[PATCH v3 0/7] mv643xx.c: Add basic device tree support.

On 10/08/12 11:49, Arnd Bergmann wrote:

On Thursday 09 August 2012, Ian Molton wrote:

quoted

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 The driver
already knows all those offsets and they are always the same
for all variants of mv643xx, right?

Yes, but its not clean. And no amount of refactoring is
really going to make a nice driver that also fits the ancient
(and badly thought out) OF bindings.

In what way is it badly though out, or not clean? The use of
underscores in the properties, and the way that the sram
is configured is problematic, I agree. But The way that
the three ports are addressed and how the PHY is found
seems quite clever.

It forces one to load the MDIO driver first, because it maps ALL the
registers for both itself and all the ports, and the MDIO driver has no
way of knowing how many ethernet blocks are present (I have a device
here with two, and another with four). Thats anywhere from 1 to 12
ports, split across 1 to 4 address ranges, and theres a big gap in the
address range between controllers 0,1 and 2,3. *ALL* the devices on the
board are sharing ethernet block 0's MDIO bus. By pure luck it happens
to work, because the blocks 2,3 have an alias of the MDIO registers from
blocks 0,1.

Having the MDIO driver map the ethernet drivers memory is a terrible
solution, IMO. Ethernet drivers should map their own memory, and that
introduces the n-ports-per-block problem, because their address ranges
overlap.

I think the best solution is to make each ethernet block register 3 ports.

the PPC code can simply generate different fixups so that instead of
creating 3 devices, it creates one, with three ports.

quoted

If we have to break things, we can at least go for a nice
clean design, surely?

The ports arent really child devices of the MAC. The MAC
just has 3 ports.

I don't see the difference between those two things.

The ports are at best 'pseudodevices'. Real devices have registers of
their own.

quoted

We're going to have to maintain a legacy
platform_device -> DT bindings hack somewhere anyway,
at least until the remaining other users of the driver
convert to D-T.

I don't understand why you describe the method used in
powerpc as a hack. It was the normal way to introduce
DT support for platform devices back when it was implemented.

Just because its normal doesn't mean its not a hack :)

It also had the advantage of not requiring any modifications
to the generic driver, because it was shared between one
architecture using DT (powerpc) and one that didn't (ARM).

It /did/ spawn a pretty hideous driver, though...

-Ian