Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.. SPDX-License-Identifier: GPL-2.0
+
+======================
+ USB4 and Thunderbolt
+======================
+USB4 is the public specification based on Thunderbolt 3 protocol with
+some differences at the register level among other things. Connection
+manager is an entity running on the host router (host controller)
+responsible for enumerating routers and establishing tunnels. A
+connection manager can be implemented either in firmware or software.
+Typically PCs come with a firmware connection manager for Thunderbolt 3
+and early USB4 capable systems. Apple systems on the other hand use
+software connection manager and the later USB4 compliant devices follow
+the suit.
+
+The Linux Thunderbolt driver supports both and can detect at runtime which
+connection manager implementation is to be used. To be on the safe side the
+software connection manager in Linux also advertises security level
+``user`` which means PCIe tunneling is disabled by default. The
+documentation below applies to both implementations with the exception that
+the software connection manager only supports ``user`` security level and
+is expected to be accompanied with an IOMMU based DMA protection.
+
+Security levels and how to use them
+-----------------------------------
+The interface presented here is not meant for end users. Instead there
+should be a userspace tool that handles all the low-level details, keeps
+a database of the authorized devices and prompts users for new connections.
+
+More details about the sysfs interface for Thunderbolt devices can be
+found in ``Documentation/ABI/testing/sysfs-bus-thunderbolt``.
+
+Those users who just want to connect any device without any sort of
+manual work can add following line to
+``/etc/udev/rules.d/99-local.rules``::
+
+  ACTION=="add", SUBSYSTEM=="thunderbolt", ATTR{authorized}=="0", ATTR{authorized}="1"
+
+This will authorize all devices automatically when they appear. However,
+keep in mind that this bypasses the security levels and makes the system
+vulnerable to DMA attacks.
+
+Starting with Intel Falcon Ridge Thunderbolt controller there are 4
+security levels available. Intel Titan Ridge added one more security level
+(usbonly). The reason for these is the fact that the connected devices can
+be DMA masters and thus read contents of the host memory without CPU and OS
+knowing about it. There are ways to prevent this by setting up an IOMMU but
+it is not always available for various reasons.
+
+The security levels are as follows:
+
+  none
+    All devices are automatically connected by the firmware. No user
+    approval is needed. In BIOS settings this is typically called
+    *Legacy mode*.
+
+  user
+    User is asked whether the device is allowed to be connected.
+    Based on the device identification information available through
+    ``/sys/bus/thunderbolt/devices``, the user then can make the decision.
+    In BIOS settings this is typically called *Unique ID*.
+
+  secure
+    User is asked whether the device is allowed to be connected. In
+    addition to UUID the device (if it supports secure connect) is sent
+    a challenge that should match the expected one based on a random key
+    written to the ``key`` sysfs attribute. In BIOS settings this is
+    typically called *One time saved key*.
+
+  dponly
+    The firmware automatically creates tunnels for Display Port and
+    USB. No PCIe tunneling is done. In BIOS settings this is
+    typically called *Display Port Only*.
+
+  usbonly
+    The firmware automatically creates tunnels for the USB controller and
+    Display Port in a dock. All PCIe links downstream of the dock are
+    removed.
+
+The current security level can be read from
+``/sys/bus/thunderbolt/devices/domainX/security`` where ``domainX`` is
+the Thunderbolt domain the host controller manages. There is typically
+one domain per Thunderbolt host controller.
+
+If the security level reads as ``user`` or ``secure`` the connected
+device must be authorized by the user before PCIe tunnels are created
+(e.g the PCIe device appears).
+
+Each Thunderbolt device plugged in will appear in sysfs under
+``/sys/bus/thunderbolt/devices``. The device directory carries
+information that can be used to identify the particular device,
+including its name and UUID.
+
+Authorizing devices when security level is ``user`` or ``secure``
+-----------------------------------------------------------------
+When a device is plugged in it will appear in sysfs as follows::
+
+  /sys/bus/thunderbolt/devices/0-1/authorized	- 0
+  /sys/bus/thunderbolt/devices/0-1/device	- 0x8004
+  /sys/bus/thunderbolt/devices/0-1/device_name	- Thunderbolt to FireWire Adapter
+  /sys/bus/thunderbolt/devices/0-1/vendor	- 0x1
+  /sys/bus/thunderbolt/devices/0-1/vendor_name	- Apple, Inc.
