linux-kernel - Re: [PATCH v2 1/3] dt-bindings: misc: add bindings for Intel HPS Copy Engine

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Date:   Thu, 5 May 2022 10:18:57 -0700 (PDT)
From:   matthew.gerlach@...ux.intel.com
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
cc:     dinguyen@...nel.org, robh+dt@...nel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        krzysztof.kozlowski+dt@...aro.org
Subject: Re: [PATCH v2 1/3] dt-bindings: misc: add bindings for Intel HPS
 Copy Engine



On Thu, 5 May 2022, Krzysztof Kozlowski wrote:

> On 05/05/2022 00:41, matthew.gerlach@...ux.intel.com wrote:
>>> Please find appropriate directory matching this hardware, not "misc". As
>>> a fallback SoC related bindings end up in "soc".
>>
>> I thought misc seemed appropriate because it is a very specific IP block
>> in the FPGA connected to the HPS.  It does perform a simple DMA function;
>> so I considered putting it in the dma directory, but it also has some
>> hand-shaking registers between the HPS and a host processor connected to the
>> FPGA via PCIe; so I thought misc.  Since the HPS "soc" accesses the
>> component, I can put it in the "soc" directory, unless there is a better
>> suggestion.
>
> So let it be "soc".

I will move it to the soc directory.

>
>>>
>>> $ git grep address-cell
>>> Do not use inconsistent coding. The same applies to your DTS.
>>
>> Is the inconsistency the use of '0x' in the values of #address-cells and
>> #size-cells, or is the consistency having different values for
>> #address-cells and #size-cells or both?
>
> It's about "0x".

Got it.  I will remove the 0x.

>
>>
>>>
>>>> +        #size-cells = <0x1>;
>>>> +        ranges = <0x00000000 0x00000000 0xf9000000 0x00001000>;
>>>
>>> Why do you even need the simple-bus above and cannot put the device
>>> directly on the bus?
>>
>> On an Agilex chip, the HPS is connected to the FPGA via two bridges,
>> referred as the "HPS to FPGA bridge" and the "Lightweight HPS to FPGA
>> bridge".  An IP block in the FPGA could be connected to one or both of
>> these bridges.  I am anticipating device tree overlays being applied for
>> other IP blocks instantiated in the FPGA.
>
> OK
>
>>
>>>
>>>> +
>>>> +        hps_cp_eng@0 {
>>>
>>> No underscores in node names. Generic node name.
>>
>> I understand.  I am considering dma@0 for the generic node name.
>
> Let's keep the same as in DTS.

Yes, we want the example and the DTS to be the same.  It will be called 
dma-controller@0.

Thank you for the feedback,
Matthew

>
>
> Best regards,
> Krzysztof
>