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dcache: Use discrete req_op_* signals instead of an encoded req_op

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Hopefully this will improve timing by reducing unnecessary
dependencies and giving more opportunities for routing.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This commit is contained in:
Paul Mackerras
2024-12-30 13:01:08 +11:00
parent ba4614c5f4
commit 0fbeaa2a01
1 changed files with 85 additions and 121 deletions
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206
dcache.vhdl
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@@ -181,16 +181,6 @@ architecture rtl of dcache is
constant real_mode_perm_attr : perm_attr_t := (nocache => '0', others => '1');
-- Type of operation on a "valid" input
type op_t is (OP_NONE,
OP_BAD, -- NC cache hit, TLB miss, prot/RC failure
OP_LOAD_HIT, -- Cache hit on load
OP_LOAD_MISS, -- Load missing cache
OP_LOAD_NC, -- Non-cachable load
OP_STORE, -- Store, whether hitting or missing cache
OP_NOP, -- nothing to do, just complete the op
OP_MISC); -- Flush
-- Cache state machine
type state_t is (IDLE, -- Normal load hit processing
RELOAD_WAIT_ACK, -- Cache reload wait ack
@@ -231,8 +221,9 @@ architecture rtl of dcache is
-- Clock edge between cycle 1 and cycle 2:
-- Request is stored in r1 (assuming r1.full was 0)
-- The state machine transitions out of IDLE state for a load miss,
-- a store, a dcbz, or a non-cacheable load. r1.full is set to 1
-- for a load miss, dcbz or non-cacheable load but not a store.
-- a store, a dcbz, a flush (dcbf) or a non-cacheable load.
-- r1.full is set to 1 for a load miss, dcbz, flush or
-- non-cacheable load but not a store.
--
-- Cycle 2: Completion signals are asserted for a load hit,
-- a store (excluding dcbz), a TLB operation, a conditional
@@ -288,7 +279,10 @@ architecture rtl of dcache is
signal r0_full : std_ulogic;
type mem_access_request_t is record
op : op_t;
op_lmiss : std_ulogic;
op_store : std_ulogic;
op_flush : std_ulogic;
nc : std_ulogic;
valid : std_ulogic;
dcbz : std_ulogic;
flush : std_ulogic;
@@ -380,14 +374,20 @@ architecture rtl of dcache is
signal kill_rsrv2 : std_ulogic;
-- Async signals on incoming request
signal req_index : index_t;
signal req_hit_way : way_t;
signal req_is_hit : std_ulogic;
signal req_tag : cache_tag_t;
signal req_op : op_t;
signal req_data : std_ulogic_vector(63 downto 0);
signal req_same_tag : std_ulogic;
signal req_go : std_ulogic;
signal req_index : index_t;
signal req_hit_way : way_t;
signal req_is_hit : std_ulogic;
signal req_tag : cache_tag_t;
signal req_op_load_hit : std_ulogic;
signal req_op_load_miss : std_ulogic;
signal req_op_store : std_ulogic;
signal req_op_flush : std_ulogic;
signal req_op_bad : std_ulogic;
signal req_op_nop : std_ulogic;
signal req_data : std_ulogic_vector(63 downto 0);
signal req_same_tag : std_ulogic;
signal req_go : std_ulogic;
signal req_nc : std_ulogic;
signal early_req_row : row_t;
signal early_rd_valid : std_ulogic;
@@ -912,8 +912,6 @@ begin
variable rindex : index_t;
variable is_hit : std_ulogic;
variable hit_way : way_t;
variable op : op_t;
variable opsel : std_ulogic_vector(2 downto 0);
variable go : std_ulogic;
variable nc : std_ulogic;
variable s_hit : std_ulogic;
@@ -1103,42 +1101,41 @@ begin
-- operation needs to be done
--
nc := r0.req.nc or perm_attr.nocache;
op := OP_NONE;
req_op_bad <= '0';
req_op_load_hit <= '0';
req_op_load_miss <= '0';
req_op_store <= '0';
req_op_nop <= '0';
req_op_flush <= '0';
if go = '1' then
if r0.req.touch = '1' then
if access_ok = '1' and is_hit = '0' and nc = '0' then
op := OP_LOAD_MISS;
req_op_load_miss <= '1';
elsif access_ok = '1' and is_hit = '1' and nc = '0' then
-- Make this OP_LOAD_HIT so the PLRU gets updated
op := OP_LOAD_HIT;
req_op_load_hit <= '1';
else
op := OP_NOP;
req_op_nop <= '1';
end if;
elsif access_ok = '0' then
op := OP_BAD;
req_op_bad <= '1';
elsif r0.req.flush = '1' then
if is_hit = '0' then
op := OP_NOP;
req_op_nop <= '1';
else
op := OP_MISC;
req_op_flush <= '1';
end if;
elsif nc = '1' and is_hit = '1' then
req_op_bad <= '1';
elsif r0.req.load = '0' then
req_op_store <= '1'; -- includes dcbz
else
opsel := r0.req.load & nc & is_hit;
case opsel is
when "101" => op := OP_LOAD_HIT;
when "100" => op := OP_LOAD_MISS;
when "110" => op := OP_LOAD_NC;
when "001" => op := OP_STORE;
when "000" => op := OP_STORE;
when "010" => op := OP_STORE;
when "011" => op := OP_BAD;
when "111" => op := OP_BAD;
when others => op := OP_NONE;
end case;
req_op_load_hit <= is_hit;
req_op_load_miss <= not is_hit; -- includes non-cacheable loads
end if;
end if;
req_op <= op;
req_go <= go;
req_nc <= nc;
-- Version of the row number that is valid one cycle earlier
-- in the cases where we need to read the cache data BRAM.
