netdev - Re: [PATCH 04/12] phylib: add a way to make PHY time stamps possible.

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Date:	Tue, 15 Jun 2010 10:33:51 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	netdev@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org,
	Krzysztof Halasa <khc@...waw.pl>
Subject: Re: [PATCH 04/12] phylib: add a way to make PHY time stamps possible.

On Tue, Jun 15, 2010 at 10:08 AM, Richard Cochran
<richardcochran@...il.com> wrote:
> This patch adds a new networking option to allow hardware time stamps
> from PHY devices. Using PHY time stamps will still require adding two
> inline function calls to each MAC driver. The CONFIG option makes these
> calls safe to add, since the calls become NOOPs when the option is
> disabled.
>
> Signed-off-by: Richard Cochran <richard.cochran@...cron.at>
> ---
>  include/linux/phy.h    |    4 ++++
>  include/linux/skbuff.h |   32 ++++++++++++++++++++++++++++++++
>  net/Kconfig            |   11 +++++++++++
>  3 files changed, 47 insertions(+), 0 deletions(-)
>
[...]
> diff --git a/net/Kconfig b/net/Kconfig
> index 0d68b40..3fa7ae3 100644
> --- a/net/Kconfig
> +++ b/net/Kconfig
> @@ -86,6 +86,17 @@ config NETWORK_SECMARK
>          to nfmark, but designated for security purposes.
>          If you are unsure how to answer this question, answer N.
>
> +config NETWORK_PHY_TIMESTAMPING
> +       bool "Timestamping in PHY devices"
> +       depends on EXPERIMENTAL
> +       help
> +         This allows timestamping of network packets by PHYs with
> +         hardware timestamping capabilities. This option adds some
> +         overhead in the transmit and receive paths. Note that this
> +         option also requires support in the MAC driver.

Some overhead?  At a brief glance of the series it looks like it could
add a lot of overhead, but I'm not fully clear on what the full
process is.  Can you describe how the hardware timestamping works?  I
could use an overview of what the kernel has to do.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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