RE: [PATCH v2 net-next] net: pcs: Enable pre-emption packet for 10/100Mbps

[Ismail, Mohammad Athari]

Hi Vladimir,

> -----Original Message-----
> From: Vladimir Oltean <olteanv@xxxxxxxxx>
> Sent: Friday, April 23, 2021 7:53 AM
> To: Ismail, Mohammad Athari <mohammad.athari.ismail@xxxxxxxxx>
> Cc: Alexandre Torgue <alexandre.torgue@xxxxxx>; Jose Abreu
> <joabreu@xxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Jakub
> Kicinski <kuba@xxxxxxxxxx>; Andrew Lunn <andrew@xxxxxxx>; Heiner Kallweit
> <hkallweit1@xxxxxxxxx>; Russell King <linux@xxxxxxxxxxxxxxx>; Ong, Boon
> Leong <boon.leong.ong@xxxxxxxxx>; Voon, Weifeng
> <weifeng.voon@xxxxxxxxx>; Wong, Vee Khee <vee.khee.wong@xxxxxxxxx>;
> netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2 net-next] net: pcs: Enable pre-emption packet for
> 10/100Mbps
> 
> Hi Mohammad,
> 
> On Fri, Apr 23, 2021 at 07:06:45AM +0800, mohammad.athari.ismail@xxxxxxxxx
> wrote:
> > From: Mohammad Athari Bin Ismail <mohammad.athari.ismail@xxxxxxxxx>
> >
> > Set VR_MII_DIG_CTRL1 bit-6(PRE_EMP) to enable pre-emption packet for
> > 10/100Mbps by default. This setting doesn`t impact pre-emption
> > capability for other speeds.
> >
> > Signed-off-by: Mohammad Athari Bin Ismail
> > <mohammad.athari.ismail@xxxxxxxxx>
> > ---
> 
> What is a "pre-emption packet"?

In IEEE 802.1 Qbu (Frame Preemption), pre-emption packet is used to differentiate between MAC Frame packet, Express Packet, Non-fragmented Normal Frame Packet, First Fragment of Preemptable Packet, Intermediate Fragment of Preemptable Packet and Last Fragment of Preemptable Packet. 

This bit "VR_MII_DIG_CTRL1 bit-6(PRE_EMP)" defined in DesignWare Cores Ethernet PCS Databook is to allow the IP to properly receive/transmit pre-emption packets in SGMII 10M/100M Modes.

Thanks.