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

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Date:   Fri, 23 Apr 2021 03:53:08 +0300
From:   Vladimir Oltean <olteanv@...il.com>
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" <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

On Fri, Apr 23, 2021 at 12:45:25AM +0000, Ismail, Mohammad Athari wrote:
> 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. 

Citation needed, which clause are you referring to?

> 
> 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.

Shouldn't everything be handled at the MAC merge sublayer? What business
does the PCS have in frame preemption?

Also, I know it's easy to forget, but Vinicius' patch series for
supporting frame preemption via ethtool wasn't accepted yet. How are you
testing this?