lib: sbi_illegal_insn: Add emulation for fence.tso

While OpenC906 appears to properly decode `fence.tso` as a fence instruction[1], the version of the C906 taped out in the Allwinner D1 does not, and raises illegal instruction. Handle this errata by emulating `fence.tso` as `fence rw, rw`. [1]: https://github.com/T-head-Semi/openc906/blob/30827e7f/C906_RTL_FACTORY/gen_rtl/idu/rtl/aq_idu_id_decd.v#L2097 Signed-off-by: Samuel Holland <[email protected]> Reviewed-by: Anup Patel <[email protected]>
milkv-duo · Apr 9, 2024 · d009644 · d009644
1 parent 1bd2e81
commit d009644
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Showing 2 changed files with 16 additions and 1 deletion.
diff --git a/opensbi/include/sbi/riscv_encoding.h b/opensbi/include/sbi/riscv_encoding.h
@@ -625,6 +625,9 @@
 #define INSN_MASK_WFI			0xffffff00
 #define INSN_MATCH_WFI			0x10500000
 
+#define INSN_MASK_FENCE_TSO		0xffffffff
+#define INSN_MATCH_FENCE_TSO		0x8330000f
+
 #define INSN_16BIT_MASK			0x3
 #define INSN_32BIT_MASK			0x1c
 

diff --git a/opensbi/lib/sbi/sbi_illegal_insn.c b/opensbi/lib/sbi/sbi_illegal_insn.c
@@ -8,6 +8,7 @@
  */
 
 #include <sbi/riscv_asm.h>
+#include <sbi/riscv_barrier.h>
 #include <sbi/riscv_encoding.h>
 #include <sbi/sbi_bitops.h>
 #include <sbi/sbi_emulate_csr.h>
@@ -31,6 +32,17 @@ static int truly_illegal_insn(ulong insn, struct sbi_trap_regs *regs)
 	return sbi_trap_redirect(regs, &trap);
 }
 
+static int misc_mem_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
+{
+	/* Errata workaround: emulate `fence.tso` as `fence rw, rw`. */
+	if ((insn & INSN_MASK_FENCE_TSO) == INSN_MATCH_FENCE_TSO) {
+		smp_mb();
+		return 0;
+	}
+
+	return truly_illegal_insn(insn, regs);
+}
+
 static int system_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
 {
 	int do_write, rs1_num = (insn >> 15) & 0x1f;
@@ -83,7 +95,7 @@ static illegal_insn_func illegal_insn_table[32] = {
 	truly_illegal_insn, /* 0 */
 	truly_illegal_insn, /* 1 */
 	truly_illegal_insn, /* 2 */
-	truly_illegal_insn, /* 3 */
+	misc_mem_opcode_insn, /* 3 */
 	truly_illegal_insn, /* 4 */
 	truly_illegal_insn, /* 5 */
 	truly_illegal_insn, /* 6 */