Re: [PATCH v2 0/5] Generic PHY Framework

From: kishon
Date: Tue Feb 19 2013 - 06:29:36 EST


On Tuesday 19 February 2013 04:14 PM, Arnd Bergmann wrote:
On Tuesday 19 February 2013, Kishon Vijay Abraham I wrote:
Added a generic PHY framework that provides a set of APIs for the PHY drivers
to create/destroy a PHY and APIs for the PHY users to obtain a reference to
the PHY with or without using phandle. To obtain a reference to the PHY
without using phandle, the platform specfic intialization code (say from board
file) should have already called phy_bind with the binding information. The
binding information consists of phy's device name, phy user device name and an
index. The index is used when the same phy user binds to mulitple phys.

This framework will be of use only to devices that uses external PHY (PHY
functionality is not embedded within the controller).

The intention of creating this framework is to bring the phy drivers spread
all over the Linux kernel to drivers/phy to increase code re-use and to
increase code maintainability.

Comments to make PHY as bus wasn't done because PHY devices can be part of
other bus and making a same device attached to multiple bus leads to bad

How does this relate to the generic PHY interfaces in drivers/net/phy?

Currently drivers/phy and drivers/net/phy are independent and are not related to each other. There are some fundamental differences on how these frameworks work. IIUC, the *net* uses bus layer (MDIO bus) to match a PHY device with a PHY driver and the Ethernet device uses the bus layer to get the PHY.
The Generic PHY Framework however doesn't have any bus layer. The PHY should be like any other Platform Devices and Drivers and the framework will provide some APIs to register with the framework. And there are other APIs which any controller can use to get the PHY (for e.g., in the case of dt boot, it can use phandle to get a reference to the PHY).

Do you expect that to get merged into drivers/phy in the long run, or
do you want to keep the generic phy only for everything but ethernet?

We'd like the PHY drivers spread all over the kernel to get merged to drivers/phy including Ethernet. Having said that, Ethernet itself has a huge PHY framework and it's going to be little challenging to adapt to the new PHY framework (of course there'll be changes in this PHY framework when we want to have network PHY added here). But adapting USB PHYs to the new framework will be simpler and will be taken first. Also when we add SATA PHY (OMAP5), it will make use of this framework as both SATA and USB3 uses the same PHY IP.

I think it would be problematic to have two alternative interfaces for
ethernet PHYs because then an ethernet driver still needs to decide
which subsystem to interface with.

Right. For now Ethernet should continue to use their own PHY abstraction layer till we are a bit more clear on how to move it to drivers/phy.

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