Re: [PATCH net v2] net: mana: Ring doorbell at 4 CQ wraparounds

Vadim Fedorenko
2026-02-27T10:53:22Z

On 26/02/2026 19:28, Long Li wrote:
> MANA hardware requires at least one doorbell ring every 8 wraparounds
> of the CQ. The driver rings the doorbell as a form of flow control to
> inform hardware that CQEs have been consumed.
>
> The NAPI poll functions mana_poll_tx_cq() and mana_poll_rx_cq() can
> poll up to CQE_POLLING_BUFFER (512) completions per call. If the CQ
> has fewer than 512 entries, a single poll call can process more than
> 4 wraparounds without ringing the doorbell. The doorbell threshold
> check also uses ">" instead of ">=", delaying the ring by one extra
> CQE beyond 4 wraparounds. Combined, these issues can cause the driver
> to exceed the 8-wraparound hardware limit, leading to missed
> completions and stalled queues.
>
> Fix this by capping the number of CQEs polled per call to 4 wraparounds
> of the CQ in both TX and RX paths. Also change the doorbell threshold
> from ">" to ">=" so the doorbell is rung as soon as 4 wraparounds are
> reached.
>
> Cc: stable@vger.kernel.org
> Fixes: 58a63729c957 ("net: mana: Fix doorbell out of order violation and avoid unnecessary doorbell rings")
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
> v2: Use min() instead of min_t(u32, ...) since queue_size is already u32
> drivers/net/ethernet/microsoft/mana/mana_en.c | 23 +++++++++++++++----
> 1 file changed, 18 insertions(+), 5 deletions(-)

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>