Re: [PATCH] net: ethernet: ti: cpsw: allow to configure min tx packet size

[Lad, Prabhakar]

Hi Andrew,

On Mon, Nov 26, 2018 at 2:27 AM Andrew Lunn <andrew@xxxxxxx> wrote:
>
> On Sun, Nov 25, 2018 at 05:43:15PM -0600, Grygorii Strashko wrote:
> > For proper VLAN packets forwarding CPSW driver uses min tx packet size of
> > 64bytes (VLAN_ETH_ZLEN, excluding ETH_FCS) which was corrected by
> > commit 9421c9015047 ("net: ethernet: ti: cpsw: fix min eth packet size").
> >
> > Unfortunately, this breaks some industrial automation protocols, as
> > reported by TI customers [1], which can work only with min TX packet size
> > from 60 byte (ecluding FCS).
>
> Hi Grygorii
>
> excluding...
>
> > Hence, introduce module boot parameter "tx_packet_min" to allow configure
> > min TX packet size at boot time.
>
> Module parameters are generally not liked.
>
> What actually happens here with this lower limit? Does the hardware
> send runt packets? Does the protocol actually require runt packets?
>
Yes it does send runt packets,  and also get Rx align errors. you can
find the ethtool dump at [1].

[1] https://e2e.ti.com/support/processors/f/791/t/719557?Linux-AM5728-EtherCAT-packets-dropped

Cheers,
--Prabhakar Lad