Re: [net-next PATCH v3 4/5] net: phy: Introduce fwnode_get_phy_id()

[Calvin Johnson]

On Mon, May 11, 2020 at 10:38:49AM +0100, Russell King - ARM Linux admin wrote:
> On Mon, May 11, 2020 at 01:30:40PM +0530, Calvin Johnson wrote:
> > On Sat, May 09, 2020 at 01:42:57AM +0200, Andrew Lunn wrote:
> > > On Fri, May 08, 2020 at 05:48:33PM -0500, Jeremy Linton wrote:
> > > > Hi,
> > > > 
> > > > On 5/8/20 3:27 PM, Andrew Lunn wrote:
> > > > > > > There is a very small number of devices where the vendor messed up,
> > > > > > > and did not put valid contents in the ID registers. In such cases, we
> > > > > > > can read the IDs from device tree. These are then used in exactly the
> > > > > > > same way as if they were read from the device.
> > > > > > > 
> > > > > > 
> > > > > > Is that the case here?
> > > > > 
> > > > > Sorry, I don't understand the question?
> > > > 
> > > > I was asking in general, does this machine report the ID's correctly.
> > > 
> > > Very likely, it does.
> > > 
> > > > The embedded single mac:mdio per nic case seems like the normal case, and
> > > > most of the existing ACPI described devices are setup that way.
> > > 
> > > Somebody in this thread pointed to ACPI patches for the
> > > MACCHIATOBin. If i remember the hardware correctly, it has 4 Ethernet
> > > interfaces, and two MDIO bus masters. One of the bus masters can only
> > > do C22 and the other can only do C45. It is expected that the busses
> > > are shared, not a nice one to one mapping.
> > > 
> > > > But at the same time, that shifts the c22/45 question to the nic
> > > > driver, where use of a DSD property before instantiating/probing
> > > > MDIO isn't really a problem if needed.
> > > 
> > > This in fact does not help you. The MAC driver has no idea what PHY is
> > > connected to it. The MAC does not know if it is C22 or C45. It uses
> > > the phylib abstraction which hides all this. Even if you assume 1:1,
> > > use phy_find_first(), it will not find a C45 PHY because without
> > > knowing there is a C45 PHY, we don't scan for it. And we should expect
> > > C45 PHYs to become more popular in the next few years.
> > 
> > Agree.
> > 
> > NXP's LX2160ARDB platform currently has the following MDIO-PHY connection.
> > 
> > MDIO-1 ==> one 40G PHY, two 1G PHYs(C45), two 10G PHYs(C22)
> 
> I'm not entirely sure you have that correct.  The Clause 45 register set
> as defined by IEEE 802.3 does not define registers for 1G negotiation,
> unless the PHY either supports Clause 22 accesses, or implements some
> kind of vendor extension.  For a 1G PHY, this would be wasteful, and
> likely incompatible with a lot of hardware/software.
> 
> Conversely, Clause 22 does not define registers for 10G speeds, except
> accessing Clause 45 registers indirectly through clause 22 registers,
> which would also be wasteful.
> 
Got your point.
Let me try to clarify.

MDIO-1 ==> one 40G PHY, two 1G PHYs(C45), two 10G PHYs(C22)
MDIO-2 ==> one 25G PHY
This is the physical connection of MDIO & PHYs on the platform.

For the c45 PHYs(two 10G), we use compatible "ethernet-phy-ieee802.3-c45"(not
yet upstreamed).
For c22 PHYs(two 1G), we don't mention the c45 compatible string and hence the
access also will be using c22, if I'm not wrong.

Regards
Calvin
k