linux-kernel - RE: [Intel-wired-lan] [PATCH iwl-next v3] igb: Retrieve Tx timestamp directly from interrupt for i210

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Message-ID: <87ikcbwgf3.fsf@jax.kurt.home>
Date: Thu, 05 Feb 2026 12:58:24 +0100
From: Kurt Kanzenbach <kurt@...utronix.de>
To: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>, "Nguyen, Anthony
 L" <anthony.l.nguyen@...el.com>, "Kitszel, Przemyslaw"
 <przemyslaw.kitszel@...el.com>
Cc: Paul Menzel <pmenzel@...gen.mpg.de>, Vadim Fedorenko
 <vadim.fedorenko@...ux.dev>, "Gomes, Vinicius" <vinicius.gomes@...el.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Richard Cochran
 <richardcochran@...il.com>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, Andrew Lunn <andrew+netdev@...n.ch>, Eric
 Dumazet <edumazet@...gle.com>, "intel-wired-lan@...ts.osuosl.org"
 <intel-wired-lan@...ts.osuosl.org>, "Keller, Jacob E"
 <jacob.e.keller@...el.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, "David S. Miller" <davem@...emloft.net>, Sebastian
 Andrzej Siewior <bigeasy@...utronix.de>
Subject: RE: [Intel-wired-lan] [PATCH iwl-next v3] igb: Retrieve Tx
 timestamp directly from interrupt for i210

On Thu Feb 05 2026, Loktionov, Aleksandr wrote:
>> +/**
>> + * igb_ptp_tx_tstamp_event
>> + * @adapter: pointer to igb adapter
>> + *
>> + * This function checks the TSYNCTXCTL valid bit and stores the Tx
>> +hardware
>> + * timestamp at the current skb.
>> + **/
>> +void igb_ptp_tx_tstamp_event(struct igb_adapter *adapter) {
>> +	struct e1000_hw *hw = &adapter->hw;
>> +	u32 tsynctxctl;
>> +
>> +	if (!adapter->ptp_tx_skb)
>> +		return;
>> +
>> +	tsynctxctl = rd32(E1000_TSYNCTXCTL);
>> +	if (WARN_ON_ONCE(!(tsynctxctl & E1000_TSYNCTXCTL_VALID)))
>> +		return;
>> +
>> +	igb_ptp_tx_hwtstamp(adapter); <-Calls existing function designed for work queue!
>
> skb_tstamp_tx() can sleep
> Smells like sleep-in-atomic isn't it?

AFAICS skb_tstamp_tx() is safe to call here.

> spin_lock_irqsave(&wq_head->lock, flags);  <- RT mutex can sleep

In case you're worried about PREEMPT_RT: On -RT the IRQ runs a dedicated
thread. BTW I've tested this with and without -RT and with
CONFIG_DEBUG_ATOMIC_SLEEP.

Thanks,
Kurt

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