sysreset: Support a hot reset

In some cases we may wish to return back to the program which started
U-Boot. Add the concept of a 'hot' reset, to support this.

Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/boot.c

@@ -60,6 +60,7 @@ U_BOOT_CMD(
 	reset, 2, 0,	do_reset,
 	"Perform RESET of the CPU",
 	"- cold boot without level specifier\n"
+	"reset -h - hotreset if implemented\n"
 	"reset -w - warm reset if implemented"
 );
 

doc/usage/cmd/reset.rst

@@ -22,6 +22,9 @@ DDR and peripherals, on some boards also resets external PMIC.
 -w
     Do warm WARM, reset CPU but keep peripheral/DDR/PMIC active.
 
+-h
+    Do a hot reset, if supported, which returns back to the program which
+    started U-Boot.
 
 Return value
 ------------

drivers/sysreset/sysreset-uclass.c

@@ -125,8 +125,19 @@ int do_reset(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 	if (argc > 2)
 		return CMD_RET_USAGE;
 
-	if (argc == 2 && argv[1][0] == '-' && argv[1][1] == 'w') {
-		reset_type = SYSRESET_WARM;
+	if (argc == 2 && argv[1][0] == '-') {
+		int type = argv[1][1];
+
+		switch (type) {
+		case 'h':
+			reset_type = SYSRESET_HOT;
+			break;
+		case 'w':
+			reset_type = SYSRESET_WARM;
+			break;
+		default:
+			return CMD_RET_USAGE;
+		}
 	}
 
 	printf("resetting ...\n");

drivers/sysreset/sysreset_sandbox.c

@@ -65,6 +65,7 @@ static int sandbox_sysreset_request(struct udevice *dev, enum sysreset_t type)
 			return -EACCES;
 		sandbox_exit();
 	case SYSRESET_POWER:
+	case SYSRESET_HOT:
 		if (!state->sysreset_allowed[type])
 			return -EACCES;
 		sandbox_exit();

include/sysreset.h

@@ -21,6 +21,9 @@ enum sysreset_t {
 	SYSRESET_POWER,
 	/** @SYSRESET_POWER_OFF: turn off power */
 	SYSRESET_POWER_OFF,
+	/** @SYSRESET_HOT: exit out of U-Boot (e.g. from EFI app) */
+	SYSRESET_HOT,
+
 	/** @SYSRESET_COUNT: number of available reset types */
 	SYSRESET_COUNT,
 };

test/dm/sysreset.c

@@ -76,10 +76,12 @@ static int dm_test_sysreset_walk(struct unit_test_state *uts)
 	state->sysreset_allowed[SYSRESET_COLD] = false;
 	state->sysreset_allowed[SYSRESET_POWER] = false;
 	state->sysreset_allowed[SYSRESET_POWER_OFF] = false;
+	state->sysreset_allowed[SYSRESET_HOT] = false;
 	ut_asserteq(-EACCES, sysreset_walk(SYSRESET_WARM));
 	ut_asserteq(-EACCES, sysreset_walk(SYSRESET_COLD));
 	ut_asserteq(-EACCES, sysreset_walk(SYSRESET_POWER));
 	ut_asserteq(-EACCES, sysreset_walk(SYSRESET_POWER_OFF));
+	ut_asserteq(-EACCES, sysreset_walk(SYSRESET_HOT));
 
 	/*
 	 * Enable cold system reset - this should make cold system reset work,