linux-kernel - Re: [PATCH net-next 4/4] net: dsa: microchip: add SGMII port support to KSZ9477 switch

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Message-ID: <2f59b854-c1d4-4007-bc6e-4c8e88eda940@lunn.ch>
Date: Sat, 10 Aug 2024 19:52:33 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Tristram.Ha@...rochip.com
Cc: Woojung Huh <woojung.huh@...rochip.com>, UNGLinuxDriver@...rochip.com,
	devicetree@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Marek Vasut <marex@...x.de>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 4/4] net: dsa: microchip: add SGMII port support
 to KSZ9477 switch

On Fri, Aug 09, 2024 at 04:38:40PM -0700, Tristram.Ha@...rochip.com wrote:
> From: Tristram Ha <tristram.ha@...rochip.com>
> 
> The SGMII module of KSZ9477 switch can be setup in 3 ways: 0 for direct
> connect, 1 for 1000BaseT SFP, and 2 for 10/100/1000 SFP.
> 
> SFP is typically used so the default is 1.  The driver can detect
> 10/100/1000 SFP and change the mode to 2.  For direct connect this mode
> has to be explicitly set to 0 as driver cannot detect that
> configuration.
> 
> The SGMII module can only report basic link status of the SFP, so it is
> simulated as a regular internal PHY.
> 
> Since the regular PHY in the switch uses interrupt instead of polling the
> driver has to handle the SGMII interrupt indicating link on/off.
> 
> One issue for the 1000BaseT SFP is there is no link down interrupt, so
> the driver has to use polling to detect link down when the link is up.
> 
> Recent change in the DSA operation can setup the port before the PHY
> interrupt handling function is registered.  As the SGMII interrupt can
> be triggered after port setup there is extra code in the interrupt
> processing to handle this situation.  Otherwise a kernel fault can be
> triggered.
> 
> Note the SGMII interrupt cannot be masked in hardware.  Also the module
> is not reset when the switch is reset.  It is important to reset the
> module properly to make sure the interrupt is not triggered prematurely.

Why not model this as a PCS? Russell has been converting all PCS like
things in DSA into try PCS drivers. So i suspect Russell will not like
this code, and would prefer a PCS driver.

	Andrew