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SubjectRe: [PATCH 2/3] arm64: dts: add the Alpine v2 EVP
On 9 February 2016 at 11:30, Marc Zyngier <marc.zyngier@arm.com> wrote:
>
> On 09/02/16 09:14, Tsahee Zidenberg wrote:
> >
> >
> > On 9 February 2016 at 11:09, Marc Zyngier <marc.zyngier@arm.com
> > <mailto:marc.zyngier@arm.com>> wrote:
> >
> > On 09/02/16 09:01, Antoine Tenart wrote:
> > > On Tue, Feb 09, 2016 at 09:56:33AM +0100, Antoine Tenart wrote:
> > >> Hi Marc,
> > >>
> > >> On Mon, Feb 08, 2016 at 03:29:33PM +0000, Marc Zyngier wrote:
> > >>> On 08/02/16 09:11, Antoine Tenart wrote:
> > >>>
> > >>>> + gic: gic@f0100000 {
> > >>>> + compatible = "arm,gic-v3";
> > >>>> + reg = <0x0 0xf0200000 0x0 0x10000>, /* GIC Dist */
> > >>>> + <0x0 0xf0280000 0x0 0x200000>, /* GICR */
> > >>>> + <0x0 0xf0100000 0x0 0x2000>; /* GICC */
> > >>>> + interrupt-controller;
> > >>>> + #interrupt-cells = <3>;
> > >>>> + };
> > >>>
> > >>> Something is wrong here. Either you are missing GICH and GICV (assuming
> > >>> you have legacy support), or you have an extra GICC region (which
> > >>> doesn't make sense on its own).
> > >>
> > >> I'll add the missing regions.
> > >
> > > Hmm, in fact the GICC region shouldn't be there. I'll make some tests
> > > and remove it.
> >
> > If you have a GICv3 with legacy support, you will probably have GICC,
> > GICH and GICV. Linux itself will only use GICD and GICR, but it needs at
> > least GICV to be able to virtualize GICv2 guests. And GICV is not
> > allowed to exist without GICC and GICH, so I really recommend that you
> > keep GICC around.
> >
> >
> > We use the GIC without legacy support (we disable it in early boot
> > stages), so I think removing the GICC region is the better solution.
>
> Disabling legacy support doesn't mean that:
> - the HW isn't present
> - the associated regions are not useful
>
By "disabling lecgacy support in early boot" I don't just mean that
ARE bit will be set, but it will actually be RAO/WI. There will be no
way for SW to enable it and use these registers (which, sadly, means
that there will be no way to enable gicv2 virtualization). If you
insist - I will dig up the supposed location of GICV and GICH - yet it
will be both untested and entirely unusable.

We will add an entry for the maintenance interrupt, as it really can
be used by future configurations.

> Here, we describe the HW, not the usage you make of it.
>
> And unless you think that having working virtualization is completely
> useless, I strongly suggest that you properly document the HW in the
> device tree.
>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...

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