[xdp-hints] Re: [PATCH net-next v3 3/4] net: stmmac: add Rx HWTS metadata to XDP receive pkt

["Song, Yoong Siang" <yoong.siang.song@intel.com>]

On Thursday, April 13, 2023 5:46 AM, Stanislav Fomichev <sdf@google.com> wrote:
>On Wed, Apr 12, 2023 at 1:56 PM Jacob Keller <jacob.e.keller@intel.com> wrote:
>>
>>
>>
>> On 4/12/2023 10:00 AM, Stanislav Fomichev wrote:
>> > On 04/12, Song Yoong Siang wrote:
>> >> Add receive hardware timestamp metadata support via kfunc to XDP
>> >> receive packets.
>> >>
>> >> Suggested-by: Stanislav Fomichev <sdf@google.com>
>> >> Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
>> >> ---
>> >>  drivers/net/ethernet/stmicro/stmmac/stmmac.h  |  3 +++
>> >> .../net/ethernet/stmicro/stmmac/stmmac_main.c | 26
>> >> ++++++++++++++++++-
>> >>  2 files changed, 28 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
>> >> b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
>> >> index ac8ccf851708..826ac0ec88c6 100644
>> >> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
>> >> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
>> >> @@ -94,6 +94,9 @@ struct stmmac_rx_buffer {
>> >>
>> >>  struct stmmac_xdp_buff {
>> >>      struct xdp_buff xdp;
>> >> +    struct stmmac_priv *priv;
>> >> +    struct dma_desc *p;
>> >> +    struct dma_desc *np;
>> >>  };
>> >>
>> >>  struct stmmac_rx_queue {
>> >> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> >> b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> >> index f7bbdf04d20c..ed660927b628 100644
>> >> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> >> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> >> @@ -5315,10 +5315,15 @@ static int stmmac_rx(struct stmmac_priv
>> >> *priv, int limit, u32 queue)
>> >>
>> >>                      xdp_init_buff(&ctx.xdp, buf_sz, &rx_q->xdp_rxq);
>> >>                      xdp_prepare_buff(&ctx.xdp, page_address(buf->page),
>> >> -                                     buf->page_offset, buf1_len, false);
>> >> +                                     buf->page_offset, buf1_len,
>> >> + true);
>> >>
>> >>                      pre_len = ctx.xdp.data_end - ctx.xdp.data_hard_start -
>> >>                                buf->page_offset;
>> >> +
>> >> +                    ctx.priv = priv;
>> >> +                    ctx.p = p;
>> >> +                    ctx.np = np;
>> >> +
>> >>                      skb = stmmac_xdp_run_prog(priv, &ctx.xdp);
>> >>                      /* Due xdp_adjust_tail: DMA sync for_device
>> >>                       * cover max len CPU touch @@ -7071,6 +7076,23
>> >> @@ void stmmac_fpe_handshake(struct stmmac_priv *priv, bool enable)
>> >>      }
>> >>  }
>> >>
>> >> +static int stmmac_xdp_rx_timestamp(const struct xdp_md *_ctx, u64
>> >> +*timestamp) {
>> >> +    const struct stmmac_xdp_buff *ctx = (void *)_ctx;
>> >> +
>> >> +    *timestamp = 0;
>> >> +    stmmac_get_rx_hwtstamp(ctx->priv, ctx->p, ctx->np, timestamp);
>> >> +
>> >
>> > [..]
>> >
>> >> +    if (*timestamp)
>> >
>> > Nit: does it make sense to change stmmac_get_rx_hwtstamp to return
>> > bool to indicate success/failure? Then you can do:
>> >
>> > if (!stmmac_get_rx_hwtstamp())
>> >       reutrn -ENODATA;
>>
>> I would make it return the -ENODATA directly since typically bool
>> true/false functions have names like "stmmac_has_rx_hwtstamp" or
>> similar name that infers you're answering a true/false question.
>>
>> That might also let you avoid zeroing the timestamp value first?
>
>SGTM!

stmmac_get_rx_hwtstamp() is used in other places where return
value is not needed. Additional if statement checking on return value
will add cost, but ignoring return value will hit "unused result" warning.

I think it will be more make sense if I directly retrieve the timestamp value
in stmmac_xdp_rx_timestamp(), instead of reuse stmmac_get_rx_hwtstamp().

Let me send out v4 for review.

Thanks & Regards
Siang

>
>> Thanks,
>> Jake