Re: [PATCH v5 3/5] arm64: dts: agilex: add dtsi for PCIe Root Port

[Krzysztof Kozlowski <krzk@kernel.org>]

On 02/02/2025 19:49, matthew.gerlach@linux.intel.com wrote:
> 
> 
> On Sun, 2 Feb 2025, Krzysztof Kozlowski wrote:
> 
>> On 01/02/2025 20:12, matthew.gerlach@linux.intel.com wrote:
>>>>
>>>>> they are also referenced in the following:
>>>>>      Documentation/devicetree/bindings/soc/intel/intel,hps-copy-engine.yaml
>>>>>      arch/arm64/boot/dts/intel/socfpga_agilex_n6000.dts
>>>>> I am not exactly sure where the right place is to define them, maybe
>>>>> Documentation/devicetree/bindings/arm/intel,socfpga.yaml. On the other
>>>>> hand, no code references these names; so it might make sense to just
>>>>> remove them.
>>>>
>>>> In general: nowhere, because simple bus does not have such properties.
>>>> It's not about reg-names only - you cannot have reg. You just did not
>>>> define here simple-bus.
>>>
>>> I understand. I will remove reg and reg-names.
>>
>> If you have there IO address space, then removal does not sound right,
>> either. You just need to come with the bindings for this dedicated
>> device, whatever this is. There is no description here, not much in
>> commit msg, so I don't know what is the device you are adding. PCI has
>> several bindings, so is this just host bridge?
> 
> The device associated with two address ranges may be best described as a 
> simple-bus. It is a bus between the CPU and the directly connected FPGA in 
> the same package as the SOC. The design programmed into the FPGA 
> determines the device(s) connected to the bus. The hardware implementing 

So it is part of FPGA?

> this bus does have reset lines which allow for safely reprogramming the 

Then it is not simple-bus. Simple-bus is our construct for simple
devices. You cannot have something a bit more complex and call it
simple-bus.

> FPGA while the SOC is running, which implies appropriate bindings as you 
> suggest. Something like the following might make sense:
> 
>  	aglx_hps_bridges: fpga-bus@80000000 {
>  		compatible = "altr,agilex-hps-fpga-bridge", "simple-bus";

FPGA bridge maybe, but not simple-bus. It does not look like a simple
bus if you have here some resources.

>  		reg = <0x80000000 0x20200000>,
>  		      <0xf9000000 0x00100000>;
>  		reg-names = "axi_h2f", "axi_h2f_lw";
>  		#address-cells = <0x2>;
>  		#size-cells = <0x1>;
>  		ranges = <0x00000000 0x00000000 0x80000000 0x00040000>,
>  			 <0x00000000 0x10000000 0x90100000 0x0ff00000>,
>  			 <0x00000000 0x20000000 0xa0000000 0x00200000>,
>  			 <0x00000001 0x00010000 0xf9010000 0x00008000>,
>  			 <0x00000001 0x00018000 0xf9018000 0x00000080>,
>  			 <0x00000001 0x00018080 0xf9018080 0x00000010>;
>  		reset = <&rst SOC2FPGA_RESET>, <&rst LWHPS2FPGA_RESET>;
Best regards,
Krzysztof