Re: [PATCH 2/3] arm64: dts: add the Alpine v2 EVP

[Tsahee Zidenberg]

On 9 February 2016 at 13:48, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
> On 09/02/16 10:13, Tsahee Zidenberg wrote:
>> On 9 February 2016 at 11:30, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
>>>
>>> On 09/02/16 09:14, Tsahee Zidenberg wrote:
>>>>
>>>>
>>>> On 9 February 2016 at 11:09, Marc Zyngier <marc.zyngier@xxxxxxx
>>>> <mailto:marc.zyngier@xxxxxxx>> 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.
>
> Just to make sure you are not missing the point: ARE==1 does *not* mean
> that GICV is unusable. Quite the opposite. It only makes it illegal to
> use GICC and GICH, but leaves GICV usable for a guest.
>
> So the real question is: do you have any additional HW that would
> actively prevent GICV from being used? If the answer to that is "no",
> and assuming your GICv3 implementation is compliant with the
> architecture, then GICV will be usable, and you should document all 3
> regions.
>

O.K. will add to next version.

> Thanks,
>
>         M.
> --
> Jazz is not dead. It just smells funny...