[PATCH net-next 1/2] dt-bindings: net: xlnx,axi-ethernet: Add bindings for AXI 2.5G MAC

[Gupta, Suraj]

> -----Original Message-----
> From: Andrew Lunn <andrew at lunn.ch>
> Sent: Tuesday, November 19, 2024 7:09 AM
> To: Sean Anderson <sean.anderson at linux.dev>
> Cc: Maxime Chevallier <maxime.chevallier at bootlin.com>; Gupta, Suraj
> <Suraj.Gupta2 at amd.com>; andrew+netdev at lunn.ch; davem at davemloft.net;
> edumazet at google.com; kuba at kernel.org; pabeni at redhat.com; Simek, Michal
> <michal.simek at amd.com>; Pandey, Radhey Shyam
> <radhey.shyam.pandey at amd.com>; horms at kernel.org; netdev at vger.kernel.org;
> linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org; git (AMD-Xilinx)
> <git at amd.com>; Katakam, Harini <harini.katakam at amd.com>
> Subject: Re: [PATCH net-next 1/2] dt-bindings: net: xlnx,axi-ethernet: Add bindings
> for AXI 2.5G MAC
> 
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> 
> On Mon, Nov 18, 2024 at 10:57:45AM -0500, Sean Anderson wrote:
> > On 11/18/24 10:54, Maxime Chevallier wrote:
> > > Hello,
> > >
> > > On Mon, 18 Nov 2024 13:48:21 +0530
> > > Suraj Gupta <suraj.gupta2 at amd.com> wrote:
> > >
> > >> AXI 1G/2.5G Ethernet subsystem supports 1G and 2.5G speeds. "max-speed"
> > >> property is used to distinguish 1G and 2.5G MACs of AXI 1G/2.5G IP.
> > >> max-speed is made a required property, and it breaks DT ABI but
> > >> driver implementation ensures backward compatibility and assumes 1G
> > >> when this property is absent.
> > >> Modify existing bindings description for 2.5G MAC.
> > >
> > > That may be a silly question, but as this is another version of the
> > > IP that behaves differently than the 1G version, could you use
> > > instead a dedicated compatible string for the 2.5G variant ?
> > >
> > > As the current one is :
> > >
> > > compatible = "xlnx,axi-ethernet-1.00.a";
> > >
> > > it seems to already contain some version information.
> > >
> > > But I might also be missing something :)
> >
> > As it happens, this is not another version of the same IP but a
> > different configuration. It's just that no one has bothered to add
> > 2.5G support yet.
> 
> Do you mean 2.5G is a synthesis option? Or are you saying it has always been able
> to do 2.5G, but nobody has added the needed code?
> 
> This is a pretty unusual use of max-speed, so i would like to fully understand why it
> is being used before allowing it.
> 
>         Andrew

2.5G support was already there in hardware, driver is getting upstream now. 1G or 2.5G configuration needs to be selected before synthesis. In 2.5G configuration it supports only 2.5G speed.
I'm exploring registers to get 1G / 2.5G selections information instead of using max-speed. Will send next series soon.

Just for my understanding, could you please share the use of max-speed DT property if possible?