netdev - Re: [PATCH ethtool] Add the command to show the time stamping capabilities.

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Message-ID: <20120403053717.GA2155@netboy.at.omicron.at>
Date:	Tue, 3 Apr 2012 07:37:17 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	Martin Porter <mporter@...arflare.com>,
	Jacob Keller <jacob.e.keller@...el.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	John Ronciak <john.ronciak@...el.com>,
	e1000-devel@...ts.sourceforge.net
Subject: Re: [PATCH ethtool] Add the command to show the time stamping
 capabilities.

On Mon, Apr 02, 2012 at 08:25:58PM +0100, Ben Hutchings wrote:
> On Sun, 2012-04-01 at 17:23 +0200, Richard Cochran wrote:

> > +	if (info->tx_types & (1 << HWTSTAMP_TX_OFF))
> > +		fprintf(stdout, "HWTSTAMP_TX_OFF\n");
> > +
> > +	if (info->tx_types & (1 << HWTSTAMP_TX_ON))
> > +		fprintf(stdout, "HWTSTAMP_TX_ON\n");
> > +
> > +	if (info->tx_types & (1 << HWTSTAMP_TX_ONESTEP_SYNC))
> > +		fprintf(stdout, "HWTSTAMP_TX_ONESTEP_SYNC\n");
> 
> If there is no hardware timestamping available then shouldn't we see
> HWTSTAMP_TX_OFF reported here?  But that's going to be the case.  Not
> sure whether the kernel or the ethtool utility should deal with that,
> but don't assume the ethtool utility is the only consumer.

Actually, if the device does not support hardware time stamping at
all, then ioctl SIOCSHWTSTAMP returns EOPNOTSUPP. So, HWTSTAMP_TX_ON
means you can turn Tx time stamping on, and HWTSTAMP_TX_OFF means you
can turn it off again. It might not seem too logical, but that is how
the interface works.

So (tx_types == 0) means no hardware timestamping available. We can
print that as a special case, if you think it best.

> Hardware Receive Filter Modes:
> 	none (HWTSTAMP_FILTER_NONE)
> 	ptpv2-l4-event (HWTSTAMP_FILTER_PTP_V2_L4_EVENT)
> 	ptpv2-l4-sync (HWTSTAMP_FILTER_PTP_V2_L4_SYNC)
> 
> (Maybe you can think of better names.)

Okay, I get the idea.

Thanks,
Richard
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