Re: [Linuxptp-devel] Clarification of PHC and PHY on the supported lists?

[George Neville-N. <gn...@ne...>]

On Dec 2, 2013, at 16:46 , Richard Cochran <ric...@gm...> wrote:

> On Mon, Dec 02, 2013 at 03:37:28PM -0500, George Neville-Neil wrote:
>> Hi,
>> 
>> I am trying to determine why the hardware timestamping support table only lists PHC and not PHY
>> timestamping. Testing on a system with an Intel 82576 NIC, I was unable, even with a very recent kernel (3.10)
>> to get PHY level time stamping.  
> 
> Hi George,
> 
> As you know, there are both MACs and PHYs on the market with hardware
> time stamping and clock functionality. Linux supports both, but not at
> the same time on the same port. Right now, the dp83640 is only PHY
> driver in the kernel with time stamping and PHC supported.
> 
> [ Looking at the table, I see that it really doesn't tell you whether
>  the part in question is a MAC or PHY. This can be improved. ]
> 
> In order to allow PHY time stamping and PHC functions, the MAC driver
> has to play along too, and not all MAC drivers can do this. So the
> "PHY" column is really saying whether you can combine that MAC with a
> PTP capable PHY or not. The PTP MACs all have "NA" (Not Applicable)
> because you cannot have time stamping in both the MAC and the PHY.
> 
> Your card, the 82576, does support MAC time stamping and PHC
> functions, at it should work in 3.10 kernel. But even if you combine
> it with a PTP capable PHY (like the dp83640), the PHY time stamping
> won't work.
> 
>> Do I need to build a custom kernel for this to work?
> 
> To support time stamping in the PHY, your kernel needs to have option
> CONFIG_NETWORK_PHY_TIMESTAMPING enabled. Since this adds extra checks
> into the hot path, probably no distro kernel will turn it on. So, yes,
> you will have to recompile if you want PHY time stamping. (And you
> will also need the dp83640 combined with a MAC in the table for which
> PHY=Y.)
> 

Thanks for the detailed reply.  I think I get it now.    BTW You might just cut/paste your
response to me into the Wiki.

Best,
George