linux-kernel - Re: [PATCH net-next v4 0/8] gve: Add Rx HW timestamping support

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Message-ID: <20250610182348.03069023@kernel.org>
Date: Tue, 10 Jun 2025 18:23:48 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Harshitha Ramamurthy <hramamurthy@...gle.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, jeroendb@...gle.com, andrew+netdev@...n.ch,
 willemb@...gle.com, ziweixiao@...gle.com, pkaligineedi@...gle.com,
 yyd@...gle.com, joshwash@...gle.com, shailend@...gle.com,
 linux@...blig.org, thostet@...gle.com, jfraker@...gle.com,
 richardcochran@...il.com, jdamato@...tly.com, vadim.fedorenko@...ux.dev,
 horms@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4 0/8] gve: Add Rx HW timestamping support

On Mon,  9 Jun 2025 18:40:21 +0000 Harshitha Ramamurthy wrote:
> This patch series add the support of Rx HW timestamping, which sends
> adminq commands periodically to the device for clock synchronization with
> the nic.

IIUC:
 - the driver will only register the PHC if timestamping is enabled
   (and unregister it when disabled),
 - there is no way to read the PHC from user space other than via
   packet timestamps,
 - the ethtool API does not report which PHC is associated with the
   NIC, presumably because the PHC is useless to the user space.

Do I understand that correctly? It's pretty unusual. Why not let user
read the clock?

Why unregister the PHC? I understand that you may want to cancel 
the quite aggressive timestamp refresh work, but why kill the whole
clock... Perhaps ptp_cancel_worker_sync() didn't exist when you wrote
this code?