daisy chained thunderbolt devices not working at reboot on AMD strix platforms

[You-Sheng Yang]

[SRU Justification]

[Impact]

Devices on PCIe bus on some AMD based systems may not function normally.

Boot firmware (typically BIOS) might have created tunnels of its own. The tunnel configuration that it does might be sub-optimal. For instance it may only support HBR2 monitors so the DisplayPort tunnels it created may limit Linux graphics drivers. In addition there is an issue on some AMD based systems where the BIOS does not allocate enough PCIe resources for future topology extension.

[Fix]

4 commits already in upstream linux repo that resets USB4 v1 routers in addition to already reset v2 routes to align the behavior with Windows Connection Manager.

[Test Case]

On affected platforms with monitor connected across reboots, the DUT reboots into linux with blank screen. This should turn it back to normal as expected.

[Where problems could occur]

No. The reset triggers Linux to re-allocate necessary resources for its own, and this is what Windows does, too.

[Other Info]

While this is in v6.9-rc1 and backported to stable at v6.8.8, Noble and oem-6.8 are nominated.

========== original but report ==========

Boot firmware (typically BIOS) might have created tunnels of its own. The tunnel configuration that it does might be sub-optimal. For instance it may only support HBR2 monitors so the DisplayPort tunnels it created may limit Linux graphics drivers. In addition there is an issue on some AMD based systems where the BIOS does not allocate enough PCIe resources for future topology extension. By resetting the USB4 topology the PCIe links will be reset as well allowing Linux to re-allocate.

This aligns the behavior with Windows Connection Manager.

Fixes merged to linus tree for v6.9-rc1:
* 59a54c5f3dbde thunderbolt: Reset topology created by the boot firmware
* ec8162b3f0683 thunderbolt: Make tb_switch_reset() support Thunderbolt 2, 3 and USB4 routers
* b35c1d7b11da8 thunderbolt: Introduce tb_path_deactivate_hop()
* 01da6b99d49f6 thunderbolt: Introduce tb_port_reset()

[You-Sheng Yang (vicamo)]

SRU:
* https://kernel.ubuntu.com/gitea/kernel/noble-linux-oem/pulls/3 (oem-6.8)