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

[Vladimir Oltean]

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

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?