Subject: Re: [PATCH] netdev/phy: add MDIO bus multiplexer driven by a memory-mapped FPGA

From: David Daney <[email-masked]>
Date: Wed, 22 Aug 2012 15:24:05 -0700

On 08/22/2012 02:45 PM, Timur Tabi wrote:
> An FPGA controls which sub-bus is connected to the master MDIO bus.  The
> FPGA must be memory-mapped and contain only 8-bit registers (which keeps
> things simple).
>
> Tested on a Freescale P5020DS board which uses the "PIXIS" FPGA attached
> to the localbus.
>
> Signed-off-by: Timur Tabi <[email-masked]>
> ---
>   .../devicetree/bindings/net/mdio-mux-fpga.txt      |   74 ++++++++
>   drivers/net/phy/Kconfig                            |   13 ++
>   drivers/net/phy/Makefile                           |    1 +
>   drivers/net/phy/mdio-mux-fpga.c                    |  186 ++++++++++++++++++++

I am fine with the general concept of the patch, so I am going to start 
a Bike Shedding session with it over the names of some of the things here.

I wonder if *fpga is really a good name for this.  It is a general 
purpose multiplexer with a memory mapped control register.  I would call 
it something like mdio-mux-mmioreg.

>   4 files changed, 274 insertions(+), 0 deletions(-)
>   create mode 100644 Documentation/devicetree/bindings/net/mdio-mux-fpga.txt
>   create mode 100644 drivers/net/phy/mdio-mux-fpga.c
>
> diff --git a/Documentation/devicetree/bindings/net/mdio-mux-fpga.txt b/Documentation/devicetree/bindings/net/mdio-mux-fpga.txt
> new file mode 100644
> index 0000000..ef567c6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/net/mdio-mux-fpga.txt
> @@ -0,0 +1,74 @@
> +Properties for an MDIO bus multiplexer/switch controlled by an FPGA register.
> +
> +This is a special case of a MDIO bus multiplexer.  An FPGA register is used
> +to control which child bus is connected.
> +
> +Required properties in addition to the generic multiplexer properties:
> +
> +- compatible : string, must contain "mdio-mux-fpga"
> +
> +- mdio-mux-device : phandle, points to the FPGA (or similar) node.  This
> +	must be a memory-mapped device with 8-bit registers.

You shouldn't need this.  Just make the multiplexer a child of FPGA node 
to indicate where it lives.

> +
> +- mdio-mux-register : integer, contains the offset of the register that
> +	controls the bus multiplexer.

This should just be the normal "reg" properly

> +
> +- mdio-mux-mask : integer, contains an 8-bit mask that specifies which
> +	bits in the register control the actual bus multiplexer.  The
> +	'reg' property of each child mdio-mux node must be constrained by
> +	this mask.
> +

"reg-mask" ??

Do you need a shift too?

David Daney