[Intel-wired-lan] [PATCH intel-next] ice: Don't put stale timestamps in the skb

[Jesse Brandeburg <jesse.brandeburg@intel.com>]

On 11/12/2021 5:53 AM, Karol Kolacinski wrote:
> The driver has to check if it does not accidentally put the timestamp in
> the SKB before previous timestamp gets overwritten.
> Timestamp values in the PHY are read only and do not get cleared except
> at hardware reset or when a new timestamp value is captured.
> The cached_tstamp field is used to detect the case where a new timestamp
> has not yet been captured, ensuring that we avoid sending stale
> timestamp data to the stack.

Missing sign off, please run checkpatch --strict and build tests on your 
patches before sending to the list.

> ---
>   drivers/net/ethernet/intel/ice/ice_ptp.c | 11 ++++-------
>   drivers/net/ethernet/intel/ice/ice_ptp.h |  6 ++++++
>   2 files changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.c b/drivers/net/ethernet/intel/ice/ice_ptp.c
> index 2b3b2060b504..9a1a09661c78 100644
> --- a/drivers/net/ethernet/intel/ice/ice_ptp.c
> +++ b/drivers/net/ethernet/intel/ice/ice_ptp.c
> @@ -2069,19 +2069,16 @@ static void ice_ptp_tx_tstamp_work(struct kthread_work *work)
>   		if (err)
>   			continue;
>   
> -		/* Check if the timestamp is valid */
> -		if (!(raw_tstamp & ICE_PTP_TS_VALID))
> +		/* Check if the timestamp is invalid or stale */
> +		if (!(raw_tstamp & ICE_PTP_TS_VALID) ||
> +		    raw_tstamp == tx->tstamps[idx].cached_tstamp)
>   			continue;
>   
> -		/* clear the timestamp register, so that it won't show valid
> -		 * again when re-used.
> -		 */
> -		ice_clear_phy_tstamp(hw, tx->quad, phy_idx);
> -
>   		/* The timestamp is valid, so we'll go ahead and clear this
>   		 * index and then send the timestamp up to the stack.
>   		 */
>   		spin_lock(&tx->lock);
> +		tx->tstamps[idx].cached_tstamp = raw_tstamp;
>   		clear_bit(idx, tx->in_use);
>   		skb = tx->tstamps[idx].skb;
>   		tx->tstamps[idx].skb = NULL;
> diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.h b/drivers/net/ethernet/intel/ice/ice_ptp.h
> index 92b202ef3c15..eef8ec894871 100644
> --- a/drivers/net/ethernet/intel/ice/ice_ptp.h
> +++ b/drivers/net/ethernet/intel/ice/ice_ptp.h
> @@ -55,15 +55,21 @@ struct ice_perout_channel {
>    * struct ice_tx_tstamp - Tracking for a single Tx timestamp
>    * @skb: pointer to the SKB for this timestamp request
>    * @start: jiffies when the timestamp was first requested
> + * @cached_tstamp: last read timestamp
>    *
>    * This structure tracks a single timestamp request. The SKB pointer is
>    * provided when initiating a request. The start time is used to ensure that
>    * we discard old requests that were not fulfilled within a 2 second time
>    * window.
> + * Timestamp values in the PHY are read only and do not get cleared except at
> + * hardware reset or when a new timestamp value is captured. The cached_tstamp
> + * field is used to detect the case where a new timestamp has not yet been
> + * captured, ensuring that we avoid sending stale timestamp data to the stack.
>    */
>   struct ice_tx_tstamp {
>   	struct sk_buff *skb;
>   	unsigned long start;
> +	u64 cached_tstamp;
>   };
>   
>   /**
>