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Subject: Re: [PATCH 12/12] arm64: dts: exynos: Add Exynos850 SoC support
To:     Marc Zyngier <maz@kernel.org>
Cc:     Sam Protsenko <semen.protsenko@linaro.org>,
        Sylwester Nawrocki <s.nawrocki@samsung.com>,
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From:   Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Message-ID: <f9b233bb-628f-1a0f-468c-8a6c7d2b23a4@canonical.com>
Date:   Thu, 5 Aug 2021 09:35:12 +0200
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On 05/08/2021 09:30, Marc Zyngier wrote:
> On Thu, 05 Aug 2021 08:17:14 +0100,
> Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com> wrote:
>>
>> On 04/08/2021 23:30, Sam Protsenko wrote:
>>>>>
>>>>> Nice catch! Actually there is an error (typo?) in SoC's TRM, saying
>>>>> that Virtual Interface Control Register starts at 0x3000 offset (from
>>>>> 0x12a00000), where it obviously should be 0x4000, that's probably
>>>>> where this dts error originates from. Btw, I'm also seeing the same
>>>>> error in exynos7.dtsi.
>>>>
>>>> What's the error exactly? The "Virtual interface control register"
>>>> offset (3rd region) is set properly to 0x4000 on Exynos7. Also one for
>>>> the Exynos5433 looks correct.
>>>>
>>>
>>> The issue is that 2nd region's size is 0x1000, but it must be 0x2000.
>>> It's defined by GIC-400 architecture, as I understand. Please look at
>>> [1], table 3-1 has very specific offsets and sizes for each functional
>>> block, and each particular SoC must adhere to that spec. So having
>>> 0x1000 for 2nd region can't be correct. And because exynos7.dtsi has
>>> GIC-400 as well, and 0x1000 is specified there for 2nd region size
>>> too, so I presume there is the same mistake there.
>>
>> I understand, the range length has indeed same mistake. However it does
>> not matter that much There are no registers pass 0x10C (so pass 0x1000).
>> This address space is not used.
> 
> I have no idea which spec you are looking at, but the GICv2
> architecture (of which GIC400 is an implementation) definitely has a
> register in the second 4kB page of the CPU interface. It contains the
> GICC_DIR register, which is used to deactivate an interrupt when
> EOIMode==1.
> 
> Linux actively uses it when started at EL2.

I was checking Exynos TRM and it seems it has one more bug... The ARM
datasheet [1] indeed mentions GICC_DIR at 0x1000. I'll add "Fixes" tag
to my fix for Exynos7.

https://developer.arm.com/documentation/ddi0471/b/programmers-model/cpu-interface-register-summary


Best regards,
Krzysztof