> -----Original Message----- > From: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> > Sent: Tuesday, October 1, 2019 6:38 AM > To: linux-usb@xxxxxxxxxxxxxxx > Cc: Andreas Noever; Michael Jamet; Mika Westerberg; Yehezkel Bernat; Rajmohan > Mani; Nicholas Johnson; Lukas Wunner; Greg Kroah-Hartman; Alan Stern; > Limonciello, Mario; Anthony Wong; linux-kernel@xxxxxxxxxxxxxxx > Subject: [RFC PATCH 21/22] thunderbolt: Update documentation with the USB4 > information > > > [EXTERNAL EMAIL] > > 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. Future isn't going to age very well. Perhaps refer instead to "later" USB4 compliant PCs. Also, we should be seeing this stuff pop-up outside of PCs. So maybe better to just call out "devices". > + > +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