+  /sys/bus/thunderbolt/devices/0-1/unique_id	- e0376f00-0300-0100-ffff-ffffffffffff
+
+The ``authorized`` attribute reads 0 which means no PCIe tunnels are
+created yet. The user can authorize the device by simply entering::
+
+  # echo 1 > /sys/bus/thunderbolt/devices/0-1/authorized
+
+This will create the PCIe tunnels and the device is now connected.
+
+If the device supports secure connect, and the domain security level is
+set to ``secure``, it has an additional attribute ``key`` which can hold
+a random 32-byte value used for authorization and challenging the device in
+future connects::
+
+  /sys/bus/thunderbolt/devices/0-3/authorized	- 0
+  /sys/bus/thunderbolt/devices/0-3/device	- 0x305
+  /sys/bus/thunderbolt/devices/0-3/device_name	- AKiTiO Thunder3 PCIe Box
+  /sys/bus/thunderbolt/devices/0-3/key		-
+  /sys/bus/thunderbolt/devices/0-3/vendor	- 0x41
+  /sys/bus/thunderbolt/devices/0-3/vendor_name	- inXtron
+  /sys/bus/thunderbolt/devices/0-3/unique_id	- dc010000-0000-8508-a22d-32ca6421cb16
+
+Notice the key is empty by default.
+
+If the user does not want to use secure connect they can just ``echo 1``
+to the ``authorized`` attribute and the PCIe tunnels will be created in
+the same way as in the ``user`` security level.
+
+If the user wants to use secure connect, the first time the device is
+plugged a key needs to be created and sent to the device::
+
+  # key=$(openssl rand -hex 32)
+  # echo $key > /sys/bus/thunderbolt/devices/0-3/key
+  # echo 1 > /sys/bus/thunderbolt/devices/0-3/authorized
+
+Now the device is connected (PCIe tunnels are created) and in addition
+the key is stored on the device NVM.
+
+Next time the device is plugged in the user can verify (challenge) the
+device using the same key::
+
+  # echo $key > /sys/bus/thunderbolt/devices/0-3/key
+  # echo 2 > /sys/bus/thunderbolt/devices/0-3/authorized
+
+If the challenge the device returns back matches the one we expect based
+on the key, the device is connected and the PCIe tunnels are created.
+However, if the challenge fails no tunnels are created and error is
+returned to the user.
+
+If the user still wants to connect the device they can either approve
+the device without a key or write a new key and write 1 to the
+``authorized`` file to get the new key stored on the device NVM.
+
+DMA protection utilizing IOMMU
+------------------------------
+Recent systems from 2018 and forward with Thunderbolt ports may natively
+support IOMMU. This means that Thunderbolt security is handled by an IOMMU
+so connected devices cannot access memory regions outside of what is
+allocated for them by drivers. When Linux is running on such system it
+automatically enables IOMMU if not enabled by the user already. These
+systems can be identified by reading ``1`` from
+``/sys/bus/thunderbolt/devices/domainX/iommu_dma_protection`` attribute.
+
+The driver does not do anything special in this case but because DMA
+protection is handled by the IOMMU, security levels (if set) are
+redundant. For this reason some systems ship with security level set to
+``none``. Other systems have security level set to ``user`` in order to
+support downgrade to older OS, so users who want to automatically
+authorize devices when IOMMU DMA protection is enabled can use the
+following ``udev`` rule::
+
+  ACTION=="add", SUBSYSTEM=="thunderbolt", ATTRS{iommu_dma_protection}=="1", ATTR{authorized}=="0", ATTR{authorized}="1"
+
+Upgrading NVM on Thunderbolt device, host or retimer
+----------------------------------------------------
+Since most of the functionality is handled in firmware running on a
+host controller or a device, it is important that the firmware can be
+upgraded to the latest where possible bugs in it have been fixed.
+Typically OEMs provide this firmware from their support site.
