Re: [PATCH v3] net/ice: fix incorrect reading of PHY timestamp

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Nov 04, 2024 at 10:31:12AM +0000, Soumyadeep Hore wrote:
> In ICE PMD, previously the ready bitmap checking before reading
> PHY timestamp was not present. This caused incorrect Tx
> timestamping.
> 
> The ready bitmap checking is enabled and PHY timestamp is read once
> the ready bitmap gives positive value.
> 
> Fixes: 881169950d80 ("net/ice/base: implement initial PTP support for E830")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Soumyadeep Hore <soumyadeep.hore@intel.com>
> ---
> v3:
> - Decreased the end time delay from 1 second to 10 microseconds
> ---
> v2:
> - Addressed Bruce's comments
> ---
>  drivers/net/ice/ice_ethdev.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ice/ice_ethdev.c b/drivers/net/ice/ice_ethdev.c
> index 70298ac330..3c768b6d0b 100644
> --- a/drivers/net/ice/ice_ethdev.c
> +++ b/drivers/net/ice/ice_ethdev.c
> @@ -6597,10 +6597,27 @@ ice_timesync_read_tx_timestamp(struct rte_eth_dev *dev,
>  	struct ice_hw *hw = ICE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
>  	struct ice_adapter *ad =
>  			ICE_DEV_PRIVATE_TO_ADAPTER(dev->data->dev_private);
> -	uint64_t ts_ns, tstamp;
> +	uint64_t ts_ns, tstamp, tstamp_ready = 0;
> +	uint64_t end_time;
>  	const uint64_t mask = 0xFFFFFFFF;
>  	int ret;
>  
> +	/* Set the end time with a delay of 10 microseconds */
> +	end_time = rte_get_timer_cycles() + (rte_get_timer_hz() / 100000);
> +
> +	while (!(tstamp_ready & BIT_ULL(0))) {

Nit: in DPDK, we recommend using "== 0" explicitly for numeric comparisons.
The "!" should only be used for boolean values, not ints.

> +		ret = ice_get_phy_tx_tstamp_ready(hw, ad->ptp_tx_block, &tstamp_ready);
> +		if (ret) {
> +			PMD_DRV_LOG(ERR, "Failed to get phy ready for timestamp");
> +			return -1;
> +		}
> +
> +		if (rte_get_timer_cycles() > end_time) {
> +			PMD_DRV_LOG(ERR, "Timeout to get phy ready for timestamp");
> +			return -1;
> +		}

Sorry for the last minute feedback here, but shouldn't these two conditions
be the other way around? Right now, if you call ice_get_phy_tx_tstamp_ready
just as the timer expires, and if the timestamp is actually ready this
time, you will exit with error instead of handling the timestamp.

Also, a very minor issue, but since you always want to go through the loop
at least once, a do { } while(0) might be a better construct. It would
avoid you having to initialize tstamp_ready to zero (not that it matters).

	do {
		if (rte_get_timer_cycles() > end_time) {
			/* log error and return */
		}

		if (ice_get_phy_tx_tstamp_ready(...) != 0) {
			/* error log and return */
		}
	} while((tstamp_ready & BIT_ULL(0)) == 0);

> +	}
> +
>  	ret = ice_read_phy_tstamp(hw, ad->ptp_tx_block, ad->ptp_tx_index, &tstamp);
>  	if (ret || tstamp == 0) {
>  		PMD_DRV_LOG(ERR, "Failed to read phy timestamp");
> -- 

Regards,
/Bruce