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Date:   Wed, 12 Apr 2023 13:55:54 -0700
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Subject: Re: [PATCH net-next v3 3/4] net: stmmac: add Rx HWTS metadata to XDP
 receive pkt
Content-Language: en-US
To:     Stanislav Fomichev <sdf@google.com>,
        Song Yoong Siang <yoong.siang.song@intel.com>
CC:     Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        "Jakub Kicinski" <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        "Daniel Borkmann" <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Alexander Duyck <alexanderduyck@fb.com>,
        Ong Boon Leong <boon.leong.ong@intel.com>,
        <netdev@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <bpf@vger.kernel.org>,
        <xdp-hints@xdp-project.net>
References: <20230412094235.589089-1-yoong.siang.song@intel.com>
 <20230412094235.589089-4-yoong.siang.song@intel.com>
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From:   Jacob Keller <jacob.e.keller@intel.com>
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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?

Thanks,
Jake