restart: add reset -w for warm bootrom reset

We currently support reboot mode communication with BootROMs of the
i.MX6Q/DL, i.MX8MM and STM32MP15x. For each of these, the user must
take care to use the correct reset as the highest priority reset often
clears the non-volatile register mapped by the syscon holding the reboot
mode. As we only have one BootROM, we can improve usability by adding a
global flag that describes whether a restart handler is suitable for
use after a bootrom reboot mode write. Add a flag bit describing this
and allow populating it from the device tree as well as from drivers.

Existing i.MX/STM32 drivers will be moved onto this in follow-up
commits.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20221017071000.1458292-4-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

6 files changed, 39 insertions, 13 deletions

diff --git a/Documentation/boards/imx.rst b/Documentation/boards/imx.rst
index 4ce9d9808c..6c16923340 100644
--- a/Documentation/boards/imx.rst
+++ b/Documentation/boards/imx.rst
@@ -105,7 +105,7 @@ that BootROM should select after a warm reset::
           mode-serial = <0x10 0x40000000>;
   };
 
-  barebox@FSL i.MX8MM EVK board:/ gpr.reboot_mode.next=serial reset -r imxwd-warm
+  barebox@FSL i.MX8MM EVK board:/ gpr.reboot_mode.next=serial reset -w
 
 This will cause barebox to fall into serial download mode on an i.MX8MM.
 
diff --git a/Documentation/devicetree/bindings/power/restart.rst b/Documentation/devicetree/bindings/power/restart.rst
index 8c866f6e0d..42b87f7e9c 100644
--- a/Documentation/devicetree/bindings/power/restart.rst
+++ b/Documentation/devicetree/bindings/power/restart.rst
@@ -8,3 +8,8 @@ Optional properties:
 - ``restart-priority`` : Overrides the priority set by the driver. Normally,
   the device with the biggest reach should reset the system.
   See :ref:`_system_reset` for more information.
+
+- ``barebox,restart-warm-bootrom`` : Restart will not cause loss to non-volatile
+  registers sampled by the bootrom at startup. This is a necessary precondition
+  for working :ref:`reboot_mode` communication between barebox and the SoC's
+  BootROM.
diff --git a/Documentation/user/reboot-mode.rst b/Documentation/user/reboot-mode.rst
index 83d4136b85..1929a67e0b 100644
--- a/Documentation/user/reboot-mode.rst
+++ b/Documentation/user/reboot-mode.rst
@@ -47,7 +47,9 @@ Reboot mode providers have priorities. The provider with the highest
 priority has its parameters aliased as ``$global.system.reboot_mode.prev``
 and ``$global.system.reboot_mode.next``. After executing the init scripts,
 barebox startup will ``source /env/bmode/${global.system.reboot_mode.prev}``
-if available.
+if available. Example usage::
+
+	gpr.reboot_mode=serial reset -w
 
 Reset
 =====
@@ -60,6 +62,9 @@ If such reboot mode storage is used, users must take care to use the correct
 reset provider. In barebox, multiple reset providers may co-exist. The
 ``reset`` command allows listing and choosing a specific reboot mode.
 
+For communication with the SoC's BootROM, a warm reset can be triggered
+with ``reset -w`` if a suitable reset handler has been registered.
+
 Disambiguation
 ==============
 
diff --git a/commands/reset.c b/commands/reset.c
index fe54e2f9b4..88e677afab 100644
--- a/commands/reset.c
+++ b/commands/reset.c
@@ -12,12 +12,12 @@
 static int cmd_reset(int argc, char *argv[])
 {
 	struct restart_handler *rst;
-	int opt, shutdown_flag;
+	int opt, shutdown_flag, flags = 0;
 	const char *name = NULL;
 
 	shutdown_flag = 1;
 
-	while ((opt = getopt(argc, argv, "flr:")) > 0) {
+	while ((opt = getopt(argc, argv, "flwr:")) > 0) {
 		switch (opt) {
 		case 'f':
 			shutdown_flag = 0;
@@ -25,6 +25,9 @@ static int cmd_reset(int argc, char *argv[])
 		case 'l':
 			restart_handlers_print();
 			return 0;
+		case 'w':
+			flags |= RESTART_FLAG_WARM_BOOTROM;
+			break;
 		case 'r':
 			name = optarg;
 			break;
@@ -33,9 +36,9 @@ static int cmd_reset(int argc, char *argv[])
 		}
 	}
 
