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Date:	Sun, 23 Nov 2014 19:04:57 +0000
From:	Ben Hutchings <>
To:	David Miller <>
Subject: Re: [PATCH net-next] vlan: Pass ethtool get_ts_info queries to real

On Sun, 2014-11-23 at 13:48 -0500, David Miller wrote:
> From: Richard Cochran <>
> Date: Sun, 23 Nov 2014 17:05:35 +0100
> > On Sun, Nov 23, 2014 at 03:15:12AM +0000, Ben Hutchings wrote:
> >> 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.
> > 
> > Unsafe? How?
> > 
> > Do you mean that some HW cannot identify and time stamp PTP frames
> > when VLAN tagged? That is surely disappointing for people who shell
> > out money for such cards, but it is hardly unsafe.
> Ben, you will have to provide a concrete example of a chip that will
> do the wrong thing with Richard's change.
> Hypotheticals won't cut it.

The two datasheets I've looked at so far (EG20T for pch_gbe driver,
BF518 for bfin_mac driver) mention support for 802.1q but not 802.1ad.
I already mentioned ptp_classify.c doesn't support 802.1ad, and I can't
see how it would ever make sense to run PTP directly over 802.1ad

I'll read some more datasheets to see whether 802.1q is generally
supported, but for 802.1ad VLAN devices I think we should pass-through
only the NONE and ALL filter capabilities.


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

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