enic: add admin CQ service with MSI-X interrupt and workqueue polling

Add completion queue (CQ) service for the admin channel work queue
(WQ) and receive queue (RQ), driven by a dedicated MSI-X interrupt
and a workqueue-based CQ poller.

The admin WQ CQ service advances the completion ring and returns the
number of descriptors consumed.  The admin RQ CQ service does the
same for receive completions and copies each received message out of
its pre-posted DMA buffer into a dynamically allocated queue entry.
The pending queue is bounded to ENIC_ADMIN_MSG_MAX (256) entries so a
buggy or hostile VF cannot drive the host out of memory; messages are
enqueued for deferred dispatch by a separate work_struct so the CQ
poller stays short.

When the MSI-X interrupt fires, the ISR schedules the CQ poll work.
The work handler drains all pending completions, kicks message
dispatch if work was done, and returns credits to unmask the
interrupt.  The admin vector is kept masked from the time the IRQ is
requested until the rings are initialised and filled during channel
open, so an early or spurious interrupt cannot run the poll handler
against uninitialised rings.

The poll handler snapshots the pending credit count before draining
the CQ so it acknowledges exactly what the hardware reported for this
interrupt; any credits that accrue during draining are serviced by the
next interrupt.  The credit write also sets the mask bit to re-arm the
vector, and that unmask is applied independently of the credit count,
so the vector is re-armed even when zero credits are returned -- which
matters here because the admin channel is not re-polled like the NAPI
data path.

If an admin RQ buffer refill fails under transient memory pressure,
reschedule the CQ poll work itself after a short delay to retry the
refill and re-arm the RQ, so the admin channel cannot stall when the
ring would otherwise be left empty with no completion to drive the
next refill.  The poll work is a delayed_work for this reason; routing
the retry through it keeps the admin RQ ring owned by a single context
so refills never run concurrently.

Signed-off-by: Satish Kharat <satishkh@cisco.com>
Link: https://patch.msgid.link/20260812-enic-sriov-v2-admin-channel-v2-v13-4-b3809e448aba@cisco.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions