Implement DSCR

The DSCR (Data Stream Control Register) is a user-accessible SPR that
controls aspects of data prefetching.  It has 25 bits of state defined
in the ISA.  This implements the register as a 25 read/write bits that
do nothing, since we don't have any prefetching.

The DSCR is accessible at two SPR numbers, 3 (unprivileged) and 17
(privileged).  Access via these SPR numbers is controlled by an FSCR
bit and an HFSCR bit.  The FSCR bit controls access via SPR 3 in user
mode.  The HFSCR bit controls access via SPR 3 in user mode and either
SPR number in privileged non-hypervisor mode, but since we don't
implement privileged non-hypervisor mode, it does essentially the same
thing as the FSCR bit.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

common.vhdl

@@ -60,6 +60,8 @@ package common is
     constant SPR_HEIR   : spr_num_t := 339;
     constant SPR_CTRL   : spr_num_t := 136;
     constant SPR_CTRLW  : spr_num_t := 152;
+    constant SPR_UDSCR  : spr_num_t := 3;
+    constant SPR_DSCR   : spr_num_t := 17;
 
     -- PMU registers
     constant SPR_UPMC1  : spr_num_t := 771;
@@ -166,13 +168,14 @@ package common is
     constant SPRSEL_HFSCR : spr_selector := 4x"8";
     constant SPRSEL_HEIR  : spr_selector := 4x"9";
     constant SPRSEL_CTRL  : spr_selector := 4x"a";
+    constant SPRSEL_DSCR  : spr_selector := 4x"b";
     constant SPRSEL_XER   : spr_selector := 4x"f";
 
     -- FSCR and HFSCR bit numbers
     constant FSCR_PREFIX   : integer := 63 - 50;
     constant FSCR_SCV      : integer := 63 - 51;
     constant FSCR_TAR      : integer := 63 - 55;
-    constant FSCR_DSCR3    : integer := 63 - 61;
+    constant FSCR_DSCR     : integer := 63 - 61;
     constant HFSCR_PREFIX  : integer := 63 - 50;
     constant HFSCR_MSG     : integer := 63 - 53;
     constant HFSCR_TAR     : integer := 63 - 55;
@@ -258,16 +261,20 @@ package common is
         fscr_ic: std_ulogic_vector(3 downto 0);
         fscr_pref: std_ulogic;
         fscr_tar: std_ulogic;
+        fscr_dscr: std_ulogic;
         hfscr_ic: std_ulogic_vector(3 downto 0);
         hfscr_pref: std_ulogic;
         hfscr_tar: std_ulogic;
+        hfscr_dscr: std_ulogic;
         hfscr_fp: std_ulogic;
         heir: std_ulogic_vector(63 downto 0);
+        dscr: std_ulogic_vector(24 downto 0);
     end record;
     constant ctrl_t_init : ctrl_t :=
         (wait_state => '0', run => '1', xer_low => 18x"0",
-         fscr_ic => x"0", fscr_pref => '1', fscr_tar => '1',
-         hfscr_ic => x"0", hfscr_pref => '1', hfscr_tar => '1', hfscr_fp => '1',
+         fscr_ic => x"0", fscr_pref => '1', fscr_tar => '1', fscr_dscr => '1',
+         hfscr_ic => x"0", hfscr_pref => '1', hfscr_tar => '1', hfscr_dscr => '1', hfscr_fp => '1',
+         dscr => (others => '0'),
          others => (others => '0'));
 
     type Fetch1ToIcacheType is record
@@ -415,6 +422,7 @@ package common is
         illegal_suffix : std_ulogic;
         misaligned_prefix : std_ulogic;
         uses_tar : std_ulogic;
+        uses_dscr : std_ulogic;
     end record;
     constant Decode2ToExecute1Init : Decode2ToExecute1Type :=
 	(valid => '0', unit => ALU, fac => NONE, insn_type => OP_ILLEGAL, instr_tag => instr_tag_init,
@@ -435,7 +443,7 @@ package common is
          dbg_spr_access => '0',
          dec_ctr => '0',
          prefixed => '0', prefix => (others => '0'), illegal_suffix => '0',
-         misaligned_prefix => '0', uses_tar => '0',
+         misaligned_prefix => '0', uses_tar => '0', uses_dscr => '0',
          others => (others => '0'));
 
     type MultiplyInputType is record

decode1.vhdl

@@ -466,6 +466,10 @@ architecture behaviour of decode1 is
             when SPR_CTRLW =>
                 i.sel := SPRSEL_CTRL;
                 i.wonly := '1';
+            when SPR_UDSCR =>
+                i.sel := SPRSEL_DSCR;
+            when SPR_DSCR =>
+                i.sel := SPRSEL_DSCR;
             when others =>
                 i.valid := '0';
         end case;

