Revert wrongfully removed description. Changed encoding only

Signed-off-by: Afonso Oliveira <[email protected]>

arch/inst/Zifencei/fence.i.yaml

@@ -1,25 +1,43 @@
 # yaml-language-server: $schema=../../../schemas/inst_schema.json
 
 fence.i:
-  long_name: No synopsis available.
+  long_name: Instruction fence
   description: |
-      No description available.
+    The FENCE.I instruction is used to synchronize the instruction and data
+    streams. RISC-V does not guarantee that stores to instruction memory
+    will be made visible to instruction fetches on a RISC-V hart until that
+    hart executes a FENCE.I instruction. A FENCE.I instruction ensures that
+    a subsequent instruction fetch on a RISC-V hart will see any previous
+    data stores already visible to the same RISC-V hart. FENCE.I does _not_
+    ensure that other RISC-V harts' instruction fetches will observe the
+    local hart's stores in a multiprocessor system. To make a store to
+    instruction memory visible to all RISC-V harts, the writing hart also
+    has to execute a data FENCE before requesting that all remote RISC-V
+    harts execute a FENCE.I.
+
+    The unused fields in the FENCE.I instruction, _imm[11:0]_, _rs1_, and
+    _rd_, are reserved for finer-grain fences in future extensions. For
+    forward compatibility, base implementations shall ignore these fields,
+    and standard software shall zero these fields.
+    (((FENCE.I, finer-grained)))
+    (((FENCE.I, forward compatibility)))
+
+    [NOTE]
+    ====
+    Because FENCE.I only orders stores with a hart's own instruction
+    fetches, application code should only rely upon FENCE.I if the
+    application thread will not be migrated to a different hart. The EEI can
+    provide mechanisms for efficient multiprocessor instruction-stream
+    synchronization.
+    ====
   definedBy: Zifencei
-  assembly: xs1, xd, imm
+  assembly: ""
   encoding:
     match: -----------------001-----0001111
-    variables:
-    - name: imm
-      location: 31-20
-    - name: rs1
-      location: 19-15
-    - name: rd
-      location: 11-7
   access:
     s: always
     u: always
     vs: always
     vu: always
-  data_independent_timing: true
   operation(): |
-      
+    ifence();