From fd7006f4f1a34d6bbfe0c7d62be72ced43281462 Mon Sep 17 00:00:00 2001
From: Melissa Jost <melissakjost@gmail.com>
Date: Fri, 3 Mar 2023 17:24:58 -0800
Subject: [PATCH] arch-riscv: Revert CSR instruction fixes

This reverts commit 4b1c24542065380c6cff7ab2baa25e216a0ad38e
and commit 89c49d1ab06ea5364ab1f80586f8b01c0297cb12 because
they are causing the RISC-V Ubuntu boot test within the
nightly tests to hang and time out.

Change-Id: Ia4d8098ec940cb5900256c8cede0146256c851e5
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/68637
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Roger Chang <rogerycchang@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
---
 src/arch/riscv/insts/standard.hh        | 19 ++-----------------
 src/arch/riscv/isa/formats/standard.isa | 15 ++++++---------
 2 files changed, 8 insertions(+), 26 deletions(-)

diff --git a/src/arch/riscv/insts/standard.hh b/src/arch/riscv/insts/standard.hh
index 2dfe73aedf..5b0e8c2c22 100644
--- a/src/arch/riscv/insts/standard.hh
+++ b/src/arch/riscv/insts/standard.hh
@@ -91,33 +91,18 @@ class CSROp : public RiscvStaticInst
   protected:
     uint64_t csr;
     uint64_t uimm;
-    bool read;
-    bool write;
 
     /// Constructor
     CSROp(const char *mnem, ExtMachInst _machInst, OpClass __opClass)
         : RiscvStaticInst(mnem, _machInst, __opClass),
-            csr(FUNCT12), uimm(CSRIMM), read(true), write(true)
+            csr(FUNCT12), uimm(CSRIMM)
     {
         if (csr == CSR_SATP) {
             flags[IsSquashAfter] = true;
         }
-        if (strcmp(mnemonic, "csrrw") == 0 ||
-            strcmp(mnemonic, "csrrwi") == 0) {
-          if (RD == 0){
-            read = false;
-          }
-        } else if (strcmp(mnemonic, "csrrs") == 0 ||
-                   strcmp(mnemonic, "csrrc") == 0 ||
-                   strcmp(mnemonic, "csrrsi") == 0 ||
-                   strcmp(mnemonic, "csrrci") == 0 ){
-          if (RS1 == 0 || uimm == 0) {
-            write = false;
-          }
-        }
     }
 
-  std::string generateDisassembly(
+    std::string generateDisassembly(
         Addr pc, const loader::SymbolTable *symtab) const override;
 };
 
diff --git a/src/arch/riscv/isa/formats/standard.isa b/src/arch/riscv/isa/formats/standard.isa
index c94a0bcdbd..bb500f5f49 100644
--- a/src/arch/riscv/isa/formats/standard.isa
+++ b/src/arch/riscv/isa/formats/standard.isa
@@ -358,7 +358,7 @@ def template CSRExecute {{
         %(op_decl)s;
         %(op_rd)s;
 
-        RegVal data = 0, olddata = 0, nonmaskdata = 0;
+        RegVal data, olddata;
         auto lowestAllowedMode = (PrivilegeMode)bits(csr, 9, 8);
         auto pm = (PrivilegeMode)xc->readMiscReg(MISCREG_PRV);
         if (pm < lowestAllowedMode) {
@@ -380,13 +380,11 @@ def template CSRExecute {{
             break;
         }
 
-        if (read) {
-          if (csr == CSR_FCSR) {
+        if (csr == CSR_FCSR) {
             olddata = xc->readMiscReg(MISCREG_FFLAGS) |
-              (xc->readMiscReg(MISCREG_FRM) << FRM_OFFSET);
-          } else {
+                      (xc->readMiscReg(MISCREG_FRM) << FRM_OFFSET);
+        } else {
             olddata = xc->readMiscReg(midx);
-          }
         }
         olddata = rvZext(olddata);
         auto olddata_all = olddata;
@@ -397,9 +395,8 @@ def template CSRExecute {{
 
         %(code)s;
 
-        nonmaskdata = data & ~maskVal;
         data &= maskVal;
-        if (write) {
+        if (data != olddata) {
             if (bits(csr, 11, 10) == 0x3) {
                 return std::make_shared<IllegalInstFault>(
                         csprintf("CSR %s is read-only\n", csrName), machInst);
@@ -420,7 +417,7 @@ def template CSRExecute {{
               case CSR_SIP: case CSR_SIE:
               case CSR_UIP: case CSR_UIE:
               case CSR_MSTATUS: case CSR_SSTATUS: case CSR_USTATUS:
-                if (nonmaskdata == 0) {
+                if (newdata_all != olddata_all) {
                     xc->setMiscReg(midx, newdata_all);
                 } else {
                     return std::make_shared<IllegalInstFault>(