netdev - Re: [PATCH net-next v4 1/2] net: dsa: microchip: ksz8: Make flow control, speed, and duplex on CPU port configurable

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Message-ID: <20230520050317.GC18246@pengutronix.de>
Date: Sat, 20 May 2023 07:03:17 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Woojung Huh <woojung.huh@...rochip.com>, Andrew Lunn <andrew@...n.ch>,
	Arun Ramadoss <arun.ramadoss@...rochip.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Simon Horman <simon.horman@...igine.com>,
	"Russell King (Oracle)" <linux@...linux.org.uk>,
	linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>, kernel@...gutronix.de,
	netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
	UNGLinuxDriver@...rochip.com,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next v4 1/2] net: dsa: microchip: ksz8: Make flow
 control, speed, and duplex on CPU port configurable

On Fri, May 19, 2023 at 11:34:49PM +0300, Vladimir Oltean wrote:
> On Fri, May 19, 2023 at 08:50:15PM +0200, Oleksij Rempel wrote:
> > Thank you for your feedback. I see your point. 
> > 
> > We need to remember that the KSZ switch series has different types of
> > ports. Specifically, for the KSZ8 series, there's a unique port. This
> > port is unique because it's the only one that can be configured with
> > global registers, and it is only one supports tail tagging. This special
> > port is already referenced in the driver by "dev->cpu_port", so I continued
> > using it in my patch.
> 
> Ok, I understand, so for the KSZ8 family, the assumption about which
> port will use tail tagging is baked into the hardware.
> 
> > It is important to note that while this port has an xMII interface, it
> > is not the only port that could have an xMII interface. Therefore, using
> > "dev->info->internal_phy" may not be the best way to identify this port,
> > because there can be ports that are not global/cpu, have an xMII
> > interface, but don't have an internal PHY.
> 
> Right, but since we're talking about phylink, the goal is to identify
> the xMII ports, not the CPU ports... This is a particularly denatured
> case because the xMII port is global and is also the CPU port.

I see. Do you have any suggestions for a better or more suitable
implementation? I'm open to ideas.

Regards,
Oleksij
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