[hmac, rtl] Do not skip padding after a hash stop command

This commit removes some conditional FSM states transition that were deemed undesirable in `prim_sha2_pad`, see #23936. It made it possible to cancel an ongoing padding operation, which is disallowed by the HMAC module. As a side-effect, the removal plugs some existing FSM transition coverage holes in `prim_sha2_pad` whose manual exclusions can be removed as well. This change makes it impossible to transition into the `StFifoReceive` state from either `StPad80`, `StPad00`, `StLenHi` or `StLenLo` by asserting the `hash_go` signal. Signed-off-by: Andrea Caforio <[email protected]>
lowRISC · Dec 11, 2024 · f2b230b · f2b230b
1 parent b70973d
commit f2b230b
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Showing 3 changed files with 8 additions and 29 deletions.
diff --git a/hw/ip/hmac/dv/cov/hmac_cov_excl.el b/hw/ip/hmac/dv/cov/hmac_cov_excl.el
diff --git a/hw/ip/hmac/dv/hmac_sim_cfg.hjson b/hw/ip/hmac/dv/hmac_sim_cfg.hjson
@@ -41,8 +41,7 @@
   reseed: 50
 
   // Add HMAC specific exclusion files.
-  vcs_cov_excl_files: ["{proj_root}/hw/ip/hmac/dv/cov/hmac_unr_excl.el",
-                       "{proj_root}/hw/ip/hmac/dv/cov/hmac_cov_excl.el"]
+  vcs_cov_excl_files: ["{proj_root}/hw/ip/hmac/dv/cov/hmac_unr_excl.el"]
 
   // Default UVM test and seq class name.
   uvm_test: hmac_base_test

diff --git a/hw/ip/prim/rtl/prim_sha2_pad.sv b/hw/ip/prim/rtl/prim_sha2_pad.sv
@@ -337,8 +337,13 @@ module prim_sha2_pad import prim_sha2_pkg::*;
       end
     endcase
 
-    if (!sha_en_i)    st_d = StIdle;
-    else if (hash_go) st_d = StFifoReceive;
+    if (!sha_en_i) begin
+      st_d = StIdle;
+    // We do not allow the cancellation of an ongoing padding operation, i.e., reverting back to the
+    // `StFifoReceive` state while being in the states `StPad80`, `StPad00`, `StLenHi` or `StLenLo`.
+    end else if (hash_go && (st_q == StIdle || st_q == StFifoReceive)) begin
+      st_d = StFifoReceive;
+    end
   end
 
   // tx_count