target/riscv: support disable auto fence

Support disable automatic fence, it's useful for
debug some cache related issue.

doc/openocd.texi

@@ -11631,6 +11631,19 @@ riscv exec_progbuf 0x0330000f 0x0000100f
 riscv exec_progbuf 0x94a20405
 @end example
 
+@deffn {Command} {riscv autofence} [on|off]
+When on (default), OpenOCD will automatically execute RISC-V fence instructions
+(@var{fence.i} and @var{fence rw, rw}) in these cases:
+@itemize @bullet
+@item before step or resume,
+@item before memory read via the Program Buffer,
+@item after memory write via the Program Buffer.
+@end itemize
+When off, users need to take care of memory coherency themselves, for example
+using the @var{riscv exec_progbuf} command to execute fences or CMO instructions
+(RISC-V Cache Management Operations).
+@end deffn
+
 @section ARC Architecture
 @cindex ARC
 

src/target/riscv/riscv-013.c

@@ -2913,11 +2913,15 @@ static int deassert_reset(struct target *target)
 	return dm_write(target, DM_DMCONTROL, control);
 }
 
-static int execute_fence(struct target *target)
+static int execute_autofence(struct target *target)
 {
 	if (dm013_select_target(target) != ERROR_OK)
 		return ERROR_FAIL;
 
+	RISCV_INFO(r);
+	if (!r->autofence)
+		return ERROR_OK;
+
 	/* FIXME: For non-coherent systems we need to flush the caches right
 	 * here, but there's no ISA-defined way of doing that. */
 	struct riscv_program program;
@@ -2939,8 +2943,9 @@ static int execute_fence(struct target *target)
 				LOG_TARGET_ERROR(target, "Unexpected error during fence execution");
 				return ERROR_FAIL;
 			}
-			LOG_TARGET_DEBUG(target, "Unable to execute fence");
+			LOG_TARGET_DEBUG(target, "Unable to execute fence.i and fence rw, rw");
 		}
+		LOG_TARGET_DEBUG(target, "Successfully executed fence.i and fence rw, rw");
 		return ERROR_OK;
 	}
 
@@ -2954,6 +2959,7 @@ static int execute_fence(struct target *target)
 			}
 			LOG_TARGET_DEBUG(target, "Unable to execute fence.i");
 		}
+		LOG_TARGET_DEBUG(target, "Successfully executed fence.i");
 
 		riscv_program_init(&program, target);
 		riscv_program_fence_rw_rw(&program);
@@ -2964,6 +2970,7 @@ static int execute_fence(struct target *target)
 			}
 			LOG_TARGET_DEBUG(target, "Unable to execute fence rw, rw");
 		}
+		LOG_TARGET_DEBUG(target, "Successfully executed fence rw, rw");
 		return ERROR_OK;
 	}
 
@@ -4273,7 +4280,7 @@ read_memory_progbuf(struct target *target, target_addr_t address,
 
 	memset(buffer, 0, count*size);
 
-	if (execute_fence(target) != ERROR_OK)
+	if (execute_autofence(target) != ERROR_OK)
 		return MEM_ACCESS_SKIPPED_FENCE_EXEC_FAILED;
 
 	uint64_t mstatus = 0;
@@ -4864,7 +4871,7 @@ write_memory_progbuf(struct target *target, target_addr_t address,
 		if (register_write_direct(target, GDB_REGNO_MSTATUS, mstatus_old))
 			return MEM_ACCESS_FAILED;
 
-	if (execute_fence(target) != ERROR_OK)
+	if (execute_autofence(target) != ERROR_OK)
 		return MEM_ACCESS_SKIPPED_FENCE_EXEC_FAILED;
 
 	return result == ERROR_OK ? MEM_ACCESS_OK : MEM_ACCESS_FAILED;
@@ -5351,17 +5358,11 @@ static int riscv013_get_dmi_scan_length(struct target *target)
 	return info->abits + DTM_DMI_DATA_LENGTH + DTM_DMI_OP_LENGTH;
 }
 
-static int maybe_execute_fence_i(struct target *target)
-{
-	if (has_sufficient_progbuf(target, 2))
-		return execute_fence(target);
-	return ERROR_OK;
-}
-
 /* Helper Functions. */
 static int riscv013_on_step_or_resume(struct target *target, bool step)
 {
-	if (maybe_execute_fence_i(target) != ERROR_OK)
+	if (has_sufficient_progbuf(target, 2))
+		if (execute_autofence(target) != ERROR_OK)
 			return ERROR_FAIL;
 
 	if (set_dcsr_ebreak(target, step) != ERROR_OK)

src/target/riscv/riscv.c

@@ -4521,6 +4521,22 @@ COMMAND_HANDLER(riscv_set_maskisr)
 	return ERROR_OK;
 }
 
+COMMAND_HANDLER(riscv_set_autofence)
+{
+	struct target *target = get_current_target(CMD_CTX);
+	RISCV_INFO(r);
+
+	if (CMD_ARGC == 0) {
+		command_print(CMD, "autofence: %s", r->autofence ? "on" : "off");
+		return ERROR_OK;
+	} else if (CMD_ARGC == 1) {
+		COMMAND_PARSE_ON_OFF(CMD_ARGV[0], r->autofence);
+		return ERROR_OK;
+	}
+
+	return ERROR_COMMAND_SYNTAX_ERROR;
+}
+
 COMMAND_HANDLER(riscv_set_ebreakm)
 {
 	struct target *target = get_current_target(CMD_CTX);
@@ -5428,6 +5444,15 @@ static const struct command_registration riscv_exec_command_handlers[] = {
 				"hw - translate vaddr to paddr by hardware, "
 				"off - no address translation."
 	},
+	{
+		.name = "autofence",
+		.handler = riscv_set_autofence,
+		.mode = COMMAND_ANY,
+		.usage = "[on|off]",
+		.help = "When on (default), OpenOCD will automatically execute fence instructions in some situations. "
+			"When off, users need to take care of memory coherency themselves, for example by using "
+			"`riscv exec_progbuf` to execute fence or CMO instructions."
+	},
 	COMMAND_REGISTRATION_DONE
 };
 
@@ -5569,6 +5594,8 @@ static void riscv_info_init(struct target *target, struct riscv_info *r)
 	r->wp_allow_equality_match_trigger = true;
 	r->wp_allow_ge_lt_trigger = true;
 	r->wp_allow_napot_trigger = true;
+
+	r->autofence = true;
 }
 
 static int riscv_resume_go_all_harts(struct target *target)

src/target/riscv/riscv.h

@@ -321,6 +321,8 @@ struct riscv_info {
 	bool wp_allow_equality_match_trigger;
 	bool wp_allow_napot_trigger;
 	bool wp_allow_ge_lt_trigger;
+
+	bool autofence;
 };
 
 COMMAND_HELPER(riscv_print_info_line, const char *section, const char *key,