Re: [PATCH v2] usb: acpi: fix boot hang due to early incorrect 'tunneled' USB3 device links

[Mario Limonciello <mario.limonciello@amd.com>]

On 10/24/2024 08:13, Mathias Nyman wrote:
> Fix a boot hang issue triggered when a USB3 device is incorrectly assumed
> to be tunneled over USB4, thus attempting to create a device link between
> the USB3 "consumer" device and the USB4 "supplier" Host Interface before
> the USB4 side is properly bound to a driver.
> 
> This could happen if xhci isn't capable of detecting tunneled devices,
> but ACPI tables contain all info needed to assume device is tunneled.
> i.e. udev->tunnel_mode == USB_LINK_UNKNOWN.
> 
> It turns out that even for actual tunneled USB3 devices it can't be
> assumed that the thunderbolt driver providing the tunnel is loaded
> before the tunneled USB3 device is created.
> The tunnel can be created by BIOS and remain in use by thunderbolt/USB4
> host driver once it loads.
> 
> Solve this by making the device link "stateless", which doesn't create
> a driver presence order dependency between the supplier and consumer
> drivers.
> It still guarantees correct suspend/resume and shutdown ordering.
> 
> cc: Mario Limonciello <mario.limonciello@amd.com>
> Fixes: f1bfb4a6fed6 ("usb: acpi: add device link between tunneled USB3 device and USB4 Host Interface")
> Tested-by: Harry Wentland <harry.wentland@amd.com>
Tested-by: Mario Limonciello <mario.limonciello@amd.com>
> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
> ---
>   v2: Use stateless device link instead of checking if driver is bound
> 
>   drivers/usb/core/usb-acpi.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/core/usb-acpi.c b/drivers/usb/core/usb-acpi.c
> index 21585ed89ef8..03c22114214b 100644
> --- a/drivers/usb/core/usb-acpi.c
> +++ b/drivers/usb/core/usb-acpi.c
> @@ -170,11 +170,11 @@ static int usb_acpi_add_usb4_devlink(struct usb_device *udev)
>   	struct fwnode_handle *nhi_fwnode __free(fwnode_handle) =
>   		fwnode_find_reference(dev_fwnode(&port_dev->dev), "usb4-host-interface", 0);
>   
> -	if (IS_ERR(nhi_fwnode))
> +	if (IS_ERR(nhi_fwnode) || !nhi_fwnode->dev)
>   		return 0;
>   
>   	link = device_link_add(&port_dev->child->dev, nhi_fwnode->dev,
> -			       DL_FLAG_AUTOREMOVE_CONSUMER |
> +			       DL_FLAG_STATELESS |
>   			       DL_FLAG_RPM_ACTIVE |
>   			       DL_FLAG_PM_RUNTIME);
>   	if (!link) {