     sel := SPRSEL_HEIR;
+                when 5x"11" =>
+                    isram := '0';
+                    sel := SPRSEL_CFAR;
                 when others =>
                     valid := '0';
             end case;

execute1.vhdl

@@ -79,6 +79,7 @@ architecture behaviour of execute1 is
         write_xerlow : std_ulogic;
         write_dec : std_ulogic;
         write_cfar : std_ulogic;
+        set_cfar : std_ulogic;
         write_loga : std_ulogic;
         inc_loga : std_ulogic;
         write_pmuspr : std_ulogic;
@@ -687,6 +688,8 @@ begin
                                 dbg_spr_data <= assemble_hfscr(ctrl);
                             when SPRSEL_HEIR =>
                                 dbg_spr_data <= ctrl.heir;
+                            when SPRSEL_CFAR =>
+                                dbg_spr_data <= ctrl.cfar;
                             when others =>
                                 dbg_spr_data <= assemble_xer(xerc_in, ctrl.xer_low);
                         end case;
@@ -1177,7 +1180,7 @@ begin
                 if ex1.msr(MSR_BE) = '1' then
                     v.do_trace := '1';
                 end if;
-                v.se.write_cfar := '1';
+                v.se.set_cfar := '1';
             when OP_BC =>
                 -- If CTR is being decremented, it is in ramspr_odd.
 		bo := insn_bo(e_in.insn);
@@ -1196,7 +1199,7 @@ begin
                 if ex1.msr(MSR_BE) = '1' then
                     v.do_trace := '1';
                 end if;
-                v.se.write_cfar := v.take_branch;
+                v.se.set_cfar := v.take_branch;
             when OP_BCREG =>
                 -- If CTR is being decremented, it is in ramspr_odd.
                 -- The target address is in ramspr_result (LR, CTR or TAR).
@@ -1209,7 +1212,7 @@ begin
                 if ex1.msr(MSR_BE) = '1' then
                     v.do_trace := '1';
                 end if;
-                v.se.write_cfar := v.take_branch;
+                v.se.set_cfar := v.take_branch;
 
 	    when OP_RFID =>
                 srr1 := ramspr_odd;
@@ -1229,7 +1232,7 @@ begin
                 end if;
                 v.se.write_msr := '1';
                 v.e.redirect := '1';
-                v.se.write_cfar := '1';
+                v.se.set_cfar := '1';
                 if HAS_FPU then
                     v.fp_intr := fp_in.exception and
                                  (srr1(MSR_FE0) or srr1(MSR_FE1));
@@ -1323,6 +1326,8 @@ begin
                             v.se.write_dec := '1';
                         when SPRSEL_LOGA =>
                             v.se.write_loga := '1';
+                        when SPRSEL_CFAR =>
+                            v.se.write_cfar := '1';
                         when SPRSEL_FSCR =>
                             v.se.write_fscr := '1';
                         when SPRSEL_HFSCR =>
@@ -1902,6 +1907,8 @@ begin
                 ctrl_tmp.dec <= ex1.e.write_data;
             end if;
             if ex1.se.write_cfar = '1' then
+                ctrl_tmp.cfar <= ex1.e.write_data;
+            elsif ex1.se.set_cfar = '1' then
                 ctrl_tmp.cfar <= ex1.e.last_nia;
             end if;
             if ex1.se.write_loga = '1' then

scripts/mw_debug/mw_debug.c

@@ -550,7 +550,7 @@ static const char *fast_spr_names[] =
 	"lr", "ctr", "srr0", "srr1", "hsrr0", "hsrr1",
 	"sprg0", "sprg1", "sprg2", "sprg3",
 	"hsprg0", "hsprg1", "xer", "tar",
-	"fscr", "hfscr", "heir",
+	"fscr", "hfscr", "heir", "cfar",
 };
 
 static const char *ldst_spr_names[] = {