RISC-V: Add Zawrs ISA extension support

This patch adds support for the Zawrs ISA extension.
Given the current (incomplete) implementation of reservation sets
there seems to be no way to provide a full emulation of the WRS
instruction (wake on reservation set invalidation or timeout or
interrupt). Therefore, we just exit the TB and return to the main loop.

The specification can be found here:
  https://github.com/riscv/riscv-zawrs/blob/main/zawrs.adoc

Note, that the Zawrs extension is frozen, but not ratified yet.

Changes since v3:
* Remove "RFC" since the extension is frozen
* Rebase on master and fix integration issues
* Fix entry ordering in extension list

Changes since v2:
* Rebase on master and resolve conflicts
* Adjustments according to a specification change
* Inline REQUIRE_ZAWRS() since it has only one user

Changes since v1:
* Adding zawrs to the ISA string that is passed to the kernel

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20221005144948.3421504-1-christoph.muellner@vrull.eu>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

@@ -76,6 +76,7 @@ static const struct isa_ext_data isa_edata_arr[] = {
     ISA_EXT_DATA_ENTRY(zicsr, true, PRIV_VERSION_1_10_0, ext_icsr),
     ISA_EXT_DATA_ENTRY(zifencei, true, PRIV_VERSION_1_10_0, ext_ifencei),
     ISA_EXT_DATA_ENTRY(zihintpause, true, PRIV_VERSION_1_10_0, ext_zihintpause),
+    ISA_EXT_DATA_ENTRY(zawrs, true, PRIV_VERSION_1_12_0, ext_zawrs),
     ISA_EXT_DATA_ENTRY(zfh, true, PRIV_VERSION_1_12_0, ext_zfh),
     ISA_EXT_DATA_ENTRY(zfhmin, true, PRIV_VERSION_1_12_0, ext_zfhmin),
     ISA_EXT_DATA_ENTRY(zfinx, true, PRIV_VERSION_1_12_0, ext_zfinx),
@@ -766,6 +767,11 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
             return;
         }
 
+        if ((cpu->cfg.ext_zawrs) && !cpu->cfg.ext_a) {
+            error_setg(errp, "Zawrs extension requires A extension");
+            return;
+        }
+
         if ((cpu->cfg.ext_zfh || cpu->cfg.ext_zfhmin) && !cpu->cfg.ext_f) {
             error_setg(errp, "Zfh/Zfhmin extensions require F extension");
             return;
@@ -1021,6 +1027,7 @@ static Property riscv_cpu_extensions[] = {
     DEFINE_PROP_BOOL("Zifencei", RISCVCPU, cfg.ext_ifencei, true),
     DEFINE_PROP_BOOL("Zicsr", RISCVCPU, cfg.ext_icsr, true),
     DEFINE_PROP_BOOL("Zihintpause", RISCVCPU, cfg.ext_zihintpause, true),
+    DEFINE_PROP_BOOL("Zawrs", RISCVCPU, cfg.ext_zawrs, true),
     DEFINE_PROP_BOOL("Zfh", RISCVCPU, cfg.ext_zfh, false),
     DEFINE_PROP_BOOL("Zfhmin", RISCVCPU, cfg.ext_zfhmin, false),
     DEFINE_PROP_BOOL("Zve32f", RISCVCPU, cfg.ext_zve32f, false),

target/riscv/cpu.h

@@ -453,6 +453,7 @@ struct RISCVCPUConfig {
     bool ext_svnapot;
     bool ext_svpbmt;
     bool ext_zdinx;
+    bool ext_zawrs;
     bool ext_zfh;
     bool ext_zfhmin;
     bool ext_zfinx;

target/riscv/insn32.decode

@@ -718,6 +718,10 @@ vsetvli         0 ........... ..... 111 ..... 1010111  @r2_zimm11
 vsetivli        11 .......... ..... 111 ..... 1010111  @r2_zimm10
 vsetvl          1000000 ..... ..... 111 ..... 1010111  @r
 
+# *** Zawrs Standard Extension ***
+wrs_nto    000000001101 00000 000 00000 1110011
+wrs_sto    000000011101 00000 000 00000 1110011
+
 # *** RV32 Zba Standard Extension ***
 sh1add     0010000 .......... 010 ..... 0110011 @r
 sh2add     0010000 .......... 100 ..... 0110011 @r

target/riscv/insn_trans/trans_rvzawrs.c.inc

@@ -0,0 +1,51 @@
+/*
+ * RISC-V translation routines for the RISC-V Zawrs Extension.
+ *
+ * Copyright (c) 2022 Christoph Muellner, christoph.muellner@vrull.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2 or later, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+static bool trans_wrs(DisasContext *ctx)
+{
+    if (!ctx->cfg_ptr->ext_zawrs) {
+        return false;
+    }
+
+    /*
+     * The specification says:
+     * While stalled, an implementation is permitted to occasionally
+     * terminate the stall and complete execution for any reason.
+     *
+     * So let's just exit TB and return to the main loop.
+     */
+
+    /* Clear the load reservation  (if any).  */
+    tcg_gen_movi_tl(load_res, -1);
+
+    gen_set_pc_imm(ctx, ctx->pc_succ_insn);
+    tcg_gen_exit_tb(NULL, 0);
+    ctx->base.is_jmp = DISAS_NORETURN;
+
+    return true;
+}
+
+#define GEN_TRANS_WRS(insn)                                     \
+static bool trans_ ## insn(DisasContext *ctx, arg_ ## insn *a)  \
+{                                                               \
+    (void)a;                                                    \
+    return trans_wrs(ctx);                                      \
+}
+
+GEN_TRANS_WRS(wrs_nto)
+GEN_TRANS_WRS(wrs_sto)

target/riscv/translate.c

@@ -1060,6 +1060,7 @@ static uint32_t opcode_at(DisasContextBase *dcbase, target_ulong pc)
 #include "insn_trans/trans_rvh.c.inc"
 #include "insn_trans/trans_rvv.c.inc"
 #include "insn_trans/trans_rvb.c.inc"
+#include "insn_trans/trans_rvzawrs.c.inc"
 #include "insn_trans/trans_rvzfh.c.inc"
 #include "insn_trans/trans_rvk.c.inc"
 #include "insn_trans/trans_privileged.c.inc"