decode2.vhdl

@@ -454,6 +454,8 @@ begin
                                 unit := LDST;
                             when SPR_TAR =>
                                 v.e.uses_tar := '1';
+                            when SPR_UDSCR =>
+                                v.e.uses_dscr := '1';
                             when others =>
                         end case;
                         if d_in.spr_info.wonly = '1' then
@@ -477,6 +479,8 @@ begin
                                 end if;
                             when SPR_TAR =>
                                 v.e.uses_tar := '1';
+                            when SPR_UDSCR =>
+                                v.e.uses_dscr := '1';
                             when others =>
                         end case;
                         if d_in.spr_info.ronly = '1' then

execute1.vhdl

@@ -94,6 +94,7 @@ architecture behaviour of execute1 is
         write_heir : std_ulogic;
         set_heir : std_ulogic;
         write_ctrl : std_ulogic;
+        write_dscr : std_ulogic;
         enter_wait : std_ulogic;
     end record;
     constant side_effect_init : side_effect_type := (others => '0');
@@ -393,6 +394,7 @@ architecture behaviour of execute1 is
         ret(59 downto 56) := c.fscr_ic;
         ret(FSCR_PREFIX) := c.fscr_pref;
         ret(FSCR_TAR) := c.fscr_tar;
+        ret(FSCR_DSCR) := c.fscr_dscr;
         return ret;
     end;
 
@@ -403,6 +405,7 @@ architecture behaviour of execute1 is
         ret(59 downto 56) := c.hfscr_ic;
         ret(HFSCR_PREFIX) := c.hfscr_pref;
         ret(HFSCR_TAR) := c.hfscr_tar;
+        ret(HFSCR_DSCR) := c.hfscr_dscr;
         ret(HFSCR_FP) := c.hfscr_fp;
         return ret;
     end;
@@ -1348,6 +1351,8 @@ begin
                             v.se.write_heir := '1';
                         when SPRSEL_CTRL =>
                             v.se.write_ctrl := '1';
+                        when SPRSEL_DSCR =>
+                            v.se.write_dscr := '1';
                         when others =>
                     end case;
                 end if;
@@ -1480,6 +1485,20 @@ begin
                 v.se.write_ic := '1';
             end if;
 
+        elsif ex1.msr(MSR_PR) = '1' and e_in.uses_dscr = '1' and
+            (ctrl.hfscr_dscr = '0' or ctrl.fscr_dscr = '0') then
+            -- [Hypervisor] facility unavailable for DSCR access
+            v.exception := '1';
+            v.ic := x"2";
+            if ctrl.hfscr_dscr = '0' then
+                v.e.hv_intr := '1';
+                v.e.intr_vec := 16#f80#;
+                v.se.write_hic := '1';
+            else
+                v.e.intr_vec := 16#f60#;
+                v.se.write_ic := '1';
+            end if;
+
         elsif HAS_FPU and ex1.msr(MSR_PR) = '1' and e_in.fac = FPU and
             ctrl.hfscr_fp = '0' then
             -- Hypervisor facility unavailable for FP instructions
@@ -1793,6 +1812,7 @@ begin
         assemble_hfscr(ctrl) when SPRSEL_HFSCR,
         ctrl.heir when SPRSEL_HEIR,
         assemble_ctrl(ctrl, ex1.msr(MSR_PR)) when SPRSEL_CTRL,
+        39x"0" & ctrl.dscr when SPRSEL_DSCR,
         assemble_xer(ex1.e.xerc, ctrl.xer_low) when others;
 
     stage2_stall <= l_in.l2stall or fp_in.f2stall;
@@ -1942,6 +1962,7 @@ begin
                 ctrl_tmp.hfscr_ic <= ex1.e.write_data(59 downto 56);
                 ctrl_tmp.hfscr_pref <= ex1.e.write_data(HFSCR_PREFIX);
                 ctrl_tmp.hfscr_tar <= ex1.e.write_data(HFSCR_TAR);
+                ctrl_tmp.hfscr_dscr <= ex1.e.write_data(HFSCR_DSCR);
                 ctrl_tmp.hfscr_fp <= ex1.e.write_data(HFSCR_FP);
             elsif ex1.se.write_hic = '1' then
                 ctrl_tmp.hfscr_ic <= ex1.ic;
@@ -1950,6 +1971,7 @@ begin
                 ctrl_tmp.fscr_ic <= ex1.e.write_data(59 downto 56);
                 ctrl_tmp.fscr_pref <= ex1.e.write_data(FSCR_PREFIX);
                 ctrl_tmp.fscr_tar <= ex1.e.write_data(FSCR_TAR);
+                ctrl_tmp.fscr_dscr <= ex1.e.write_data(FSCR_DSCR);
             elsif ex1.se.write_ic = '1' then
                 ctrl_tmp.fscr_ic <= ex1.ic;
             end if;
@@ -1967,6 +1989,9 @@ begin
             if ex1.se.write_ctrl = '1' then
                 ctrl_tmp.run <= ex1.e.write_data(0);
             end if;
+            if ex1.se.write_dscr = '1' then
+                ctrl_tmp.dscr <= ex1.e.write_data(24 downto 0);
+            end if;
             if ex1.se.enter_wait = '1' then
                 ctrl_tmp.wait_state <= '1';
             end if;