Re: [PATCH] e1000e: set fixed clock frequency indication for Alder Point

[Simon Horman <horms@kernel.org>]

On Thu, Sep 03, 2026 at 06:06:33PM +0000, Rawda, Tony wrote:
> On some Alder Point (e1000_pch_adp) platforms the XTAL value reported in
> the software STRAP is incorrect, so the SYSCFI bit in TSYNCRXCTL selects
> a 24 MHz base frequency while the SYSTIM counter actually advances at
> 38.4 MHz. As a result the PTP hardware clock runs ~1.6x too fast
> (38.4/24), which prevents ptp4l and other PTP-based time sync from
> disciplining the clock.
> 
> Commit 688a0d61b2d7 ("e1000e: set fixed clock frequency indication for
> Nahum 11 and Nahum 13") fixed the same problem for e1000_pch_mtp,
> e1000_pch_lnp and e1000_pch_ptp. Alder Point silicon likewise always
> runs at 38.4 MHz, so give it the same fixed-frequency override in both
> e1000e_get_base_timinca() and e1000e_ptp_init().
> 
> Observed on an HP Z2 Mini G9 with I219-LM (17) [8086:1a1c]: before the
> change the PHC advanced 16.0 s per 10.0 s of wall-clock time and
> /sys/class/ptp/ptpN/max_adjustment read 999999999 (MAX_PPB_24MHZ);
> afterwards it advances ~10.0 s and max_adjustment reads 230769100
> (MAX_PPB_38400KHZ).
> 
> Fixes: 59e466888038 ("e1000e: Add support for Alder Lake")
> Cc: stable@vger.kernel.org
> Signed-off-by: Tony Rawda <Tony.Rawda@disney.com>

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