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Similar to the port-based default priority, IEEE 802.1Q-2018 allows the Application Priority Table to define QoS classes (0 to 7) per IP DSCP value (0 to 63). In the absence of an app table entry for a packet with DSCP value X, QoS classification for that packet falls back to other methods (VLAN PCP or port-based default). The presence of an app table for DSCP value X with priority Y makes the hardware classify the packet to QoS class Y. As opposed to the default-prio where DSA exposes only a "set" in dsa_switch_ops (because the port-based default is the fallback, it always exists, either implicitly or explicitly), for DSCP priorities we expose an "add" and a "del". The addition of a DSCP entry means trusting that DSCP priority, the deletion means ignoring it. Drivers that already trust (at least some) DSCP values can describe their configuration in dsa_switch_ops :: port_get_dscp_prio(), which is called for each DSCP value from 0 to 63. Again, there can be more than one dcbnl app table entry for the same DSCP value, DSA chooses the one with the largest configured priority. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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.