@@ -1309,14 +1306,6 @@ begin
variable data_out : std_ulogic_vector(63 downto 0);
begin
if rising_edge(clk) then
if req_op /= OP_NONE then
report "op:" & op_t'image(req_op) &
" addr:" & to_hstring(r0.req.addr) &
" nc:" & std_ulogic'image(r0.req.nc) &
" idx:" & to_hstring(req_index) &
" tag:" & to_hstring(req_tag) &
" way: " & to_hstring(req_hit_way);
end if;
if r0_valid = '1' then
r1.mmu_req <= r0.mmu_req;
end if;
@@ -1362,21 +1351,10 @@ begin
r1.forward_valid <= '1';
end if;
-- Fast path for load/store hits. Set signals for the writeback controls.
if req_op = OP_LOAD_HIT then
r1.hit_load_valid <= '1';
else
r1.hit_load_valid <= '0';
end if;
r1.hit_load_valid <= req_op_load_hit;
r1.cache_hit <= req_op_load_hit or (req_op_store and req_is_hit); -- causes PLRU update
-- The cache hit indication is used for PLRU updates
if req_op = OP_LOAD_HIT or req_op = OP_STORE then
r1.cache_hit <= req_is_hit;
else
r1.cache_hit <= '0';
end if;
if req_op = OP_BAD then
if req_op_bad = '1' then
report "Signalling ld/st error valid_ra=" & std_ulogic'image(valid_ra) &
" rc_ok=" & std_ulogic'image(rc_ok) & " perm_ok=" & std_ulogic'image(perm_ok);
r1.ls_error <= not r0.mmu_req;
@@ -1449,16 +1427,11 @@ begin
r1.write_bram <= '0';
r1.stcx_fail <= '0';
r1.ls_valid <= '0';
r1.ls_valid <= (req_op_load_hit or req_op_nop) and not r0.mmu_req;
-- complete tlbies and TLB loads in the third cycle
r1.mmu_done <= r0_valid and (r0.tlbie or r0.tlbld);
if req_op = OP_LOAD_HIT or req_op = OP_NOP then
if r0.mmu_req = '0' then
r1.ls_valid <= '1';
else
r1.mmu_done <= '1';
end if;
end if;
r1.mmu_done <= (r0_valid and (r0.tlbie or r0.tlbld)) or
(req_op_load_hit and r0.mmu_req);
-- The kill_rsrv2 term covers the case where the reservation
-- address was set at the beginning of this cycle, and a store
-- to that address happened in the previous cycle.
@@ -1499,11 +1472,14 @@ begin
end if;
-- Take request from r1.req if there is one there,
-- else from req_op, ra, etc.
-- else from req_op_*, ra, etc.
