Re: [PATCH] Add AMCC Arches 460GT eval board support to platforms/44x

On Thu, 2008-07-17 at 00:58 +0200, Arnd Bergmann wrote:

On Wednesday 16 July 2008, Grant Likely wrote:

quoted

quoted

Shouldn't it be enough to have a common compatible value in each
of these boards, e.g. "amcc,generic-ppc44x" and then just ignore the
specific type unless you need to do something special?

This is bad for the same reason that "amcc,44x-<blah>" compatible values
are bad in device nodes.  The definition of '*-44x-*' changes over time as
new parts are added.  Compatible values should always reflect an exact
part number.

I agree in general, but I also think that all 44x boards should be
regarded as the same machine time, in the same way that all powermacs
are detected as compatible with "Power Macintosh" or "MacRISC", or
how all sorts of serial ports claim compatibility with i8250.

For classic SOCs like 4xx or 52xx, the SOC familiy more or less defines
the platform, and all the details about peripherals can be expressed
in the device tree elsewhere.

This is what Grant has done for 52xx and what I was talking about with
"4xx_board.c", though 4xx_soc.c is probably a better name.

My hesitation is that while it's true today that 440<chip name> defines
the SoC, it might not always be.  And the Virtex boards are craziness
with the core and FPGA setup.  So we need to be careful a bit when
chosing what do "bind" to for generics.

If one board is so different that you need a separate board setup
in the kernel, it should simply not claim compatibility with the
SOC platform.

Right.  Today we only have a few "overrides" in 4xx.  Namely
Canyonlands/Glacier, and Bamboo/Yosemite (Sequoia/Rainier should also
really be that way, but they aren't).  So if we decide to go to a
different scheme, it shouldn't be a big deal to switch.

josh