commit 4696f0ab5c436ed53567ce6baec67c921d9b70ae
author Dao Lu <daolu@rivosinc.com> Sun Jul 24 20:47:28 2022 -0700
committer Alistair Francis <alistair.francis@wdc.com> Wed Sep 07 09:18:33 2022 +0200
tree 435b5069b3fb5f03bff74765763330893bc84f10
parent 1ad3f9bdc76c83b23d689a111d5a160c528ac8ba

target/riscv: Add Zihintpause support

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

Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Dao Lu <daolu@rivosinc.com>
Message-Id: <20220725034728.2620750-2-daolu@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.c

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 966e5f2..d4635c7 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -73,6 +73,7 @@
     ISA_EXT_DATA_ENTRY(v, false, PRIV_VERSION_1_12_0, ext_v),
     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(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),
@@ -987,6 +988,7 @@
     DEFINE_PROP_UINT8("pmu-num", RISCVCPU, cfg.pmu_num, 16),
     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),

target/riscv/cpu.h

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 561d7fa..4be4b82 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -426,6 +426,7 @@
     bool ext_zkt;
     bool ext_ifencei;
     bool ext_icsr;
+    bool ext_zihintpause;
     bool ext_svinval;
     bool ext_svnapot;
     bool ext_svpbmt;

target/riscv/insn32.decode

diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
index 4033565..595fdcd 100644
--- a/target/riscv/insn32.decode
+++ b/target/riscv/insn32.decode
@@ -149,7 +149,12 @@
 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

target/riscv/insn_trans/trans_rvi.c.inc

diff --git a/target/riscv/insn_trans/trans_rvi.c.inc b/target/riscv/insn_trans/trans_rvi.c.inc
index ca8e3d1..c49dbec 100644
--- a/target/riscv/insn_trans/trans_rvi.c.inc
+++ b/target/riscv/insn_trans/trans_rvi.c.inc
@@ -792,6 +792,22 @@
     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)
 {