Re: [PATCH] arm64: dts: r8a7795: Increase the size of GIC-400 mapped registers

[Marc Zyngier <marc.zyngier@arm.com>]

On 10/05/16 14:33, Geert Uytterhoeven wrote:
> CC Marc, lakml
> 
> On Tue, Apr 19, 2016 at 8:29 AM, Dirk Behme <dirk.behme@de.bosch.com> wrote:
>> From: Pooya Keshavarzi <Pooya.Keshavarzi@de.bosch.com>
>>
>> There are some requirements about the GIC-400 memory layout and its
>> mapping if using 64k aligned base addresses like on r8a7795.
>>
>> See e.g.
>>
>> http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=21550029f709072aacf3b9
>>
>> Map the whole memory range instead of only 0x2000. This will fix
>> the issue that some hypervisors, e.g. Xen, fail to handle the
>> interrupts correctly.
>>
>> Signed-off-by: Pooya Keshavarzi <Pooya.Keshavarzi@de.bosch.com>
>> Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
> 
> Based on my understanding below
> Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
> 
>> ---
>> Note: This patch is against renesas-drivers-2016-04-12-v4.6-rc3
>>
>>  arch/arm64/boot/dts/renesas/r8a7795.dtsi | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/boot/dts/renesas/r8a7795.dtsi b/arch/arm64/boot/dts/renesas/r8a7795.dtsi
>> index 8be9424..d880fd4 100644
>> --- a/arch/arm64/boot/dts/renesas/r8a7795.dtsi
>> +++ b/arch/arm64/boot/dts/renesas/r8a7795.dtsi
>> @@ -160,9 +160,9 @@
>>                         #address-cells = <0>;
>>                         interrupt-controller;
>>                         reg = <0x0 0xf1010000 0 0x1000>,
>> -                             <0x0 0xf1020000 0 0x2000>,
>> +                             <0x0 0xf1020000 0 0x20000>,
>>                               <0x0 0xf1040000 0 0x20000>,
>> -                             <0x0 0xf1060000 0 0x2000>;
>> +                             <0x0 0xf1060000 0 0x20000>;
>>                         interrupts = <GIC_PPI 9
>>                                         (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_HIGH)>;
>>                 };
> 
> Region 0:
>     4 KiB-pages 0xf1011000-0xf101ffff are aliased to 0xf1010000-0xf1010fff,
>     but we need the first 4 KiB only.
> 
> Region 1:
>     4 KiB-pages 0xf1021000-0xf102ffff are aliased to 0xf1020000-0xf1020fff,
>     4 KiB-pages 0xf1030000-0xf103ffff are all zeroes, probably due to
>     non-secure mode?

No. This 4kB page only contain a single register (GICC_DIR), which is
WO/RAZ.

> 
> Region 2:
>     4 KiB-pages 0xf1041000-0xf104ffff are aliased to 0xf1040000-0xf1040fff,
>     4 KiB-pages 0xf1050000-0xf105ffff are all zeroes, probably due to
>     non-secure mode?

Neither. The aliases are an unused feature of GIC400 exposing the other
CPUs view of the same registers...

> 
> Region 3:
>     4 KiB-pages 0xf1061000-0xf106ffff are aliased to 0xf1060000-0xf1060fff,
>     4 KiB-pages 0xf1070000-0xf107ffff are all zeroes, probably due to
>     non-secure mode?

Same as region 1.

> 
> Region 2 already had a 128 KiB size before, which allowed to use 8 KiB at
> 0xf104f000.

No. This region (GICH) only needs the first 256 bytes or so. The rest is
either RAZ/WI or useless stuff.

> 
> An 8 KiB size for regions 1 and 3 indeed didn't make much sense, as this
> covered two identical (aliased) 4 KiB pages, instead of two different pages
> at offset 0xf000.

While we're at it, adding a pointer to the documentation (GIC400 and
SBSA) would be tremendously useful, as it'd avoid misinterpreting the
various bits.

Thanks,

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