-	rst = restart_handler_get_by_name(name);
-	if (!rst && name) {
-		printf("reset '%s' does not exist\n", name);
+	rst = restart_handler_get_by_name(name, flags);
+	if (!rst && (name || flags)) {
+		printf("No matching restart handler found\n");
 		return COMMAND_ERROR;
 	}
 
@@ -57,13 +60,14 @@ BAREBOX_CMD_HELP_START(reset)
 BAREBOX_CMD_HELP_TEXT("Options:")
 BAREBOX_CMD_HELP_OPT("-f",  "force RESET, don't call shutdown")
 BAREBOX_CMD_HELP_OPT("-l",  "list reset handlers")
+BAREBOX_CMD_HELP_OPT("-w",  "only consider warm BootROM reboot-mode-preserving resets")
 BAREBOX_CMD_HELP_OPT("-r RESET",  "use reset handler named RESET")
 BAREBOX_CMD_HELP_END
 
 BAREBOX_CMD_START(reset)
 	.cmd		= cmd_reset,
 	BAREBOX_CMD_DESC("perform RESET of the CPU")
-	BAREBOX_CMD_OPTS("[-flr]")
+	BAREBOX_CMD_OPTS("[-flrw]")
 	BAREBOX_CMD_GROUP(CMD_GRP_BOOT)
 	BAREBOX_CMD_HELP(cmd_reset_help)
 	BAREBOX_CMD_COMPLETE(empty_complete)
diff --git a/common/restart.c b/common/restart.c
index 9e988838bc..0294b36ecc 100644
--- a/common/restart.c
+++ b/common/restart.c
@@ -30,6 +30,9 @@ int restart_handler_register(struct restart_handler *rst)
 	if (rst->of_node) {
 		of_property_read_u32(rst->of_node, "restart-priority",
 				     &rst->priority);
+		if (of_property_read_bool(rst->of_node,
+					  "barebox,restart-warm-bootrom"))
+			rst->flags |= RESTART_FLAG_WARM_BOOTROM;
 	}
 
 	list_add_tail(&rst->list, &restart_handler_list);
@@ -73,7 +76,7 @@ int restart_handler_register_fn(const char *name,
 /**
  * restart_handler_get_by_name() - reset the whole system
  */
-struct restart_handler *restart_handler_get_by_name(const char *name)
+struct restart_handler *restart_handler_get_by_name(const char *name, int flags)
 {
 	struct restart_handler *rst = NULL, *tmp;
 	unsigned int priority = 0;
@@ -81,6 +84,8 @@ struct restart_handler *restart_handler_get_by_name(const char *name)
 	list_for_each_entry(tmp, &restart_handler_list, list) {
 		if (name && tmp->name && strcmp(name, tmp->name))
 			continue;
+		if (flags && (tmp->flags & flags) != flags)
+			continue;
 		if (tmp->priority > priority) {
 			priority = tmp->priority;
 			rst = tmp;
@@ -97,7 +102,7 @@ void __noreturn restart_machine(void)
 {
 	struct restart_handler *rst;
 
-	rst = restart_handler_get_by_name(NULL);
+	rst = restart_handler_get_by_name(NULL, 0);
 	if (rst) {
 		pr_debug("%s: using restart handler %s\n", __func__, rst->name);
 		console_flush();
@@ -114,6 +119,10 @@ void restart_handlers_print(void)
 {
 	struct restart_handler *tmp;
 
-	list_for_each_entry(tmp, &restart_handler_list, list)
-		printf("%-20s %6d\n", tmp->name, tmp->priority);
+	list_for_each_entry(tmp, &restart_handler_list, list) {
+		printf("%-20s %6d ", tmp->name, tmp->priority);
+		if (tmp->flags & RESTART_FLAG_WARM_BOOTROM)
+			putchar('W');
+		putchar('\n');
+	}
 }
diff --git a/include/restart.h b/include/restart.h
index 330b50a53a..15f30bb7ad 100644
--- a/include/restart.h
+++ b/include/restart.h
@@ -4,18 +4,21 @@
 
 #include <linux/compiler.h>
 #include <linux/types.h>
+#include <linux/bitops.h>
 
 struct device_node;
 
 void restart_handlers_print(void);
 void __noreturn restart_machine(void);
-struct restart_handler *restart_handler_get_by_name(const char *name);
+struct restart_handler *restart_handler_get_by_name(const char *name, int flags);
 
 struct device_node;
 
 struct restart_handler {
 	void (*restart)(struct restart_handler *);
 	int priority;
+#define RESTART_FLAG_WARM_BOOTROM	BIT(0)
+	int flags;
 	struct device_node *of_node;
 	const char *name;
 	struct list_head list;