Re: [PATCH v2 00/16] ARM: support for ICP DAS LP-8x4x (with dts)

Arnd Bergmann
2013-12-19T05:30:42Z

On Wednesday 18 December 2013, Sergei Ianovich wrote:
> > You would still be able to boot a kernel with an old dts file on a new
> > kernel if it just contains a "simple-bus" node here, as long as it doesn't
> > need any boot-time setup at the bus controller. We can change the dts
> > file later if we need to add this functionality, which would break booting
> > old kernels with the new dts files, which isn't much of a problem in
> > general.
>
> It should actually only break old kernels which require new
> functionally. Otherwise, dts can have
>
> compatible = "marvell,pxa-extbus", "simple-bus";
>
> and an older kernel will be happy with "simple-bus". Please correct me
> if I'm wrong.

This would work only if we can probe the devices behind the external
bus controller before the controller itsef has been set up, since
the initialization order can depend on a number of things but not
the bus hierarchy. It will also work if the code setting up the
bus controller can be guaranteed to run before we call
of_platform_populate for the regular devices, which is probably
the best solution here.

Arnd