[keymgr] Don't update and reseed PRNG in Disabled/Invalid state forever

hw/ip/keymgr/rtl/keymgr.sv

@@ -185,6 +185,7 @@ module keymgr
   logic [LfsrWidth-1:0] seed;
   logic reseed_req;
   logic reseed_ack;
+  logic reseed_done;
   logic reseed_cnt_err;
 
   keymgr_reseed_ctrl u_reseed_ctrl (
@@ -194,6 +195,7 @@ module keymgr
     .rst_edn_ni,
     .reseed_req_i(reseed_req),
     .reseed_ack_o(reseed_ack),
+    .reseed_done_o(reseed_done),
     .reseed_interval_i(reg2hw.reseed_interval_shadowed.q),
     .edn_o,
     .edn_i,
@@ -285,6 +287,7 @@ module keymgr
     .sideload_fsm_err_i(sideload_fsm_err),
     .prng_reseed_req_o(reseed_req),
     .prng_reseed_ack_i(reseed_ack),
+    .prng_reseed_done_i(reseed_done),
     .prng_en_o(ctrl_lfsr_en),
     .entropy_i(ctrl_rand),
     .op_i(keymgr_ops_e'(reg2hw.control_shadowed.operation.q)),

hw/ip/keymgr/rtl/keymgr_ctrl.sv

@@ -66,6 +66,7 @@ module keymgr_ctrl
 
   // prng control interface
   input [Shares-1:0][RandWidth-1:0] entropy_i,
+  input prng_reseed_done_i,
   input prng_reseed_ack_i,
   output logic prng_reseed_req_o,
   output logic prng_en_o
@@ -234,7 +235,24 @@ module keymgr_ctrl
   //  interaction between main fsm and prng
   ///////////////////////////
 
-  assign prng_en_o = random_req | disabled | invalid | wipe_req;
+  // Upon entering StCtrlDisabled or StCtrlInvalid, the PRNG is kept advancing until it has been
+  // reseeded twice (through the reseeding mechansism inside keymgr_reseed_ctrl.sv).
+  logic [1:0] prng_en_dis_inv_d, prng_en_dis_inv_q;
+  logic prng_en_dis_inv_set;
+
+  assign prng_en_dis_inv_d =
+      prng_en_dis_inv_set ? 2'b11 :
+      prng_reseed_done_i  ? {1'b0, prng_en_dis_inv_q[1]} : prng_en_dis_inv_q;
+
+  always_ff @(posedge clk_i or negedge rst_ni) begin
+    if (!rst_ni) begin
+      prng_en_dis_inv_q <= '0;
+    end else begin
+      prng_en_dis_inv_q <= prng_en_dis_inv_d;
+    end
+  end
+
+  assign prng_en_o = random_req | wipe_req | prng_en_dis_inv_q[0];
 
   //////////////////////////
   // Main Control FSM
@@ -456,7 +474,10 @@ module keymgr_ctrl
     // indication that state is invalid
     invalid = 1'b0;
 
-    // enable prng toggling
+    // Don't request final PRNG updating and reseeding.
+    prng_en_dis_inv_set = 1'b0;
+
+    // Request PRNG reseeding.
     prng_reseed_req_o = 1'b0;
 
     // initialization complete
@@ -535,6 +556,7 @@ module keymgr_ctrl
           state_d = StCtrlWipe;
         end else if (dis_state) begin
           state_d = StCtrlDisabled;
+          prng_en_dis_inv_set = 1'b1;
         end else if (adv_state) begin
           state_d = StCtrlCreatorRootKey;
         end
@@ -554,6 +576,7 @@ module keymgr_ctrl
           state_d = StCtrlWipe;
         end else if (dis_state) begin
           state_d = StCtrlDisabled;
+          prng_en_dis_inv_set = 1'b1;
         end else if (adv_state) begin
           state_d = StCtrlOwnerIntKey;
         end
@@ -573,6 +596,7 @@ module keymgr_ctrl
           state_d = StCtrlWipe;
         end else if (dis_state) begin
           state_d = StCtrlDisabled;
+          prng_en_dis_inv_set = 1'b1;
         end else if (adv_state) begin
           state_d = StCtrlOwnerKey;
         end
@@ -592,6 +616,7 @@ module keymgr_ctrl
           state_d = StCtrlWipe;
         end else if (adv_state || dis_state) begin
           state_d = StCtrlDisabled;
+          prng_en_dis_inv_set = 1'b1;
         end
       end
 
@@ -614,6 +639,7 @@ module keymgr_ctrl
         //    begin with (op_start_i == 0), in this case, don't wait and immediately transition
         if (!op_start_i) begin
           state_d = StCtrlInvalid;
+          prng_en_dis_inv_set = 1'b1;
         end
       end
 

hw/ip/keymgr/rtl/keymgr_reseed_ctrl.sv

@@ -16,6 +16,7 @@ module keymgr_reseed_ctrl import keymgr_pkg::*; (
   // interface to keymgr_ctrl
   input reseed_req_i,
   output logic reseed_ack_o,
+  output logic reseed_done_o,
 
   // interface to software
   input [15:0] reseed_interval_i,
@@ -57,6 +58,7 @@ module keymgr_reseed_ctrl import keymgr_pkg::*; (
 
   assign seed_en_o = edn_ack;
   assign reseed_ack_o = reseed_req_i & edn_ack;
+  assign reseed_done_o = edn_done;
 
   prim_edn_req #(
     .OutWidth(LfsrWidth)