Re: [PATCH net-next 0/2] net: stmmac: correctly populate ptp_clock_ops.getcrosststamp

[Simon Horman <horms@kernel.org>]

On Wed, Sep 03, 2025 at 03:00:16PM +0100, Russell King (Oracle) wrote:
> Hi,
> 
> While reviewing code in the stmmac PTP driver, I noticed that the
> getcrosststamp() method is always populated, irrespective of whether
> it is implemented or not by the stmmac platform specific glue layer.
> 
> Where a platform specific glue layer does not implement it, the core
> stmmac driver code returns -EOPNOTSUPP. However, the PTP clock core
> code uses the presence of the method in ptp_clock_ops to determine
> whether this facility should be advertised to userspace (see
> ptp_clock_getcaps()).
> 
> Moreover, the only platform glue that implements this method is the
> Intel glue, and for it not to return -EOPNOTSUPP, the CPU has to
> support X86_FEATURE_ART.
> 
> This series updates the core stmmac code to only provide the
> getcrosststamp() method in ptp_clock_ops when the platform glue code
> provides an implementation, and then updates the Intel glue code to
> only provide its implementation when the CPU has the necessary
> X86_FEATURE_ART feature.
> 
> As I do not have an Intel card to test with, these changes are
> untested, so if anyone has such a card, please test. Thanks.

Hi Russell,

Although not strictly related to stmmac,
I am wondering if similar treatment is appropriate for:

* drivers/virtio/virtio_rtc_ptp.c:viortc_ptp_getcrosststamp
* drivers/net/ethernet/intel/ice/ice_ptp.c:ice_ptp_getcrosststamp

And if some sort of documentation of the behaviour you describe is
appropriate. Say in the Kernel doc for struct ptp_clock_info.