[PATCH 7/7] commands: Add mdio_read and mdio_write

[Andrey Smirnov]

On Tue, Jan 26, 2016 at 1:55 PM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> On Mon, Jan 25, 2016 at 09:55:58PM -0800, Andrey Smirnov wrote:
>> Add commands for low-level access to MDIO bus.
>
> Do we really need this? We can already read/write phy registers using
> /dev/phyx which imo is quite convenient since it can be accessed with
> regular md/mw commands.
>
> This of course is currently limited to the phys that are actually
> registered, you can't just bang on MDIO addresses on which no phys are
> registered. Maybe we could register all phys on a MDIO bus instead of
> only the used ones?

Just to explain the purpose of this patch -- there are number of
reasons we might want to be able to access "unregistered" PHYs:

- Not all MDIO attached devices would have PHYSID1,2 registers
available which might cause mdiobus_scan() to not detect those PHYs

- MDIO bus troubleshooting

As for registering all PHYs on a bus, correct me if I am wrong but
that would result in 32*N number of entries in /dev, where N is number
of MDIO buses in the system. The device I am working with right now
has 3 MDIO buses which would mean that I'd end up with 96 additional
entries in /dev, which might be a little bit overwhelming from UI
point of view. The other UI problem with that approach is that
/dev/phy's are numbered linearly so in order to figure out how to
access device on bus N at address M, user would have to perform N*32 +
M in their head.

Andrey