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Support for ENA NETMAP Rx
Needs ReviewPublic

Authored by on Tue, Oct 8, 8:22 AM.



Most of code used for Rx ring initialization could be reused in NETMAP.
Reset of NETMAP ring and new alloc method was added. Driver decides if
use kernels mbufs or NETMAPs slots based on IFCAP_NETMAP flag. It
allows to reuse ena_refill_rx_bufs, which provides proper handling of
Rx out of order completion.

ena_netmap_alloc_rx_slot takes exactly the same arguments as
ena_alloc_rx_mbuf, but instead of allocating one mbuf it takes one slot
from NETMAP ring. Based on queue id proper netmap_ring is found. As
NETMAP provides the "partial opening" feature not all of the rings are
avaiable. Not used points to invalid ring. If there is available slot,
it is taken from the ring. Its buffer is mapped to DMA and its index is
stored in ena_rx_buffer field in ena_rx_buffer structure. Then ena_buf
is filled with addresses and ring state is updated.

Cleanup is handled by ena_netmap_free_rx_slot. It unmaps DMA and returns
buffer to ring. As we could not return more bufs than we have taken and
we should not override occupied slots, buf_index should be 0. It is
being checked by assertion.

ena_netmap_rxsync callback puts received packets back to NETMAP ring and
passes them to user space by updating ring pointers. First it fills
Then it performs two actions:

  • ena_netmap_rx_frames moves received frames from NIC to NETMAP ring,
  • ena_netmap_rx_cleanup fills NIC ring with slots released by userspace


In case of Rx error that could be handled by NIC driver (for example by
performing reset) rx sync should return 0.

ena_netmap_rx_frames first checks if NETMAP ring is in consistent
state and then in the loop receives new frames. When all available
frames are taken nr_hwtail is updated.

Receiving one frame is handled by ena_netmap_rx_frame. If no error
occurrs, each Descriptor is loaded by ena_netmap_rx_load_desc function.
If packets take more than one segments NS_MOREFRAG flag must be set in
all, but not last slot. In case of wrong req_id packet is removed from
NETMAP ring. If packet is successful received counters are updated.

Refiling of NIC ring is performed by ena_netmap_rx_cleanup function.
It calculates number of available slots and call ena_refill_rx_bufs with
proper number.

Submitted by: Rafal Kozik <>

Michal Krawczyk <>

Obtained from: Semihalf
Sponsored by: Amazon, Inc.

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