RE: RFC: top level compatibles for virtual platforms

-----Original Message-----
From: Wood Scott-B07421
Sent: Monday, July 11, 2011 11:24 AM
To: Tabi Timur-B04825
Cc: Yoder Stuart-B08248; Grant Likely; Benjamin Herrenschmidt; Gala Kumar=

-B11780; Wood Scott-

B07421; Alexander Graf; linuxppc-dev@ozlabs.org
Subject: Re: RFC: top level compatibles for virtual platforms
=20
On Mon, 11 Jul 2011 10:45:47 -0500
Timur Tabi [off-list ref] wrote:
=20

quoted

quoted

quoted

Also, if these are KVM creations, shouldn't there be a "kvm" in the
compatible string somewhere?

There is nothing KVM specific about these platforms.  Any hypervisor
could create a similar virtual machine.

True, but I think we're on a slippery slope, here.  Virtualization
allows us to create "virtual platforms" that are not well defined.
Linux requires a unique compatible string for each platform.

=20
The device tree is supposed to describe the hardware (virtual or otherwis=

e), not just supply

what Linux wants.  Perhaps there simply shouldn't be a toplevel compatibl=

e if there's nothing

appropriate to describe there -- and fix whatever issues Linux has with t=

hat.

But there is a concept in Linux of a platform 'machine':

define_machine(p4080_ds) {
        .name                   =3D "P4080 DS",
        .probe                  =3D p4080_ds_probe,
        .setup_arch             =3D corenet_ds_setup_arch,
        .init_IRQ               =3D corenet_ds_pic_init,
#ifdef CONFIG_PCI
        .pcibios_fixup_bus      =3D fsl_pcibios_fixup_bus,
#endif
        .get_irq                =3D mpic_get_coreint_irq,
        .restart                =3D fsl_rstcr_restart,
        .calibrate_decr         =3D generic_calibrate_decr,
        .progress               =3D udbg_progress,
};

Right now p4080_ds_probe needs something to match on to determine
whether this is the machine type.   How would it work if=20
there was no top level compatible to match on?   Some=20
platforms (e.g. e500v2-type) need mpc85xx_ds_pic_init(),
others need corenet_ds_pic_init().  We need a way to
select the machine.

Stuart