Re: [PATCH] net/iavf: negotiate PTP with PF before reporting Rx timestamping

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Dec 10, 2025 at 01:45:52PM -0800, Jacob Keller wrote:
> The iavf driver has support for hardware Rx timestamps since commit h
> b5cd735132f6 ("net/iavf: enable Rx timestamp on flex descriptor").
> 
> To enable this, the VF must first negotiate PTP capabilities with the PF
> by sending the VIRTCHNL_OP_1588_PTP_GET_CAPS command, with the requested
> capabilities. The PF will respond with the actually supported subset of
> capabilities.
> 
> The PF may not actually enable Rx timestamping, even if it reports the
> overall PTP capability support. If this happens, the iavf driver logic
> will incorrectly report that Rx timestamps can be enabled despite being
> rejected by the PF.
> 
> This should be unlikely in practice, as most PFs which support the
> VIRTCHNL_VF_CAP_PTP will support Rx timestamping. However, there are
> some cases where this may not be true. In particular, there is an
> unfortunate issue with some versions of the ice PF using a different
> structure layout that prevents the PF from enabling Rx timestamping.
> 
> To prevent this, the DPDK driver should check the capabilities and
> confirm that the PF did enable Rx timestamping, instead of assuming it
> will be enabled by all PFs that support the VIRTCHNL_CAP_PTP feature.
> This prevents the DPDK application from attempting to enable Rx
> timestamps when the PF will not support it.
> 
> Currently, the DPDK driver only negotiates PTP capabilities when the
> device is started. First, check the capabilities during iavf_dev_init()
> so that the iavf_dev_info_get() function has the required knowledge.
> Then, only set RTE_ETH_RX_OFFLOAD_TIMESTAMP when the PF has informed
> that it enabled support.
> 
> Continue to re-check the PTP capabilities in iavf_dev_start(), as it is
> important to renegotiate after device reset.
> 
> Fixes: d21c2fe6e5a1 ("net/iavf: fix check for PF Rx timestamp support")
> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
> ---
> This is a new version of the fix to prevent enabling Rx timestamps on PFs
> which do not enable it when negotiating capabilities. It combines the
> original fix along with the additional requirement of negotiating the PTP
> capabilities during iavf_dev_init().
> ---
> 
> ---
>  drivers/net/intel/iavf/iavf_ethdev.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

Applied to dpdk-next-net-intel,

Thanks,
/Bruce