IPQ8074 HW supports three TCL rings for tx. Currently these rings
are mapped based on the Access categories, viz. VO, VI, BE, BK.
In case, one of the traffic type dominates, then it could stress
the same tcl rings. Rather, it would be optimal to make use of all
the rings in a round robin fashion irrespective of the traffic type
so that the load could be evenly distributed among all the rings.
Also, in case the selected ring is busy or full, a retry mechanism
is used to ensure other available ring is selected without dropping
the packet.

In SMP systems, this change avoids a single CPU from getting hogged
when heavy traffic of same category is transmitted.
The tx completion interrupts corresponding to the used tcl ring
would be more which causes the assigned CPU to get hogged.
Distribution of tx packets to different tcl rings helps balance
this load.
Signed-off-by: Sriram R <srirrama@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1586782622-22570-1-git-send-email-srirrama@codeaurora.org