[rtl] Fix Gift cipher lint errors

- Import::* may pollute global namespace
- Signal width is different
- Signal is not used
- Signal unoptimizable: Feedback to clock or circular logic

lint/verilator_waiver.vlt

@@ -162,3 +162,9 @@ lint_off -rule UNOPTFLAT -file "*/rtl/ibex_cs_registers.sv" -match "*ibex_core.c
 // Temporary waivers until OpenTitan primitives are lint-clean
 // https://github.com/lowRISC/opentitan/issues/2313
 lint_off -file "*/lowrisc_prim_*/rtl/*.sv"
+
+// Signal unoptimizable: Feedback to clock or circular logic:
+// We use 2D packed arrays to hold data and keys for multpile cipher iterations:
+// data_states[i][:] is used to generate data_states[i+1][:] but there is no cicular logic.
+lint_off -rule UNOPTFLAT -file "*/rtl/gift_middle_rounds.sv" -match "*ibex_core.g_pa.pointer_authentication_i.gift_i.gift_middle_rounds_i.data_states*"
+lint_off -rule UNOPTFLAT -file "*/rtl/gift_middle_rounds.sv" -match "*ibex_core.g_pa.pointer_authentication_i.gift_i.gift_middle_rounds_i.key_states*"

rtl/gift_middle_rounds.sv

@@ -2,8 +2,6 @@
 // Licensed under the Apache License, Version 2.0, see LICENSE for details.
 // SPDX-License-Identifier: Apache-2.0
 
-import gift_pkg::*;
-
 module gift_middle_rounds (
 
     // Data and key coming directly from the cipher input
@@ -14,12 +12,13 @@ module gift_middle_rounds (
     input logic [63:0]    state_data_i,
     input logic [127:0]   state_key_i,
 
-    input round_index_e    round_base_i,
+    input gift_pkg::round_index_e round_base_i,
 
     output logic [63:0]   data_o,
     output logic [127:0]  key_o
 );
 
+  import gift_pkg::*;
 
   // Internal signals
 

rtl/gift_round.sv

@@ -17,6 +17,10 @@ module gift_round (
   logic [63:0] data_after_permut;
   logic [63:0] data_after_key;
 
+  // Avoid lint warning
+  logic [63:0] unused_data_after_permut;
+  logic [63:0] unused_data_after_key;
+
   gift_update_key i_gift_update_key (
     .key_i(key_i),
     .key_o(key_o)
@@ -59,4 +63,8 @@ module gift_round (
 
   assign data_o = data_state;
 
+  // Avoid lint warning
+  assign unused_data_after_permut = data_after_permut;
+  assign unused_data_after_key    = data_after_key;
+
 endmodule