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 | 25 ++++++++++++++++++----- 1 file changed, 20 insertions(+), 5 deletions(-) diff --git a/Documentation/admin-guide/thunderbolt.rst b/Documentation/admin-guide/thunderbolt.rst index 898ad78f3cc7..f44c77860870 100644 --- a/Documentation/admin-guide/thunderbolt.rst +++ b/Documentation/admin-guide/thunderbolt.rst @@ -1,6 +1,23 @@ -============= - Thunderbolt -============= +====================== + Thunderbolt and USB4 +====================== +USB4 is a public spec based on 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 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. @@ -18,8 +35,6 @@ 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
