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

[Stefan Wahren <wahrenst@gmx.net>]

Hi Gregor,

Am 03.09.26 um 16:48 schrieb 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.
sorry for the delay.

Do you know the consequences in case the firmware doesn't support 
RPI_FIRMWARE_SET_REBOOT_FLAGS ?

Best regards
>
> 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@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,
>