Re: [PATCH 12/12] arm64: dts: exynos: Add Exynos850 SoC support

[Marc Zyngier <maz@kernel.org>]

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.

	M.

-- 
Without deviation from the norm, progress is not possible.