netdev - Re: [PATCH net-next] vlan: Pass ethtool get_ts

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Date:	Sun, 23 Nov 2014 03:15:12 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	Stefan Sørensen 
	<stefan.sorensen@...ctralink.com>
Subject: Re: [PATCH net-next] vlan: Pass ethtool get_ts_info queries to real
 device.

On Fri, 2014-11-21 at 14:16 +0100, Richard Cochran wrote:
> Commit a6111d3c "vlan: Pass SIOC[SG]HWTSTAMP ioctls to real device"
> intended to enable hardware time stamping on VLAN interfaces, but
> passing SIOCSHWTSTAMP is only half of the story. This patch adds
> the second half, by letting user space find out the time stamping
> capabilities of the device backing a VLAN interface.
[...]

This assumes that the same PTP capabilities apply to VLAN-tagged frames.
I don't think it's at all safe to assume that RX filter modes other than
HWTSTAMP_FILTER_ALL will include VLAN-tagged frames.  I think it is
necessary to define additional modes that explicitly include VLAN-tagged
frames.

I also disagree in general that reconfiguring a VLAN device should make
changes to the underlying device that affect more than just that VLAN,
i.e. SIOCSHWTSTAMP should not be passed through.  SIOCGHWTSTAMP could be
passed through, but rx_filter would need adjustment (VLAN-tagged modes
on the underlying devices become untagged modes on the VLAN device).

Ben.

-- 
Ben Hutchings
Never put off till tomorrow what you can avoid all together.

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