On 2/5/2026 4:20 AM, Loktionov, Aleksandr wrote:
-----Original Message-----
From: Intel-wired-lan <[email protected]> On Behalf
Of Kurt Kanzenbach
Sent: Thursday, February 5, 2026 12:58 PM
To: Loktionov, Aleksandr <[email protected]>; Nguyen,
Anthony L <[email protected]>; Kitszel, Przemyslaw
<[email protected]>
Cc: Paul Menzel <[email protected]>; Vadim Fedorenko
<[email protected]>; Gomes, Vinicius
<[email protected]>; [email protected]; Richard Cochran
<[email protected]>; [email protected]; Andrew Lunn
<[email protected]>; Eric Dumazet <[email protected]>; intel-
[email protected]; Keller, Jacob E
<[email protected]>; Jakub Kicinski <[email protected]>; Paolo
Abeni <[email protected]>; David S. Miller <[email protected]>;
Sebastian Andrzej Siewior <[email protected]>
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
Thank you, Kurt for sharing your experience. I don't have so many experience
with RT Linux.
For me calling a function, not designed to be called from IRQ context is a SUS.
So, I rose the question about sleeping.
My understanding is that RT is only safe to convert such spinlock_t to
mutex *because* it also converts IRQs to threads.
