Re: [PATCH net-next v1 4/8] net: ieee8021q: add tt_to_pcp()

On Fri, Oct 2, 2026 at 1:58 PM Oleksij Rempel [off-list ref] wrote:

Add ieee8021q_tt_to_pcp(), the inverse of ieee8021q_pcp_to_tt(): it
encodes an 802.1Q traffic type back to its Priority Code Point, and
completes the pcp/tt helper family.

A driver that reseeds its PCP classifier through ieee8021q_pcp_to_tt()
stores traffic types in the hardware tables, while the dcbnl priority
ops exchange 802.1p priorities across the DSA boundary. Reading such a
table back therefore needs the reverse mapping to restore the 802.1p
value, which no existing helper provides. Because pcp_to_tt only
transposes Best Effort and Background and is the identity elsewhere the
two directions are numerically equal; provide tt_to_pcp as its own named
function so the read path does not decode a traffic type as if it were a
PCP.

The first user is the Realtek rtl8365mb DSA driver, whose dcbnl
get_default_prio and get_dscp_prio paths read back traffic types and
must return 802.1p priorities.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>

Perfect, this is very helpful stuff.
Reviewed-by: Linus Walleij <linusw@kernel.org>

Yours,
Linus Walleij