[PATCH v2 7/8] net: mvmdio: add xmdio support

Hi Andrew,

On Fri, Jun 09, 2017 at 04:49:36PM +0200, Andrew Lunn wrote:

On Fri, Jun 09, 2017 at 04:09:22PM +0200, Antoine Tenart wrote:

quoted

The MDIO/xMDIO registers are embedded into the network controller. The
mvmdio driver was created at first to abstract this functionality
outside the network controller driver because it is shared between all
ports and used in different IPs. So it's not really devices per say.

Looking at the datasheet/schematics there are two hardware buses, one
for c22 and one for c45. So we should keep two separate nodes to
describe the two interfaces. From what I read c45 is backward
compatible with c22 so the xSMI interface should be capable to speak to
c22 PHYs as well.

The on the wire protocol of c45 is backwards compatible with c22, in
that a c22 device will not get confused by a c45 transaction on the
bus. A c22 device will just ignore it. You cannot talk to a c22 device
using c45.

I see.

From what you are saying, you have a hardware block generating c45
transactions and a hardware block which generates c22 transactions.
What is not clear to me is if these two hardware blocks are using the
same physical MDC/MDIO pins, i.e. there is just one MDIO bus to the
outside world, or are there two busses?

There are two busses, one generating c22 transactions and one generating
c45 transactions. Each bus has its own MDC/MDIO pins.

quoted

And by looking at the datasheet this seems possible, although it's
not completely clear. But anyway this wouldn't impact the dt
bindings.

What i'm worried about is there being one set of MDC/MDIO lines. You
should not expose that to linux as two mdio busses. It is one bus.

The phylib will poll each phy on the bus once per second to check its
state. The phylib serialises the read/writes at a bus level. So if you
have one physical bus registered as two logical bus, at some point you
are going to get simultaneous read/writes, and you are going to need a
mutex low down to serialise this for physical bus access.

And in the end, this would affect the dt binding. If it is one
physical bus, you want one binding representing both c22 and c45
transactions.

Of course. See above.

Thanks!
Antoine

-- 
Antoine T?nart, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20170609/a03cf96d/attachment.sig>