Re: [PATCH iwl-net 1/2] ice: ptp: serialize E825 PHY timer start with PTP lock and incval

[Simon Horman <horms@kernel.org>]

On Sat, Sep 26, 2026 at 12:28:23AM +0200, Grzegorz Nitka wrote:
> From: Maciek Machnikowski <maciej.machnikowski@intel.com>
> 
> ice_start_phy_timer_eth56g() programmed the PHY increment value and
> performed the PHY-to-PHC phase synchronization in two separate PTP
> semaphore critical sections, and touched the shared source command
> register (GLTSYN_CMD via ice_ptp_src_cmd()) and read the source incval
> before acquiring the semaphore at all.
> 
> Because GLTSYN_CMD is a single global register latched for the source
> timer and all PHY ports by GLTSYN_CMD_SYNC, a concurrent adjtime (small
> offset, <= S32_MAX) or adjfine could clobber the source command between
> the incval-init and the phase-sync steps. In the worst case the source
> timer command written by ice_ptp_adj_clock() (ICE_PTP_ADJ_TIME) was
> overwritten by the unlocked ICE_PTP_NOP from ice_start_phy_timer_eth56g(),
> so the adjustment was applied to the PHY ports but not to the PHC. This
> left the E825 PHY clock permanently offset from the PHC, showing up as an
> intermittent clock drift.
> 
> Hold the PTP semaphore across the entire start sequence: acquire it
> before the first shared-register access (ice_ptp_src_cmd()), keep it held
> through the incval read, PHY incval init, and the phase synchronization,
> then release it once. Since the hardware semaphore is not recursive, split
> the phase-sync helper into ice_sync_phy_timer_eth56g_unlocked(), which
> assumes the caller already holds the lock, and call it directly from
> ice_start_phy_timer_eth56g(). The locking wrapper is removed as it no
> longer has any callers.
> 
> Fixes: 781ff8f2d575 ("ice: ptp: serialize E825 PHY timer start with PTP lock")
> Signed-off-by: Maciek Machnikowski <maciej.machnikowski@intel.com>
> Co-developed-by: Grzegorz Nitka <grzegorz.nitka@intel.com>
> Signed-off-by: Grzegorz Nitka <grzegorz.nitka@intel.com>
> Suggested-by: Marc Neustadter <marc.neustadter@intel.com>
> Reviewed-by: Sergey Temerkhanov <sergey.temerkhanov@intel.com>
> Reviewed-by: Milena Olech <milena.olech@intel.com>

Reviewed-by: Simon Horman <horms@kernel.org>

> ---
>  drivers/net/ethernet/intel/ice/ice_ptp_hw.c | 48 +++++++++------------
>  1 file changed, 21 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_ptp_hw.c b/drivers/net/ethernet/intel/ice/ice_ptp_hw.c
> index 20bd1813650f..d3e4aeb7e496 100644
> --- a/drivers/net/ethernet/intel/ice/ice_ptp_hw.c
> +++ b/drivers/net/ethernet/intel/ice/ice_ptp_hw.c
> @@ -2045,7 +2045,7 @@ static int ice_read_phy_and_phc_time_eth56g(struct ice_hw *hw, u8 port,
>  }
>  
>  /**
> - * ice_sync_phy_timer_eth56g - Synchronize the PHY timer with PHC timer
> + * ice_sync_phy_timer_eth56g_unlocked - Synchronize the PHY timer with PHC timer

nit: I'm not entirely sure renaming the function is warranted.
     But it's your call.

>   * @hw: pointer to the HW struct
>   * @port: the PHY port to synchronize
>   *

...