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USB4 v2 spec defines a Gen 4 link that can operate as an asymmetric
120/40G. When the link is asymmetric, the USB4 port on one side of the
link operates with three TX lanes and one RX lane, while the USB4 port
on the opposite side of the link operates with three RX lanes and one TX
lane. Using asymmetric link we can get much more bandwidth from one
direction and that allows us to support the new Ultra High Bit Rate
DisplayPort modes (that consume up to 77.37 Gb/s).
Add the basic logic for changing Gen 4 links to asymmetric and back
following the below rules:
1) The default threshold is 45 Gb/s (tunable by asym_threshold)
2) When DisplayPort tunnel is established, or when there is bandwidth
request through bandwidth allocation mode, the links can be
transitioned to asymmetric or symmetric (depending on the
required bandwidth).
3) Only DisplayPort bandwidth on a link, is taken into account when
deciding whether a link is transitioned to asymmetric or symmetric
4) If bandwidth on a link is >= asym_threshold transition the link to
asymmetric
5) If bandwidth on a link < asym_threshold transition the link to
symmetric (unless the bandwidth request is above currently
allocated on a tunnel).
6) If a USB4 v2 device router with symmetric link is connected,
transition all the links above it to symmetric if the bandwidth
allows.
Signed-off-by: Gil Fine <gil.fine@linux.intel.com>
Co-developed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.