Re: [PATCH v2 4/4] arm64: dts: broadcom: Add support for BCM2712

Florian Fainelli
2024-05-20T18:03:42Z

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On 5/16/24 01:36, Andrea della Porta wrote:
> On 09:14 Fri 10 May , Florian Fainelli wrote:
>> On 5/10/24 07:35, Andrea della Porta wrote:
>>
>> This should be #size-cells = <2> to be future proof and support over 4GB of
>> DRAM, because the DDR controller and the memory map on that chip have been
>> designed with that requirement.
>>
>>> +
>>> + interrupt-parent = <&gicv2>;
>>> +
>>> + axi: axi {
>>> + compatible = "simple-bus";
>>> + #address-cells = <2>;
>>> + #size-cells = <1>;
>>> + ranges;
>>
>> The AXI peripheral window should be defined in the ranges property. The
>> aperture is from 0x10_0000_0000 to 0x10_3FFF_FFFF.
>>
>> From that point on you can define all peripherals under the axi node to be
>> relative to that axi aperture, just like what you did for the legacy Pi
>> peripherals in the subsequent bus node.
>
> This doesn't seem to match with what I have here:
> - some axi peripherals goes beyond 0x10_3FFF_FFFF (e.g. the interrupt
> controller is @0x107fff9000)

The interrupt controller (GIC) is technically its own dedicated bus to
the CPU, that's why it is typically added to the root node.

> - downstream dts have that ranges going from 0x10 0x00000000 0x11 0x00000000,
> so to span all the peripheral (included e.g. the above int controller)
> - another comment in downstream dts says: // 10_00000000-1x_xxxxxxxx = up to
> 64GB system RAM

Yes, up to 64GB of DRAM is correct.

>
> I'm a little confused here, of course we could also define multiple ranges
> but I don't really know what the boundaries are. Anyway, I would opt for the
> extended range (0x10 0x00000000 - 0x11 0x00000000) unless there is concern
> about it. Any thoughts?

A single range is fine with me, those sort of details should not matter.

>
> Many thanks,
> Andrea
>
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--
Florian

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