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

[Jacob Keller <jacob.e.keller@intel.com>]

On 4/12/2023 6:39 PM, Song, Yoong Siang wrote:
> 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.
> 

Isn't unused return values only checked if the function is annotated as
"__must_check"?

> 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().
> 

That makes sense too, the XDP flow is a bit special cased relative to
the other ones.

> Let me send out v4 for review.
> 
> Thanks & Regards
> Siang
> 
>>
>>> Thanks,
>>> Jake