linux-kernel - Re: [PATCH 3/3] net: phy: mediatek: add support for built-in 2.5G ethernet PHY on MT7988

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Date: Wed, 8 May 2024 17:21:11 +0100
From: Daniel Golle <daniel@...rotopia.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: SkyLake Huang (黃啟澤) <SkyLake.Huang@...iatek.com>,
	"linux@...linux.org.uk" <linux@...linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"dqfext@...il.com" <dqfext@...il.com>,
	Steven Liu (劉人豪) <steven.liu@...iatek.com>,
	"matthias.bgg@...il.com" <matthias.bgg@...il.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"hkallweit1@...il.com" <hkallweit1@...il.com>,
	"angelogioacchino.delregno@...labora.com" <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH 3/3] net: phy: mediatek: add support for built-in 2.5G
 ethernet PHY on MT7988

On Wed, May 08, 2024 at 02:30:21PM +0200, Andrew Lunn wrote:
> > I'm not sure I really get this. MT7988's internal 2.5Gphy is built
> > inside SoC. We won't have a number of these PHYs.
> 
> How long does firmware download take? If you are holding RTNL you are
> blocking all other network configuration. How many Ethernets does this
> device have? If it is just one, it is not too bad, but if there is a
> built in switch, you cannot be configuring that switch at the same
> time firmware download is happening...

The MT7988 SoC has a bunch of network interfaces:

 - GMAC0 is typically connected as conduit to a 4-port MT7530-like DSA
   switch offering 4 1GE user ports. PHY driver mediatek-ge-soc.c takes
   care of those, and yes, they do need some "care"...

 - GMAC1 can be used with the internal 2.5GE PHY (ie. with the driver
   discussed here) OR for to connect an external PHY or SFP via
   1000Base-X, 2500Base-X, SGMII, 5GBase-R, 10GBase-R or USXGMII.

 - GMAC2 is can only be used with an external PHY or SFP using
   1000Base-X, 2500Base-X, SGMII, 5GBase-R, 10GBase-R or USXGMII.

So while there is only exactly one of the internal 2.5GE PHY there are
many other network interfaces on that same SoC.

I hope that clarifies things a bit.