Update user's and administrator's guide to mention USB4, how it relates to Thunderbolt (it is public spec of Thunderbolt 3) and and how it is supported in Linux. Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> --- Documentation/admin-guide/thunderbolt.rst | 27 ++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) diff --git a/Documentation/admin-guide/thunderbolt.rst b/Documentation/admin-guide/thunderbolt.rst index 898ad78f3cc7..4cbed319133d 100644 --- a/Documentation/admin-guide/thunderbolt.rst +++ b/Documentation/admin-guide/thunderbolt.rst @@ -1,6 +1,25 @@ -============= - Thunderbolt -============= +====================== + Thunderbolt and USB4 +====================== +USB4 is the public spec of Thunderbolt 3 with some differences at the +register level among other things. There are two different +implementations available: firmware connection manager and software +connection manager. 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 future USB4 +compliant PCs 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. @@ -18,8 +37,6 @@ 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. -Security levels and how to use them ------------------------------------ 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 -- 2.23.0
