ionic: fix completion descriptor access with 2x desc size

The old ionic_rx_service() and ionic_tx_service() used array
indexing to access completion descriptors:

    comp = &((struct ionic_rxq_comp *)cq->base)[cq->tail_idx];

This assumes the stride is sizeof(struct ionic_rxq_comp) = 16 bytes.
However, when the IONIC_Q_F_2X_CQ_DESC flag is set, the actual
completion descriptor size is 32 bytes (2 * sizeof(comp)), and the
completion itself is located at the end of that 32-byte slot. Array
indexing with a 16-byte stride would access the wrong offset.

Use pointer arithmetic that accounts for the actual descriptor size
from cq->desc_size:

    comp = cq->base +
           cq->desc_size * cq->tail_idx +
           cq->desc_size - sizeof(*comp);

This correctly calculates the completion location regardless of
descriptor size. For the common case where desc_size equals
sizeof(*comp), use array indexing in a likely() fast path to avoid
performance regression.

Fixes: 65e548f6b0ff ("ionic: remove the cq_info to save more memory")
Signed-off-by: Prabu Thayalan <prabu.ponrajthayalan@amd.com>
Signed-off-by: Eric Joyner <eric.joyner@amd.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260811195039.1315045-3-eric.joyner@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions