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    SubjectRe: [PATCH net-next 2/3] net: hns3: add support for TX push mode
    On Tue, Jun 22, 2021 at 07:11:10PM +0800, Guangbin Huang wrote:
    > From: Huazhong Tan <tanhuazhong@huawei.com>
    >
    > For the device that supports the TX push capability, the BD can
    > be directly copied to the device memory. However, due to hardware
    > restrictions, the push mode can be used only when there are no
    > more than two BDs, otherwise, the doorbell mode based on device
    > memory is used.
    >
    > Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
    > Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
    > ---
    > drivers/net/ethernet/hisilicon/hns3/hnae3.h | 1 +
    > drivers/net/ethernet/hisilicon/hns3/hns3_enet.c | 83 ++++++++++++++++++++--
    > drivers/net/ethernet/hisilicon/hns3/hns3_enet.h | 6 ++
    > drivers/net/ethernet/hisilicon/hns3/hns3_ethtool.c | 2 +
    > .../net/ethernet/hisilicon/hns3/hns3pf/hclge_cmd.c | 2 +
    > .../ethernet/hisilicon/hns3/hns3pf/hclge_main.c | 11 ++-
    > .../ethernet/hisilicon/hns3/hns3pf/hclge_main.h | 8 +++
    > .../ethernet/hisilicon/hns3/hns3vf/hclgevf_cmd.c | 2 +
    > .../ethernet/hisilicon/hns3/hns3vf/hclgevf_main.c | 11 ++-
    > .../ethernet/hisilicon/hns3/hns3vf/hclgevf_main.h | 8 +++
    > 10 files changed, 126 insertions(+), 8 deletions(-)
    >
    > diff --git a/drivers/net/ethernet/hisilicon/hns3/hnae3.h b/drivers/net/ethernet/hisilicon/hns3/hnae3.h
    > index 0b202f4def83..3979d5d2e842 100644
    > --- a/drivers/net/ethernet/hisilicon/hns3/hnae3.h
    > +++ b/drivers/net/ethernet/hisilicon/hns3/hnae3.h
    > @@ -163,6 +163,7 @@ struct hnae3_handle;
    >
    > struct hnae3_queue {
    > void __iomem *io_base;
    > + void __iomem *mem_base;
    > struct hnae3_ae_algo *ae_algo;
    > struct hnae3_handle *handle;
    > int tqp_index; /* index in a handle */
    > diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
    > index cdb5f14fb6bc..8649bd8e1b57 100644
    > --- a/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
    > +++ b/drivers/net/ethernet/hisilicon/hns3/hns3_enet.c
    > @@ -2002,9 +2002,77 @@ static int hns3_fill_skb_to_desc(struct hns3_enet_ring *ring,
    > return bd_num;
    > }
    >
    > +static void hns3_tx_push_bd(struct hns3_enet_ring *ring, int num)
    > +{
    > +#define HNS3_BYTES_PER_64BIT 8
    > +
    > + struct hns3_desc desc[HNS3_MAX_PUSH_BD_NUM] = {};
    > + int offset = 0;
    > +
    > + /* make sure everything is visible to device before
    > + * excuting tx push or updating doorbell
    > + */
    > + dma_wmb();
    > +
    > + do {
    > + int idx = (ring->next_to_use - num + ring->desc_num) %
    > + ring->desc_num;
    > +
    > + u64_stats_update_begin(&ring->syncp);
    > + ring->stats.tx_push++;
    > + u64_stats_update_end(&ring->syncp);
    > + memcpy(&desc[offset], &ring->desc[idx],
    > + sizeof(struct hns3_desc));
    > + offset++;
    > + } while (--num);
    > +
    > + __iowrite64_copy(ring->tqp->mem_base, desc,
    > + (sizeof(struct hns3_desc) * HNS3_MAX_PUSH_BD_NUM) /
    > + HNS3_BYTES_PER_64BIT);
    > +
    > +#if defined(CONFIG_ARM64)
    > + dgh();
    > +#endif

    It looks a bit weird putting this at the end of the function, given that
    it's supposed to do something to a pair of accesses. Please can you explain
    what it's doing, and also provide some numbers to show that it's worthwhile
    (given that it's a performance hint not a correctness thing afaict).

    > +}
    > +
    > +static void hns3_tx_mem_doorbell(struct hns3_enet_ring *ring)
    > +{
    > +#define HNS3_MEM_DOORBELL_OFFSET 64
    > +
    > + __le64 bd_num = cpu_to_le64((u64)ring->pending_buf);
    > +
    > + /* make sure everything is visible to device before
    > + * excuting tx push or updating doorbell
    > + */
    > + dma_wmb();
    > +
    > + __iowrite64_copy(ring->tqp->mem_base + HNS3_MEM_DOORBELL_OFFSET,
    > + &bd_num, 1);
    > + u64_stats_update_begin(&ring->syncp);
    > + ring->stats.tx_mem_doorbell += ring->pending_buf;
    > + u64_stats_update_end(&ring->syncp);
    > +
    > +#if defined(CONFIG_ARM64)
    > + dgh();
    > +#endif

    Same here.

    Thanks,

    Will

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