if r1.full = '1' then
req := r1.req;
else
req.op := req_op;
req.op_lmiss := req_op_load_miss;
req.op_store := req_op_store;
req.op_flush := req_op_flush;
req.nc := req_nc;
req.valid := req_go;
req.mmu_req := r0.mmu_req;
req.dcbz := r0.req.dcbz;
@@ -1532,9 +1508,8 @@ begin
req.same_tag := req_same_tag;
-- Store the incoming request from r0, if it is a slow request
-- Note that r1.full = 1 implies req_op = OP_NONE
if req_op = OP_LOAD_MISS or req_op = OP_LOAD_NC or
req_op = OP_STORE or req_op = OP_MISC then
-- Note that r1.full = 1 implies none of the req_op_* are 1
if req_op_load_miss = '1' or req_op_store = '1' or req_op_flush = '1' then
r1.req <= req;
r1.full <= '1';
end if;
@@ -1548,7 +1523,7 @@ begin
r1.victim_way <= plru_victim;
report "victim way:" & to_hstring(plru_victim);
end if;
if req_op = OP_LOAD_MISS or (r0.req.dcbz = '1' and req_is_hit = '0') then
if req_op_load_miss = '1' or (r0.req.dcbz = '1' and req_is_hit = '0') then
r1.choose_victim <= '1';
end if;
@@ -1584,46 +1559,43 @@ begin
r1.store_way <= req.hit_way;
end if;
-- Reset per-row valid bits, ready for handling OP_LOAD_MISS
-- Reset per-row valid bits, ready for handling the next load miss
for i in 0 to ROW_PER_LINE - 1 loop
r1.rows_valid(i) <= '0';
end loop;
case req.op is
when OP_LOAD_HIT =>
-- stay in IDLE state
when OP_LOAD_MISS =>
if req.op_lmiss = '1' then
-- Normal load cache miss, start the reload machine
--
report "cache miss real addr:" & to_hstring(req.real_addr) &
" idx:" & to_hstring(get_index(req.real_addr)) &
" tag:" & to_hstring(get_tag(req.real_addr));
-- Or non-cacheable load
if req.nc = '0' then
report "cache miss real addr:" & to_hstring(req.real_addr) &
" idx:" & to_hstring(get_index(req.real_addr)) &
" tag:" & to_hstring(get_tag(req.real_addr));
end if;
-- Start the wishbone cycle
r1.wb.we <= '0';
r1.wb.cyc <= '1';
r1.wb.stb <= '1';
-- Track that we had one request sent
r1.state <= RELOAD_WAIT_ACK;
r1.write_tag <= '1';
ev.load_miss <= '1';
if req.nc = '0' then
-- Track that we had one request sent
r1.state <= RELOAD_WAIT_ACK;
r1.write_tag <= '1';
ev.load_miss <= '1';
-- If this is a touch, complete the instruction
if req.touch = '1' then
r1.full <= '0';
r1.slow_valid <= '1';
r1.ls_valid <= '1';
-- If this is a touch, complete the instruction
if req.touch = '1' then
r1.full <= '0';
r1.slow_valid <= '1';
r1.ls_valid <= '1';
end if;
else
r1.state <= NC_LOAD_WAIT_ACK;
end if;
end if;
when OP_LOAD_NC =>
r1.wb.cyc <= '1';
r1.wb.stb <= '1';
r1.wb.we <= '0';
r1.state <= NC_LOAD_WAIT_ACK;
when OP_STORE =>
if req.op_store = '1' then
if req.reserve = '1' then
-- stcx needs to wait until next cycle
-- for the reservation address check
@@ -1650,20 +1622,12 @@ begin
r1.wb.cyc <= '1';
r1.wb.stb <= '1';
end if;
if req.op = OP_STORE then
ev.store_miss <= not req.is_hit;
end if;
ev.store_miss <= not req.is_hit;
end if;
when OP_MISC =>
if req.op_flush = '1' then
r1.state <= FLUSH_CYCLE;
-- OP_NONE and OP_BAD do nothing
-- OP_BAD & OP_NOP were handled above already
when OP_NONE =>
when OP_BAD =>
when OP_NOP =>
end case;
end if;
when RELOAD_WAIT_ACK =>
-- If we are still sending requests, was one accepted ?
@@ -1693,7 +1657,7 @@ begin
assert not is_X(r1.req.real_addr);
end if;
if r1.full = '1' and r1.req.same_tag = '1' and
((r1.dcbz = '1' and req.dcbz = '1') or r1.req.op = OP_LOAD_MISS) and
((r1.dcbz = '1' and req.dcbz = '1') or r1.req.op_lmiss = '1') and
r1.store_row = get_row(r1.req.real_addr) then
r1.full <= '0';
r1.slow_valid <= '1';
@@ -1745,7 +1709,7 @@ begin
end if;
assert not is_X(acks);
if acks < 7 and req.same_tag = '1' and req.dcbz = '0' and
req.op = OP_STORE then
req.op_store = '1' then
r1.wb.stb <= '1';
stbs_done := false;
r1.store_way <= req.hit_way;
@@ -1854,7 +1818,7 @@ begin
r1.wb.stb & r1.wb.cyc &
d_out.error &
d_out.valid &
std_ulogic_vector(to_unsigned(op_t'pos(req_op), 3)) &
req_op_load_miss & req_op_store & req_op_bad &
stall_out &
std_ulogic_vector(resize(tlb_hit_way, 3)) &
valid_ra &