RE: [PATCH net 2/5] e1000e: do not cache the hwtstamp config before it is applied

[Loktionov, Aleksandr]

> -----Original Message-----
> From: Linkui Xiao <xiaolinkui@xxxxxxx>
> Sent: Wednesday, October 28, 2026 10:05 AM
> To: Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>; Kitszel, Przemyslaw
> <przemyslaw.kitszel@xxxxxxxxx>; andrew+netdev@xxxxxxx;
> davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> pabeni@xxxxxxxxxx
> Cc: intel-wired-lan@xxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Linkui Xiao <xiaolinkui@xxxxxxxxxx>;
> stable@xxxxxxxxxxxxxxx
> Subject: [PATCH net 2/5] e1000e: do not cache the hwtstamp config before
> it is applied
> 
> From: Linkui Xiao <xiaolinkui@xxxxxxxxxx>
> 
> e1000e_config_hwtstamp() stores the requested configuration in
> adapter->hwtstamp_config right after the rx filter has been
> translated, but the two register writes that follow are verified by
> reading the registers back and each of them can fail with -EAGAIN.
> 
> When one of them does, the driver is left holding a configuration the
> hardware never accepted:
> 
>  - e1000e_hwtstamp_get() hands it back to user space, so an
>    application that reads the configuration back is told that
>    hardware time stamping is in effect while it is not;
> 
>  - e1000e_systim_reset() re-applies it after every reset, including
>    the ones the watchdog triggers, and keeps failing;
> 
>  - e1000_watchdog() starts polling TSYNCRXCTL_VALID for the cached rx
>    filter, and e1000_xmit_frame() still parks skbs that ask for a Tx
>    time stamp because it only looks at FLAG_HAS_HW_TIMESTAMP, so they
>    are eventually dropped by e1000e_tx_hwtstamp_work() with a
>    "clearing Tx timestamp hang" warning.
> 
> Cache the configuration only once both registers have been verified, so
> that adapter->hwtstamp_config always describes what the hardware is
> programmed with.
> 
> Fixes: 62d7e3a2d006 ("e1000e: Validate hwtstamp_config completely before
> applying it")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Linkui Xiao <xiaolinkui@xxxxxxxxxx>
> ---
>  drivers/net/ethernet/intel/e1000e/netdev.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c
> b/drivers/net/ethernet/intel/e1000e/netdev.c
> index 35f5590228eb..7ae33273734f 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -3715,8 +3715,6 @@ static int e1000e_config_hwtstamp(struct
> e1000_adapter *adapter,
>  		return -ERANGE;
>  	}
> 
> -	adapter->hwtstamp_config = *config;
> -
>  	/* enable/disable Tx h/w time stamping */
>  	regval = er32(TSYNCTXCTL);
>  	regval &= ~E1000_TSYNCTXCTL_ENABLED;
> @@ -3763,6 +3761,8 @@ static int e1000e_config_hwtstamp(struct
> e1000_adapter *adapter,
>  	er32(RXSTMPH);
>  	er32(TXSTMPH);
> 
> +	adapter->hwtstamp_config = *config;
> +
>  	return 0;
>  }
> 
> --
> 2.25.1

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@xxxxxxxxx>