netdev - Re: [PATCH iwl-net 3/3] ice: restore timestamp configuration after device reset

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Date: Sat, 4 Nov 2023 11:25:23 -0400
From: Simon Horman <horms@...nel.org>
To: Jacob Keller <jacob.e.keller@...el.com>
Cc: Anthony Nguyen <anthony.l.nguyen@...el.com>,
	Intel Wired LAN <intel-wired-lan@...ts.osuosl.org>,
	netdev@...r.kernel.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [PATCH iwl-net 3/3] ice: restore timestamp configuration after
 device reset

On Fri, Nov 03, 2023 at 04:46:58PM -0700, Jacob Keller wrote:
> The driver calls ice_ptp_cfg_timestamp() during ice_ptp_prepare_for_reset()
> to disable timestamping while the device is resetting. This operation
> destroys the user requested configuration. While the driver does call
> ice_ptp_cfg_timestamp in ice_rebuild() to restore some hardware settings
> after a reset, it unconditionally passes true or false, resulting in
> failure to restore previous user space configuration.
> 
> This results in a device reset forcibly disabling timestamp configuration
> regardless of current user settings.
> 
> This was not detected previously due to a quirk of the LinuxPTP ptp4l
> application. If ptp4l detects a missing timestamp, it enters a fault state
> and performs recovery logic which includes executing SIOCSHWTSTAMP again,
> restoring the now accidentally cleared configuration.
> 
> Not every application does this, and for these applications, timestamps
> will mysteriously stop after a PF reset, without being restored until an
> application restart.
> 
> Fix this by replacing ice_ptp_cfg_timestamp() with two new functions:
> 
> 1) ice_ptp_disable_timestamp_mode() which unconditionally disables the
>    timestamping logic in ice_ptp_prepare_for_reset() and ice_ptp_release()
> 
> 2) ice_ptp_restore_timestamp_mode() which calls
>    ice_ptp_restore_tx_interrupt() to restore Tx timestamping configuration,
>    calls ice_set_rx_tstamp() to restore Rx timestamping configuration, and
>    issues an immediate TSYN_TX interrupt to ensure that timestamps which
>    may have occurred during the device reset get processed.
> 
> Modify the ice_ptp_set_timestamp_mode to directly save the user
> configuration and then call ice_ptp_restore_timestamp_mode. This way, reset
> no longer destroys the saved user configuration.
> 
> This obsoletes the ice_set_tx_tstamp() function which can now be safely
> removed.
> 
> With this change, all devices should now restore Tx and Rx timestamping
> functionality correctly after a PF reset without application intervention.
> 
> Fixes: 77a781155a65 ("ice: enable receive hardware timestamping")
> Fixes: ea9b847cda64 ("ice: enable transmit timestamps for E810 devices")
> Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>

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