netdev - Re: [Intel-wired-lan] [PATCH iwl-next v1 1/1] e1000e: introduce private flag to override XTAL clock frequency

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Message-ID: <91b21af5-6faa-407e-a49f-658bdf186086@intel.com>
Date: Mon, 1 Dec 2025 14:08:59 +0200
From: "Lifshits, Vitaly" <vitaly.lifshits@...el.com>
To: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>,
	"intel-wired-lan@...osl.org" <intel-wired-lan@...osl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "andrew+netdev@...n.ch"
	<andrew+netdev@...n.ch>, "horms@...nel.org" <horms@...nel.org>,
	"kuba@...nel.org" <kuba@...nel.org>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "davem@...emloft.net" <davem@...emloft.net>,
	"pabeni@...hat.com" <pabeni@...hat.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v1 1/1] e1000e: introduce
 private flag to override XTAL clock frequency



On 11/27/2025 9:01 AM, Loktionov, Aleksandr wrote:
> 
> 
>> -----Original Message-----
>> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of
>> Vitaly Lifshits
>> Sent: Thursday, November 27, 2025 5:31 AM
>> To: intel-wired-lan@...osl.org; netdev@...r.kernel.org;
>> andrew+netdev@...n.ch; horms@...nel.org; kuba@...nel.org;
>> edumazet@...gle.com; davem@...emloft.net; pabeni@...hat.com
>> Cc: Lifshits, Vitaly <vitaly.lifshits@...el.com>
>> Subject: [Intel-wired-lan] [PATCH iwl-next v1 1/1] e1000e: introduce private
>> flag to override XTAL clock frequency
>>
>> On some TGP and ADP systems, the hardware XTAL clock is incorrectly set to
> Please expand platform abbreviations ("TGP (Tiger Lake PCH)", "ADP (Alder Lake PCH)") and add minimal test context (kernel ver., device PCI ID, FW, phc_ctl version, and whether CLOCK_REALTIME vs PHC was compared).
> 

Thanks, I'll address this in v2.

>> 24MHz instead of the expected 38.4MHz, causing PTP timer inaccuracies. Since
>> affected systems cannot be reliably detected, introduce an ethtool private
>> flag that allows user-space to override the XTAL clock frequency.
>>
>> Tested on an affected system using the phc_ctl tool:
>>
>> Without the flag:
>>    sudo phc_ctl enp0s31f6 set 0.0 wait 10 get
>>    phc_ctl[...] clock time is 16.000541250 (expected ~10s)
>>
>> With the flag:
>>    sudo phc_ctl enp0s31f6 set 0.0 wait 10 get
>>    phc_ctl[...] clock time is 9.984407212 (expected ~10s)
>>
> If the XTAL override is applied via a devlink driverinit param, this reset is expected and should be documented.
> If it remains a runtime privflag, I think you should explain why a reset is required.
> I'd recommend documenting the reset requirement and user impact (link flap, timestamp discontinuity).
> /* Add a short comment near the reset logic in code and
>     Documentation/networking/devlink/e1000e.rst (if converted to devlink param)
> Or Documentation/networking/ethtool-netlink.rst (if kept as privflag) */
> 

Though your comment might become irrelevant if Andrew's detection 
approach works, I'll still clarify the reset behavior. e1000e is a 
legacy driver and does not support devlink, so the override remains a 
runtime privflag. A reset is currently required to reconfigure PTP 
parameters with the new timinca value.


>> Signed-off-by: Vitaly Lifshits <vitaly.lifshits@...el.com>
>> ---
>>   drivers/net/ethernet/intel/e1000e/e1000.h   |  7 ++--
>>   drivers/net/ethernet/intel/e1000e/ethtool.c | 39 ++++++++++-----------
>> drivers/net/ethernet/intel/e1000e/ich8lan.c |  4 +--
>> drivers/net/ethernet/intel/e1000e/netdev.c  | 18 +++++++---
>>   4 files changed, 39 insertions(+), 29 deletions(-)
>>
> 
> ...
> 
>> --
>> 2.34.1
>