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Date:   Mon, 3 Aug 2020 11:45:55 +0000
From:   "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>
CC:     Andrew Lunn <andrew@...n.ch>,
        Vikas Singh <vikas.singh@...esoftware.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Calvin Johnson (OSS)" <calvin.johnson@....nxp.com>,
        kuldip dwivedi <kuldip.dwivedi@...esoftware.com>,
        Vikas Singh <vikas.singh@....com>
Subject: RE: [PATCH 2/2] net: phy: Associate device node with fixed PHY

> -----Original Message-----
> From: Russell King - ARM Linux admin <linux@...linux.org.uk>
> Sent: 03 August 2020 12:07
> To: Madalin Bucur (OSS) <madalin.bucur@....nxp.com>
> Cc: Andrew Lunn <andrew@...n.ch>; Vikas Singh
> <vikas.singh@...esoftware.com>; f.fainelli@...il.com; hkallweit1@...il.com;
> netdev@...r.kernel.org; Calvin Johnson (OSS) <calvin.johnson@....nxp.com>;
> kuldip dwivedi <kuldip.dwivedi@...esoftware.com>; Vikas Singh
> <vikas.singh@....com>
> Subject: Re: [PATCH 2/2] net: phy: Associate device node with fixed PHY
> 
> On Mon, Aug 03, 2020 at 08:33:19AM +0000, Madalin Bucur (OSS) wrote:
> > > -----Original Message-----
> > > From: netdev-owner@...r.kernel.org <netdev-owner@...r.kernel.org> On
> > > Behalf Of Andrew Lunn
> > > Sent: 01 August 2020 18:11
> > > To: Russell King - ARM Linux admin <linux@...linux.org.uk>
> > > Cc: Vikas Singh <vikas.singh@...esoftware.com>; f.fainelli@...il.com;
> > > hkallweit1@...il.com; netdev@...r.kernel.org; Calvin Johnson (OSS)
> > > <calvin.johnson@....nxp.com>; kuldip dwivedi
> > > <kuldip.dwivedi@...esoftware.com>; Madalin Bucur (OSS)
> > > <madalin.bucur@....nxp.com>; Vikas Singh <vikas.singh@....com>
> > > Subject: Re: [PATCH 2/2] net: phy: Associate device node with fixed
> PHY
> > >
> > > On Sat, Aug 01, 2020 at 10:41:32AM +0100, Russell King - ARM Linux
> admin
> > > wrote:
> > > > On Sat, Aug 01, 2020 at 09:52:52AM +0530, Vikas Singh wrote:
> > > > > Hi Andrew,
> > > > >
> > > > > Please refer to the "fman" node under
> > > > > linux/arch/arm64/boot/dts/freescale/fsl-ls1046a-rdb.dts
> > > > > I have two 10G ethernet interfaces out of which one is of fixed-
> link.
> > > >
> > > > Please do not top post.
> > > >
> > > > How does XGMII (which is a 10G only interface) work at 1G speed?  Is
> > > > what is in DT itself a hack because fixed-phy doesn't support 10G
> > > > modes?
> > >
> > > My gut feeling is there is some hack going on here, which is why i'm
> > > being persistent at trying to understand what is actually going on
> > > here.
> >
> > Hi Andrew,
> >
> > That platform used 1G fixed link there since there was no support for
> > 10G fixed link at the time. PHYlib could have tolerated 10G speed there
> > With a one-liner.
> 
> That statement is false.  It is not a "one liner".  fixed-phy exposes
> the settings to userspace as a Clause 22 PHY register set, and the
> Clause 22 register set does not support 10G.  So, a "one liner" would
> just be yet another hack.  Adding Clause 45 PHY emulation support
> would be a huge task.
> 
> > I understand that PHYLink is working to describe this
> > Better, but it was not there at that time. Adding the dependency on
> > PHYLink was not desirable as most of the users for the DPAA 1 platforms
> > were targeting kernels before the PHYLink introduction (and last I've
> > looked, it's still under development, with unstable APIs so we'll
> > take a look at this later, when it settles).
> 
> I think you need to read Documentation/process/stable-api-nonsense.rst
> particularly the section "Stable Kernel Source Interfaces".
> 
> phylink is going to be under development for quite some time to come
> as requirements evolve.  For example, when support for QSFP interfaces
> is eventually worked out, I suspect there will need to be some further
> changes to the driver interface.  This is completely normal.
> 
> Now, as to the stability of the phylink API to drivers, it has in fact
> been very stable - it has only changed over the course of this year to
> support split PCS, a necessary step for DPAA2 and a few others.  It has
> been around in mainline for two years, and has been around much longer
> than that, and during that time it has been in mainline, the MAC facing
> interface has not changed until recently.
> 
> So, I find your claim to be quite unreasonable.
> 
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

I see you agree that there were and there will be many changes for a while,
It's not a complaint, I know hot it works, it's just a decision based on
required effort vs features offered vs user requirements. Lately it's been
time consuming to try to fix things in this area.

Regards
Madalin

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