+
+There is also a central site which has links where to download firmware
+for some machines:
+
+  `Thunderbolt Updates <https://thunderbolttechnology.net/updates>`_
+
+Before you upgrade firmware on a device, host or retimer, please make
+sure it is a suitable upgrade. Failing to do that may render the device
+in a state where it cannot be used properly anymore without special
+tools!
+
+Host NVM upgrade on Apple Macs is not supported.
+
+Once the NVM image has been downloaded, you need to plug in a
+Thunderbolt device so that the host controller appears. It does not
+matter which device is connected (unless you are upgrading NVM on a
+device - then you need to connect that particular device).
+
+Note an OEM-specific method to power the controller up ("force power") may
+be available for your system in which case there is no need to plug in a
+Thunderbolt device.
+
+After that we can write the firmware to the non-active parts of the NVM
+of the host or device. As an example here is how Intel NUC6i7KYK (Skull
+Canyon) Thunderbolt controller NVM is upgraded::
+
+  # dd if=KYK_TBT_FW_0018.bin of=/sys/bus/thunderbolt/devices/0-0/nvm_non_active0/nvmem
+
+Once the operation completes we can trigger NVM authentication and
+upgrade process as follows::
+
+  # echo 1 > /sys/bus/thunderbolt/devices/0-0/nvm_authenticate
+
+If no errors are returned, the host controller shortly disappears. Once
+it comes back the driver notices it and initiates a full power cycle.
+After a while the host controller appears again and this time it should
+be fully functional.
+
+We can verify that the new NVM firmware is active by running the following
+commands::
+
+  # cat /sys/bus/thunderbolt/devices/0-0/nvm_authenticate
+  0x0
+  # cat /sys/bus/thunderbolt/devices/0-0/nvm_version
+  18.0
+
+If ``nvm_authenticate`` contains anything other than 0x0 it is the error
+code from the last authentication cycle, which means the authentication
+of the NVM image failed.
+
+Note names of the NVMem devices ``nvm_activeN`` and ``nvm_non_activeN``
+depend on the order they are registered in the NVMem subsystem. N in
+the name is the identifier added by the NVMem subsystem.
+
+Upgrading NVM when host controller is in safe mode
+--------------------------------------------------
+If the existing NVM is not properly authenticated (or is missing) the
+host controller goes into safe mode which means that the only available
+functionality is flashing a new NVM image. When in this mode, reading
+``nvm_version`` fails with ``ENODATA`` and the device identification
+information is missing.
+
+To recover from this mode, one needs to flash a valid NVM image to the
+host controller in the same way it is done in the previous chapter.
+
+Networking over Thunderbolt cable
+---------------------------------
+Thunderbolt technology allows software communication between two hosts
+connected by a Thunderbolt cable.
+
+It is possible to tunnel any kind of traffic over a Thunderbolt link but
+currently we only support Apple ThunderboltIP protocol.
+
+If the other host is running Windows or macOS, the only thing you need to
+do is to connect a Thunderbolt cable between the two hosts; the
+``thunderbolt-net`` driver is loaded automatically. If the other host is
+also Linux you should load ``thunderbolt-net`` manually on one host (it
+does not matter which one)::
+
+  # modprobe thunderbolt-net
+
+This triggers module load on the other host automatically. If the driver
+is built-in to the kernel image, there is no need to do anything.
+
+The driver will create one virtual ethernet interface per Thunderbolt
+port which are named like ``thunderbolt0`` and so on. From this point
+you can either use standard userspace tools like ``ifconfig`` to
+configure the interface or let your GUI handle it automatically.
+
+Forcing power
+-------------
+Many OEMs include a method that can be used to force the power of a
+Thunderbolt controller to an "On" state even if nothing is connected.
+If supported by your machine this will be exposed by the WMI bus with
+a sysfs attribute called "force_power".
+
+For example the intel-wmi-thunderbolt driver exposes this attribute in:
+  /sys/bus/wmi/devices/86CCFD48-205E-4A77-9C48-2021CBEDE341/force_power
+
+  To force the power to on, write 1 to this attribute file.
+  To disable force power, write 0 to this attribute file.
+
+Note: it's currently not possible to query the force power state of a platform.