Subject: Re: [RFC][PATCH 1/1] net: support for hardware timestamping

From: Stephen Hemminger <[email-masked]>
Date: Tue, 29 Jul 2008 08:54:57 -0700

On Tue, 29 Jul 2008 16:52:43 +0200
Patrick Ohly <[email-masked]> wrote:

> On Tue, 2008-07-29 at 03:08 +0300, Octavian Purdila wrote:
> > New socket option and socket control message are added as well
> > (SO_TIMESTAMPHW and SCM_TIMESTAMPHW).
> 
> How is a network driver notified that it is expected to do hardware time
> stamping? The connection between the socket option and the driver isn't
> quite clear to me (which might very well be due to my lack of experience
> in this area - please bear with me...). Is the driver expected to check
> the socket flags whenever it gets a chance?
> 
> IMHO it would be necessary to attach this configuration change not just
> to a socket, but also to a message which is then routed to the right
> device driver.
>
In my sky2 sample code, I took a different approach:
 1. Why have HW timestamps different than existing timestamps? If you
    just use existing timestamp, no socket API is needed.
 2. Driver can periodically check if socket timestamping is enabled,
    (atomic_read(&netstamp_needed)) and enable hardware stamping then.
    Alternatively, add a new notifier to net_enable_timestamp() and
    net_disable_timestamp().