Re: [Linuxptp-users] bad message due to padding of FOLLOW_UP and DELAY_REQ

[Peter B. <pe...@be...>]

On 2022-01-13 05:11, Richard Cochran wrote:
> On Wed, Jan 12, 2022 at 03:57:55PM +0100, Peter Bergin wrote:
>
>> I have a setup with TI processor using the cpsw driver from Linux mainline,
>> kernel version 5.4. I'm using IEEE 802.3 network transport and sending PTP
>> frames on Ethernet. When sending SYNC, FOLLOW_UP and DELAY_REQ that has a
>> length of 58 bytes they get padded up to 64 bytes.
> I tried layer2 with a Beagle Board Black (am335x), and I also saw the
> SIX bytes of padding.  Wireshark hates this, and shows a FCS error
> (but actually I think it assumes the last 4 bytes are FCS, but in fact
> the FCS has been stripped by the MAX)
>
> As Miroslav pointed out, padding SIX bytes is wrong.
>
>> On the other side in my setup I have a PC with e1000e driver. On that side
>> when sending SYNC, FOLLOW_UP and DELAY_REQ over Ethernet the PDUs are padded
>> to 60 bytes.
> This is correct.
>
>      44 (PTP PDU) + 14 (L2 dst+src+type) + 4 (FCS) = 62 bytes
>
> Two bytes padding are needed to make 64 bytes.  Not SIX bytes.
>
> The TI MAC (or driver?) is padding six bytes instead of two.
>
> Somebody should tell TI about their bug.
>
Thanks for the confirmation Richard! I did some more research around 
this and it turned out is was already fixed in v5.14 upstream. For 
reference: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=acc68b8d2a1196c4db806947606f162dbeed2274 


Backporting relevant stuff of this patch to my 5.4 kernel solved the 
padding problem.

/Peter