netdev - Re: [net-next 10/13] igb: Tidy up wrapping for CONFIG_IGB

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Date:	Sat, 25 Aug 2012 08:20:13 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	"Keller, Jacob E" <jacob.e.keller@...el.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	"Vick, Matthew" <matthew.vick@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>
Subject: Re: [net-next 10/13] igb: Tidy up wrapping for CONFIG_IGB_PTP.

On Fri, Aug 24, 2012 at 07:38:38PM +0000, Keller, Jacob E wrote:

> The IGP_PTP is necessary otherwise you have to do something like #if defined(CONFIG_PTP_1588_CLOCK), or #ifdef CONFIG_PTP_1588_CLOCK \ #ifdef CONFIG_PTP_1588_CLOCK_MODULE

Yes, but maybe use IGP_PTP as Ben described? 

> The main reason that I wouldn't want to un-wrap the timestamping is because the hwtstamp ioctl is somewhat problematic because it is almost all ptp only. Also, some of the parts for igb driver don't support timestamp all, they only support ptp only packets, and this would be a lot more confusing since I would say still only allow that if ptp is on.. (since those values are useless except with the PHC clock)

I keep trying to explain that receive time stamping (HWTSTAMP_FILTER_ALL)
is useful all by itself. It has nothing to do with PTP, and the 82580
can do this with very little ** overhead.

I myself have used this feature when debugging and profiling quasi
real time Ethernet protocols like EtherCAT and IEC61850-9-2. The other
drivers that offer this (gianfar and vxge) do so without any CONFIG
conditionals.

IMHO, the Rx time stamping feature should always be available. It is
really not much different than the vlan feature.

Thanks,
Richard

** Both igb_rx_hwtstamp and igb_tx_hwtstamp only add a single test
   when time stamping is not enabled.

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