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

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Date:   Fri, 23 Apr 2021 00:45:25 +0000
From:   "Ismail, Mohammad Athari" <mohammad.athari.ismail@...el.com>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S . Miller" <davem@...emloft.net>,
        "Jakub Kicinski" <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "Ong, Boon Leong" <boon.leong.ong@...el.com>,
        "Voon, Weifeng" <weifeng.voon@...el.com>,
        "Wong, Vee Khee" <vee.khee.wong@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 net-next] net: pcs: Enable pre-emption packet for
 10/100Mbps

Hi Vladimir,

> -----Original Message-----
> From: Vladimir Oltean <olteanv@...il.com>
> Sent: Friday, April 23, 2021 7:53 AM
> To: Ismail, Mohammad Athari <mohammad.athari.ismail@...el.com>
> Cc: Alexandre Torgue <alexandre.torgue@...com>; Jose Abreu
> <joabreu@...opsys.com>; David S . Miller <davem@...emloft.net>; Jakub
> Kicinski <kuba@...nel.org>; Andrew Lunn <andrew@...n.ch>; Heiner Kallweit
> <hkallweit1@...il.com>; Russell King <linux@...linux.org.uk>; Ong, Boon
> Leong <boon.leong.ong@...el.com>; Voon, Weifeng
> <weifeng.voon@...el.com>; Wong, Vee Khee <vee.khee.wong@...el.com>;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org
> 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@...el.com
> wrote:
> > From: Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>
> >
> > 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@...el.com>
> > ---
> 
> 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.