RE: RFC: top level compatibles for virtual platforms

[Yoder Stuart-B08248 <B08248@freescale.com>]

> -----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 <timur@freescale.com> wrote:
>=20
> > >> 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