[PATCH v3 3/4] firmware: raspberrypi: Add reboot mode support

[Gregor Herburger]

The Raspberry Pi firmware has a tryboot mode where it tries to boot from
another partition. This can be used to create a A/B update scheme.

To enable this on the next boot, the RPI_FIRMWARE_SET_REBOOT_FLAGS
message must be sent to the firmware. Add support for this by
registering a reboot mode driver.

Furthermore, safely registering the reboot mode requires adjusting the
teardown sequence. Replace the manually called rpi_firmware_put() with a
devres-managed called (devm_add_action_or_reset). Without this, the
cleanup function of devm_reboot_mode_register() would trigger a
use-after-free error by attempting to access the firmware context after
it had already been freed by rpi_firmware_remove().

Signed-off-by: Gregor Herburger <gregor.herburger at linutronix.de>
---
 drivers/firmware/Kconfig                   |  2 ++
 drivers/firmware/raspberrypi.c             | 40 ++++++++++++++++++++++++++----
 include/soc/bcm2835/raspberrypi-firmware.h |  2 ++
 3 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index bbd2155d84838..34605bf7c9734 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -115,6 +115,8 @@ config ISCSI_IBFT
 config RASPBERRYPI_FIRMWARE
 	tristate "Raspberry Pi Firmware Driver"
 	depends on BCM2835_MBOX
+	select POWER_RESET
+	select REBOOT_MODE
 	help
 	  This option enables support for communicating with the firmware on the
 	  Raspberry Pi.
diff --git a/drivers/firmware/raspberrypi.c b/drivers/firmware/raspberrypi.c
index 0aa322e9a2e73..2a0c40b8052e5 100644
--- a/drivers/firmware/raspberrypi.c
+++ b/drivers/firmware/raspberrypi.c
@@ -14,6 +14,7 @@
 #include <linux/of.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/reboot-mode.h>
 #include <linux/slab.h>
 #include <soc/bcm2835/raspberrypi-firmware.h>
 
@@ -29,6 +30,7 @@ struct rpi_firmware {
 	struct mbox_client cl;
 	struct mbox_chan *chan; /* The property channel. */
 	struct completion c;
+	struct reboot_mode_driver reboot_mode;
 	u32 enabled;
 
 	struct kref consumers;
@@ -273,10 +275,37 @@ static void devm_rpi_firmware_put(void *data)
 	rpi_firmware_put(fw);
 }
 
+static int rpi_firmware_reboot_mode_write(struct reboot_mode_driver *reboot,
+					  unsigned int magic)
+{
+	struct rpi_firmware *fw = container_of(reboot, struct rpi_firmware,
+					       reboot_mode);
+	__le32 fw_magic = cpu_to_le32(magic);
+
+	if (!magic)
+		return 0;
+
+	return rpi_firmware_property(fw, RPI_FIRMWARE_SET_REBOOT_FLAGS,
+				     &fw_magic, sizeof(fw_magic));
+}
+
+static void rpi_register_reboot_mode(struct device *dev, struct rpi_firmware *fw)
+{
+	int ret;
+
+	fw->reboot_mode.dev = dev;
+	fw->reboot_mode.write = rpi_firmware_reboot_mode_write;
+	ret = devm_reboot_mode_register(dev, &fw->reboot_mode);
+	if (ret)
+		dev_err(dev, "Failed to register reboot mode: %d\n", ret);
+
+}
+
 static int rpi_firmware_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct rpi_firmware *fw;
+	int ret;
 
 	/*
 	 * Memory will be freed by rpi_firmware_delete() once all users have
@@ -292,7 +321,7 @@ static int rpi_firmware_probe(struct platform_device *pdev)
 
 	fw->chan = mbox_request_channel(&fw->cl, 0);
 	if (IS_ERR(fw->chan)) {
-		int ret = PTR_ERR(fw->chan);
+		ret = PTR_ERR(fw->chan);
 		kfree(fw);
 		return dev_err_probe(dev, ret, "Failed to get mbox channel\n");
 	}
@@ -302,9 +331,14 @@ static int rpi_firmware_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, fw);
 
+	ret = devm_add_action_or_reset(dev, devm_rpi_firmware_put, fw);
+	if (ret)
+		return ret;
+
 	rpi_firmware_print_firmware_revision(fw);
 	rpi_register_hwmon_driver(dev, fw);
 	rpi_register_clk_driver(dev);
+	rpi_register_reboot_mode(dev, fw);
 
 	return 0;
 }
@@ -321,14 +355,10 @@ static void rpi_firmware_shutdown(struct platform_device *pdev)
 
 static void rpi_firmware_remove(struct platform_device *pdev)
 {
-	struct rpi_firmware *fw = platform_get_drvdata(pdev);
-
 	platform_device_unregister(rpi_hwmon);
 	rpi_hwmon = NULL;
 	platform_device_unregister(rpi_clk);
 	rpi_clk = NULL;
-
-	rpi_firmware_put(fw);
 }
 
 static const struct of_device_id rpi_firmware_of_match[] = {
diff --git a/include/soc/bcm2835/raspberrypi-firmware.h b/include/soc/bcm2835/raspberrypi-firmware.h
index 66cc5a426c3c5..f905bff0fb3ea 100644
--- a/include/soc/bcm2835/raspberrypi-firmware.h
+++ b/include/soc/bcm2835/raspberrypi-firmware.h
@@ -81,6 +81,7 @@ enum rpi_firmware_property_tag {
 	RPI_FIRMWARE_GET_POE_HAT_VAL =                        0x00030049,
 	RPI_FIRMWARE_SET_POE_HAT_VAL =                        0x00030050,
 	RPI_FIRMWARE_NOTIFY_XHCI_RESET =                      0x00030058,
+	RPI_FIRMWARE_GET_REBOOT_FLAGS =                       0x00030064,
 	RPI_FIRMWARE_NOTIFY_DISPLAY_DONE =                    0x00030066,
 	RPI_FIRMWARE_SET_CLOCK_STATE =                        0x00038001,
 	RPI_FIRMWARE_SET_CLOCK_RATE =                         0x00038002,
@@ -92,6 +93,7 @@ enum rpi_firmware_property_tag {
 	RPI_FIRMWARE_SET_SDHOST_CLOCK =                       0x00038042,
 	RPI_FIRMWARE_SET_GPIO_CONFIG =                        0x00038043,
 	RPI_FIRMWARE_SET_PERIPH_REG =                         0x00038045,
+	RPI_FIRMWARE_SET_REBOOT_FLAGS =                       0x00038064,
 
 	/* Dispmanx TAGS */
 	RPI_FIRMWARE_FRAMEBUFFER_ALLOCATE =                   0x00040001,

-- 
2.47.3