On Mon, Mar 19, 2018 at 10:47:48PM -0400, Sinan Kaya wrote:
> Code includes wmb() followed by writel() in multiple places. writel()
> already has a barrier on some architectures like arm64.
>
> This ends up CPU observing two barriers back to back before executing the
> register write.
>
> Since code already has an explicit barrier call, changing writel() to
> writel_relaxed().
>
> Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> drivers/infiniband/hw/qedr/verbs.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/hw/qedr/verbs.c b/drivers/infiniband/hw/qedr/verbs.c
> index ccd55f4..db60360 100644
> +++ b/drivers/infiniband/hw/qedr/verbs.c
> @@ -860,7 +860,7 @@ static void doorbell_cq(struct qedr_cq *cq, u32 cons, u8 flags)
> wmb();
> cq->db.data.agg_flags = flags;
> cq->db.data.value = cpu_to_le32(cons);
> - writeq(cq->db.raw, cq->db_addr);
> + writeq_relaxed(cq->db.raw, cq->db_addr);
>
> /* Make sure write would stick */
> mmiowb();
> @@ -3338,7 +3338,7 @@ int qedr_post_recv(struct ib_qp *ibqp, struct ib_recv_wr *wr,
>
> qp->rq.db_data.data.value++;
>
> - writel(qp->rq.db_data.raw, qp->rq.db);
> + writel_relaxed(qp->rq.db_data.raw, qp->rq.db);
>
> /* Make sure write sticks */
> mmiowb();
Looks fine, but the next lines should be relaxed too:
/* Make sure write sticks */
mmiowb();
if (rdma_protocol_iwarp(&dev->ibdev, 1)) {
writel(qp->rq.iwarp_db2_data.raw, qp->rq.iwarp_db2);
mmiowb(); /* for second doorbell */
}
mmiowb() is strong enough to order writel, IIRC.
Jason
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