On Sat, Nov 08, 2025 at 04:06:13PM +0800, Song Yoong Siang wrote:
> Change eth_igc_read_clock() to read from hardware timestamp registers
> (E1000_SYSTIML/E1000_SYSTIMH) instead of using system clock_gettime().
>
> This ensures that the clock reading is consistent with the hardware's
> internal time base used for Qbv cycle and launch time scheduling,
> providing better accuracy for Time-Sensitive Networking applications.
>
> Fixes: 9630f7c71ecd ("net/igc: enable launch time offloading")
> Cc: [email protected]
>
> Signed-off-by: David Zage <[email protected]>
> Signed-off-by: Song Yoong Siang <[email protected]>
> ---
> v1:
> https://patches.dpdk.org/project/dpdk/patch/[email protected]/
>
> changelog:
> v1 -> v2
> - reuse the existing eth_igc_timesync_read_time() (Soumyadeep).
> ---
> drivers/net/intel/e1000/igc_ethdev.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/intel/e1000/igc_ethdev.c
> b/drivers/net/intel/e1000/igc_ethdev.c
> index b9c91d2446..d4edc82668 100644
> --- a/drivers/net/intel/e1000/igc_ethdev.c
> +++ b/drivers/net/intel/e1000/igc_ethdev.c
> @@ -2813,6 +2813,12 @@ eth_igc_timesync_read_time(struct rte_eth_dev *dev,
> struct timespec *ts)
> {
> struct e1000_hw *hw = IGC_DEV_PRIVATE_HW(dev);
>
> + /*
> + * Reading the SYSTIML register latches the upper 32 bits to the SYSTIMH
> + * shadow register for coherent access. As long as we read SYSTIML first
> + * followed by SYSTIMH, we avoid race conditions where the time rolls
> + * over between the two register reads.
> + */
Not sure this is true. If the nsec value == 999,999,999 on read, then the
rollover occurs, the resulting timestamp will be almost 1 second out,
right?
Instead, you should probably do one of:
* read nsec, then sec, then nsec again and verify that nsec2 > nsec1
* read sec, nsec, then sec, and verify that sec2 == sec1
in both casees retrying the reads if the condition fails.
> ts->tv_nsec = E1000_READ_REG(hw, E1000_SYSTIML);
> ts->tv_sec = E1000_READ_REG(hw, E1000_SYSTIMH);
>
> @@ -2972,10 +2978,10 @@ eth_igc_timesync_disable(struct rte_eth_dev *dev)
> static int
> eth_igc_read_clock(__rte_unused struct rte_eth_dev *dev, uint64_t *clock)
> {
> - struct timespec system_time;
> + struct timespec ts;
>
> - clock_gettime(CLOCK_REALTIME, &system_time);
> - *clock = system_time.tv_sec * NSEC_PER_SEC + system_time.tv_nsec;
> + eth_igc_timesync_read_time(dev, &ts);
> + *clock = rte_timespec_to_ns(&ts);
>
> return 0;
> }
> --
> 2.48.1
>
