netdev - Re: [PATCH 06/16] net: phy: adin: support PHY mode converters

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Date:   Wed, 7 Aug 2019 08:00:53 +0000
From:   "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>
To:     "andrew@...n.ch" <andrew@...n.ch>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: Re: [PATCH 06/16] net: phy: adin: support PHY mode converters

On Tue, 2019-08-06 at 17:39 +0200, Andrew Lunn wrote:
> [External]
> 
> On Tue, Aug 06, 2019 at 06:47:08AM +0000, Ardelean, Alexandru wrote:
> > On Mon, 2019-08-05 at 16:51 +0200, Andrew Lunn wrote:
> > > [External]
> > > 
> > > On Mon, Aug 05, 2019 at 07:54:43PM +0300, Alexandru Ardelean wrote:
> > > > Sometimes, the connection between a MAC and PHY is done via a
> > > > mode/interface converter. An example is a GMII-to-RGMII converter, which
> > > > would mean that the MAC operates in GMII mode while the PHY operates in
> > > > RGMII. In this case there is a discrepancy between what the MAC expects &
> > > > what the PHY expects and both need to be configured in their respective
> > > > modes.
> > > > 
> > > > Sometimes, this converter is specified via a board/system configuration (in
> > > > the device-tree for example). But, other times it can be left unspecified.
> > > > The use of these converters is common in boards that have FPGA on them.
> > > > 
> > > > This patch also adds support for a `adi,phy-mode-internal` property that
> > > > can be used in these (implicit convert) cases. The internal PHY mode will
> > > > be used to specify the correct register settings for the PHY.
> > > > 
> > > > `fwnode_handle` is used, since this property may be specified via ACPI as
> > > > well in other setups, but testing has been done in DT context.
> > > 
> > > Looking at the patch, you seems to assume phy-mode is what the MAC is
> > > using? That seems rather odd, given the name. It seems like a better
> > > solution would be to add a mac-mode, which the MAC uses to configure
> > > its side of the link. The MAC driver would then implement this
> > > property.
> > > 
> > 
> > actually, that's a pretty good idea;
> > i guess i was narrow-minded when writing the driver, and got stuck on phy specifics, and forgot about the MAC-side;
> > [ i also catch these design elements when reviewing, but i also seem to miss them when writing stuff sometimes ]
> > 
> 
> Hi Ardelean
> 
> We should also consider the media converter itself. It is passive, or
> does it need a driver. You seems to be considering GMII-to-RGMII. But
> what about RGMII to SGMII? or RGMII to 1000Base-KX etc? Ideally we
> want a generic solution and we need to think about all the parts in
> the system.

In our case the GMII-to-RGMII converter is passive and does not need a driver.
It's an HDL/FPGA block.
There may be other converters that do need a driver.
To be honest, the multitude of possible configurations [given that it's FPGA] can be... a lot.

In one of our cases, specifying the MAC mode to be different than PHY mode [which assumes that there is an implicit
passive media converter in-between] works.

I admit that a generic solution would be nice.
Is it ok if we defer the solution for this drivers/patchset?

If you propose something, I can take a look as part of a different/new discussion.

No guarrantees about how soon it would be implemented.

Thanks
Alex

> 
>      Andrew