netdev - Re: [Intel-wired-lan] [PATCH iwl-next v7 12/12] iavf: add support for Rx timestamps to hotpath

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Message-ID: <20240608130019.GE27689@kernel.org>
Date: Sat, 8 Jun 2024 14:00:19 +0100
From: Simon Horman <horms@...nel.org>
To: Mateusz Polchlopek <mateusz.polchlopek@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	Jacob Keller <jacob.e.keller@...el.com>,
	Wojciech Drewek <wojciech.drewek@...el.com>,
	Rahul Rameshbabu <rrameshbabu@...dia.com>,
	Sunil Goutham <sgoutham@...vell.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v7 12/12] iavf: add support
 for Rx timestamps to hotpath

On Tue, Jun 04, 2024 at 09:14:00AM -0400, Mateusz Polchlopek wrote:
> From: Jacob Keller <jacob.e.keller@...el.com>
> 
> Add support for receive timestamps to the Rx hotpath. This support only
> works when using the flexible descriptor format, so make sure that we
> request this format by default if we have receive timestamp support
> available in the PTP capabilities.
> 
> In order to report the timestamps to userspace, we need to perform
> timestamp extension. The Rx descriptor does actually contain the "40
> bit" timestamp. However, upper 32 bits which contain nanoseconds are
> conveniently stored separately in the descriptor. We could extract the
> 32bits and lower 8 bits, then perform a bitwise OR to calculate the
> 40bit value. This makes no sense, because the timestamp extension
> algorithm would simply discard the lower 8 bits anyways.
> 
> Thus, implement timestamp extension as iavf_ptp_extend_32b_timestamp(),
> and extract and forward only the 32bits of nominal nanoseconds.
> 
> Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
> Reviewed-by: Wojciech Drewek <wojciech.drewek@...el.com>
> Reviewed-by: Rahul Rameshbabu <rrameshbabu@...dia.com>
> Reviewed-by: Sunil Goutham <sgoutham@...vell.com>
> Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@...el.com>

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