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SubjectRe: [PATCH 2/3] arm64: dts: add the Alpine v2 EVP
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On 09/02/16 10:13, Tsahee Zidenberg wrote:
> 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.

That's quite sad indeed. You are pointlessly breaking existing software.
But hey, that's your choice. At that point, I can't be bothered to care.

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

Well, at least you'll be able to run GICv3 guests, assuming everything
else is usable.

M.
--
Jazz is not dead. It just smells funny...

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