Re: machine_is_dt() ?

[Andrew Lunn <andrew-g2DYL2Zd6BY@public.gmane.org>]

On Sun, Jan 06, 2013 at 01:41:13PM +0000, Russell King - ARM Linux wrote:
> On Sun, Jan 06, 2013 at 02:18:05PM +0100, Andrew Lunn wrote:
> > I'm moving the cpuidle code for Kirkwood into drivers/cpuidle. I'm
> > following the way cpuidle-calxeda.c instantiates the driver, it uses
> > module_init(calxeda_cpuidle_init) and calxeda_cpuidle_init() uses
> > of_machine_is_compatible("calxeda,highbank") so only loading the
> > driver in a ARCH_MULTIPLATFORM kernel when needed.
> > 
> > I can follow this model for when kirkwood is booted using device
> > tree. However, i would also like to use the driver for those boards
> > which are not yet converted to DT. In that situation, we have a kernel
> > dedicate to kirkwood and the cpuidle driver is always relevant.
> > 
> > Thus i need to code something like:
> > 
> > (of_machine_is_compatible("marvell, kirkwood") ||
> >  !machine_is_dt())
> > 
> > However, there is no macro machine_is_dt().
> > 
> > Is there a way to tell if a machine has been booted using a machine
> > number as opposed to DT?
> 
> This doesn't seem to me to be the right way to deal with this.  What
> you're suggesting would mean that if you built a multiplatform kernel
> which included this driver, and booted it on a non-DT platform, you'd
> have this driver registered.

Hi Russel

Yes, not what i want. I would need to limit it further to non-DT
platform on Kirkwood.

> It looks to me like many of the CPUFREQ drivers just register themselves
> if they've been built into the kernel.  No one's thought about making
> them platform drivers or similar, so the current "if it's built-in, then
> we use it" approach seems to have persisted.  As many of them are
> initialized via a late_initcall(), I don't see any problem with them
> being platform drivers, which will solve the problem in a way that's
> well established.
I actually went towards a platform driver to start with. See the
discussion here:

https://patchwork.kernel.org/patch/1915171/

About 1/2 way down, Rob Herring says:

      Don't do a platform driver and just check the machine compatible
      property which is what I did for highbank.

What Rob mostly seems to be objecting to is that

+		cpuidle@1418 {
+			compatible = "marvell,kirkwood-cpuidle";
+			reg = <0x1418 0x4>;
+		};

does not describe hardware, so it does not belong in DT. Hence i will
check of_machine_is_compatible() to see if its a marvell,kirkwood. But
that does not help with old style boots.

Should i make it both a platform driver for old style boots and check
of_machine_is_compatible() for DT boots?

Thanks
	Andrew