[PATCH] arm64: dts: Fix GIC reg sizes for APM X-Gene

Marc Zyngier marc.zyngier at arm.com
Thu Mar 19 11:54:53 PDT 2015

On 24/02/15 06:34, Pranavkumar Sawargaonkar wrote:
> Hi Rob,
> On Mon, Feb 23, 2015 at 10:09 PM, Rob Herring <robherring2 at gmail.com> wrote:
>> On Mon, Feb 23, 2015 at 6:07 AM, Christoffer Dall
>> <christoffer.dall at linaro.org> wrote:
>>> On Sat, Feb 21, 2015 at 03:56:17PM -0600, Rob Herring wrote:
>>>> On Thu, Feb 19, 2015 at 1:03 PM, Christoffer Dall
>>>> <christoffer.dall at linaro.org> wrote:
>>>>> On Thu, Feb 19, 2015 at 12:23:15PM -0600, Rob Herring wrote:
>>>>>> On Tue, Jan 27, 2015 at 1:03 AM, Pranavkumar Sawargaonkar
>>>>>> <psawargaonkar at apm.com> wrote:
>>>>>>> In APM X-Gene, GIC register space is 64K aligned while the sizes mentioned
>>>>>>> in the dt are 4K aligned. This breaks KVM when kernel is built with 64K page
>>>>>>> size due to size alignment checking in vgic driver for VCPU Control and
>>>>>>> VCPU register.
>>>>>>> This patch corrects the sizes to be inline with the hardware spec.
>>>>>> This does not make sense. The GIC regions are still only 4 or 8KB and
>>>>>> the h/w description should reflect that. For implementations using
>>>>>> gic-400 and the addressing decode trick, the rest of the register
>>>>>> range is also not safe to access given it is multiple mapped. Also,
>>>>>> this wastes virtual space, but I guess we don't care on 64-bit.
>>>>>> KVM should be fixed to only check base address alignment. Size
>>>>>> alignment does not matter (if it does, then you need to fix all
>>>>>> register blocks).
>>>>> It matters if you want to ensure that the 64K page you are assigning to
>>>>> a guest for the GIC virtual CPU interface contains only GIC virtual CPU
>>>>> mappings, and not other random stuff that the guest is not allowed to
>>>>> touch.
>>>> Good point.
>>>>> How else should this be enforced?
>>>> Rely on correct h/w design? You'll have to repeat this every time you
>>>> want to do pass-thru of a device.
>>>> What do you do if 64K mapping is not supported? Fallback to emulation
>>>> of the CPU interface?
>>> Agree with Peter on these two points.
>>>> Are there other DTSs that need to be fixed?
>>> Not sure really, AMD Seattle works with 64K pages IIRC.
>> Well, looks we have been inconsistent here:
>> arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-           reg = <0x0
>> 0xe1110000 0 0x1000>,
>> arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-                 <0x0
>> 0xe112f000 0 0x2000>,
>> arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-                 <0x0
>> 0xe1140000 0 0x10000>,
>> arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-                 <0x0
>> 0xe1160000 0 0x10000>;
>> arch/arm64/boot/dts/arm/juno.dts-               reg = <0x0 0x2c010000 0 0x1000>,
>> arch/arm64/boot/dts/arm/juno.dts-                     <0x0 0x2c02f000 0 0x2000>,
>> arch/arm64/boot/dts/arm/juno.dts-                     <0x0 0x2c04f000 0 0x2000>,
>> arch/arm64/boot/dts/arm/juno.dts-                     <0x0 0x2c06f000 0 0x2000>;
>> If we are going to use 64K sizes, can we have some consistency here
>> please. Which ranges really need 64KB sizes? It should only be the
>> VCPU interface. right? Why does XGene need 128K? If XGene is doing
>> address swizzling, then the CPU and VCPU base addresses are wrong.
>> Seattle is also wrong for the VCPU, but no one has noticed because we
>> don't use the DIR register IIRC.
>> XGene should also add an "arm,gic-400" compatible string or something
>> XGene specific if in fact it is not GIC-400.
> X-Gene has gic-400 as an interrupt controller.
> Only thing is GIC pages are mapped at 64K boundary (with 64K page size)
> Hence CPU, VCPU interfaces has a size of 128K (2GIC pages)
> Regarding GICC_DIR, yes there is a problem which needs to be solved
> since the first page size is 64K.
> In XEN we already have a small fix to access GICC_DIR with 64K page
> offset instead of standard 4K.
> I remember a small discussion in this regard in past
> (http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/266468.html)
> which was deferred at that time.
> Once this patch is accepted we can post RFC patch to address GICC_DIR
> and discuss further.

I've had a look at my X-Gene board, and noticed the following thing:

Mustang# md.l 0x78020000 0x10
78020000: 000001e7 00000080 00000002 000003ff    ................
78020010: 00000000 000000ff 000003ff 00000003    ................
78020020: 000003ff 00000000 000003ff 00000000    ................
78020030: 00000000 00000000 00000000 00000000    ................
Mustang# md.l 0x7802f000 0x10
7802f000: 000001e7 00000080 00000002 000003ff    ................
7802f010: 00000000 000000ff 000003ff 00000003    ................
7802f020: 000003ff 00000000 000003ff 00000000    ................
7802f030: 00000000 00000000 00000000 00000000    ................

Notice a pattern? Yes, X-Gene is aliasing the GICC region over the 64k
page, repeated 16 times, as it should.

So either the DT is fixed to show GICC and GICV at offset 0xf000 (and we
don't support 64k pages with it), or we extend the binding to present an
offset inside the 128K region.

My preference goes of course to the latter, because for once we seem to
have something designed as expected.

Rob, what do you think?

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

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