[PATCH v4 1/1] target/riscv: Add Zihintpause support

[Dao Lu]

Added support for RISC-V PAUSE instruction from Zihintpause extension,
enabled by default.

Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Dao Lu <daolu@rivosinc.com>
---
 target/riscv/cpu.c                      |  2 ++
 target/riscv/cpu.h                      |  1 +
 target/riscv/insn32.decode              |  7 ++++++-
 target/riscv/insn_trans/trans_rvi.c.inc | 16 ++++++++++++++++
 4 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index ccacdee215..183fb37fdf 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -825,6 +825,7 @@ static Property riscv_cpu_properties[] = {
     DEFINE_PROP_BOOL("Counters", RISCVCPU, cfg.ext_counters, true),
     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("Zfh", RISCVCPU, cfg.ext_zfh, false),
     DEFINE_PROP_BOOL("Zfhmin", RISCVCPU, cfg.ext_zfhmin, false),
     DEFINE_PROP_BOOL("Zve32f", RISCVCPU, cfg.ext_zve32f, false),
@@ -996,6 +997,7 @@ static void riscv_isa_string_ext(RISCVCPU *cpu, char 
**isa_str, int max_str_len)
      *    extensions by an underscore.
      */
     struct isa_ext_data isa_edata_arr[] = {
+        ISA_EDATA_ENTRY(zihintpause, ext_zihintpause),
         ISA_EDATA_ENTRY(zfh, ext_zfh),
         ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
         ISA_EDATA_ENTRY(zfinx, ext_zfinx),
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index fe6c9a2c92..e466a04a59 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -394,6 +394,7 @@ struct RISCVCPUConfig {
     bool ext_counters;
     bool ext_ifencei;
     bool ext_icsr;
+    bool ext_zihintpause;
     bool ext_svinval;
     bool ext_svnapot;
     bool ext_svpbmt;
diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
index 4033565393..595fdcdad8 100644
--- a/target/riscv/insn32.decode
+++ b/target/riscv/insn32.decode
@@ -149,7 +149,12 @@ srl      0000000 .....    ..... 101 ..... 0110011 @r
 sra      0100000 .....    ..... 101 ..... 0110011 @r
 or       0000000 .....    ..... 110 ..... 0110011 @r
 and      0000000 .....    ..... 111 ..... 0110011 @r
-fence    ---- pred:4 succ:4 ----- 000 ----- 0001111
+
+{
+  pause  0000 0001   0000   00000 000 00000 0001111
+  fence  ---- pred:4 succ:4 ----- 000 ----- 0001111
+}
+
 fence_i  ---- ----   ----   ----- 001 ----- 0001111
 csrrw    ............     ..... 001 ..... 1110011 @csr
 csrrs    ............     ..... 010 ..... 1110011 @csr
diff --git a/target/riscv/insn_trans/trans_rvi.c.inc 
b/target/riscv/insn_trans/trans_rvi.c.inc
index f1342f30f8..2fd07bc2e4 100644
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -796,6 +796,22 @@ static bool trans_srad(DisasContext *ctx, arg_srad *a)
     return gen_shift(ctx, a, EXT_SIGN, tcg_gen_sar_tl, NULL);
 }
 
+static bool trans_pause(DisasContext *ctx, arg_pause *a)
+{
+    if (!ctx->cfg_ptr->ext_zihintpause) {
+        return false;
+    }
+
+    /*
+     * PAUSE is a no-op in QEMU,
+     * end the TB and return to main loop
+     */
+    gen_set_pc_imm(ctx, ctx->pc_succ_insn);
+    tcg_gen_exit_tb(NULL, 0);
+    ctx->base.is_jmp = DISAS_NORETURN;
+
+    return true;
+}
 
 static bool trans_fence(DisasContext *ctx, arg_fence *a)
 {
-- 
2.25.1