Re: machine_is_dt() ?

On 01/06/2013 08:08 AM, Andrew Lunn wrote:

On Sun, Jan 06, 2013 at 01:41:13PM +0000, Russell King - ARM Linux wrote:

quoted

On Sun, Jan 06, 2013 at 02:18:05PM +0100, Andrew Lunn wrote:

quoted

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.

quoted

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?

You could make the platform code create the platform device in the DT
case as well. Not all platform devices have to come from a DT node and
putting virtual devices in DT is wrong.

Rob

Thanks
	Andrew
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