netdev - Re: [PATCH net-next v1 4/4] net: lan966x: generate software timestamp just before the doorbell

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Message-ID: <20250508124047.xyhrabkxsbhceujv@skbuf>
Date: Thu, 8 May 2025 15:40:47 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: Horatiu Vultur <horatiu.vultur@...rochip.com>, irusskikh@...vell.com,
	andrew+netdev@...n.ch, bharat@...lsio.com, ayush.sawal@...lsio.com,
	UNGLinuxDriver@...rochip.com, mcoquelin.stm32@...il.com,
	alexandre.torgue@...s.st.com, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	horms@...nel.org, sgoutham@...vell.com, willemb@...gle.com,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v1 4/4] net: lan966x: generate software
 timestamp just before the doorbell

On Thu, May 08, 2025 at 08:22:39PM +0800, Jason Xing wrote:
> Thanks for the kind reply.
> 
> It looks like how to detect depends on how the bpf prog is written?
> Mostly depends on how the writer handles this data part. Even though
> we don't guarantee on how to ask users/admins to write/adjust their
> bpf codes, it's not that convenient for them if this patch is applied,
> to be frank. I'm not pushing you to accept this patch, just curious on
> "how and why". Now I can guess why you're opposed to it....

The BPF program is not user-generated, it is run in the context of the
function you're moving.

skb_tx_timestamp()
-> skb_clone_tx_timestamp()
   -> classify()
      -> ptp_classify_raw()
         -> bpf_prog_run(ptp_insns, skb)