Make resume order configurable. (#388)

* Make resume order configurable.

This is a customer requirement. Using this option is discouraged.

Change-Id: I520ec19cc23d7837cb8576f69dadf2b922fa2628

* Fix style.

Change-Id: If8e515984c92ce8df52aa69e87abde023897409f

* Make mingw32-gcc happy.

Change-Id: I39852aedec293294b2b2638ab2cc45494fe77beb

doc/openocd.texi

@@ -9491,6 +9491,17 @@ When on, prefer to use System Bus Access to access memory.  When off, prefer to
 use the Program Buffer to access memory.
 @end deffn
 
+@deffn Command {riscv resume_order} normal|reversed
+Some software assumes all harts are executing nearly continuously. Such
+software may be sensitive to the order that harts are resumed in. On harts
+that don't support hasel, this option allows the user to choose the order the
+harts are resumed in. If you are using this option, it's probably masking a
+race condition problem in your code.
+
+Normal order is from lowest hart index to highest. This is the default
+behavior. Reversed order is from highest hart index to lowest.
+@end deffn
+
 @deffn Command {riscv set_ir} (@option{idcode}|@option{dtmcs}|@option{dmi}) [value]
 Set the IR value for the specified JTAG register.  This is useful, for
 example, when using the existing JTAG interface on a Xilinx FPGA by

src/target/riscv/riscv.c

@@ -264,6 +264,11 @@ range_t *expose_csr;
 /* Same, but for custom registers. */
 range_t *expose_custom;
 
+static enum {
+	RO_NORMAL,
+	RO_REVERSED
+} resume_order;
+
 static int riscv_resume_go_all_harts(struct target *target);
 
 void select_dmi_via_bscan(struct target *target)
@@ -2141,18 +2146,35 @@ COMMAND_HANDLER(riscv_set_ir)
 	uint32_t value;
 	COMMAND_PARSE_NUMBER(u32, CMD_ARGV[1], value);
 
-	if (!strcmp(CMD_ARGV[0], "idcode")) {
+	if (!strcmp(CMD_ARGV[0], "idcode"))
 		buf_set_u32(ir_idcode, 0, 32, value);
-		return ERROR_OK;
+	else if (!strcmp(CMD_ARGV[0], "dtmcs"))
-	} else if (!strcmp(CMD_ARGV[0], "dtmcs")) {
 		buf_set_u32(ir_dtmcontrol, 0, 32, value);
-		return ERROR_OK;
+	else if (!strcmp(CMD_ARGV[0], "dmi"))
-	} else if (!strcmp(CMD_ARGV[0], "dmi")) {
 		buf_set_u32(ir_dbus, 0, 32, value);
+	else
+		return ERROR_FAIL;
+
 	return ERROR_OK;
+}
+
+COMMAND_HANDLER(riscv_resume_order)
+{
+	if (CMD_ARGC > 1) {
+		LOG_ERROR("Command takes at most one argument");
+		return ERROR_COMMAND_SYNTAX_ERROR;
+	}
+
+	if (!strcmp(CMD_ARGV[0], "normal")) {
+		resume_order = RO_NORMAL;
+	} else if (!strcmp(CMD_ARGV[0], "reversed")) {
+		resume_order = RO_REVERSED;
 	} else {
+		LOG_ERROR("Unsupported resume order: %s", CMD_ARGV[0]);
 		return ERROR_FAIL;
 	}
+
+	return ERROR_OK;
 }
 
 COMMAND_HANDLER(riscv_use_bscan_tunnel)
@@ -2280,6 +2302,15 @@ static const struct command_registration riscv_exec_command_handlers[] = {
 			"command resets those learned values after `wait` scans. It's only "
 			"useful for testing OpenOCD itself."
 	},
+	{
+		.name = "resume_order",
+		.handler = riscv_resume_order,
+		.mode = COMMAND_ANY,
+		.usage = "resume_order normal|reversed",
+		.help = "Choose the order that harts are resumed in when `hasel` is not "
+			"supported. Normal order is from lowest hart index to highest. "
+			"Reversed order is from highest hart index to lowest."
+	},
 	{
 		.name = "set_ir",
 		.handler = riscv_set_ir,
@@ -2437,7 +2468,27 @@ void riscv_info_init(struct target *target, riscv_info_t *r)
 static int riscv_resume_go_all_harts(struct target *target)
 {
 	RISCV_INFO(r);
-	for (int i = 0; i < riscv_count_harts(target); ++i) {
+
+	/* Dummy variables to make mingw32-gcc happy. */
+	int first = 0;
+	int last = 1;
+	int step = 1;
+	switch (resume_order) {
+		case RO_NORMAL:
+			first = 0;
+			last = riscv_count_harts(target) - 1;
+			step = 1;
+			break;
+		case RO_REVERSED:
+			first = riscv_count_harts(target) - 1;
+			last = 0;
+			step = -1;
+			break;
+		default:
+			assert(0);
+	}
+
+	for (int i = first; i != last + step; i += step) {
 		if (!riscv_hart_enabled(target, i))
 			continue;