linux-kernel - Re: [PATCH 2/3] dt-bindings: fpga: xlnx,fpga-slave-selectmap: add DT schema

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Date: Fri, 2 Feb 2024 11:49:45 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Charles Perry <charles.perry@...oirfairelinux.com>
Cc: mdf <mdf@...nel.org>, Allen VANDIVER <avandiver@...kem-imaje.com>,
 Brian CODY <bcody@...kem-imaje.com>, hao wu <hao.wu@...el.com>,
 yilun xu <yilun.xu@...el.com>, Tom Rix <trix@...hat.com>,
 Rob Herring <robh+dt@...nel.org>,
 krzysztof kozlowski+dt <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Michal Simek <michal.simek@....com>,
 linux-fpga <linux-fpga@...r.kernel.org>,
 devicetree <devicetree@...r.kernel.org>,
 linux-kernel <linux-kernel@...r.kernel.org>,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/3] dt-bindings: fpga: xlnx,fpga-slave-selectmap: add DT
 schema

On 01/02/2024 19:24, Charles Perry wrote:
> 
> 
> ----- On Feb 1, 2024, at 3:07 AM, Krzysztof Kozlowski krzysztof.kozlowski@...aro.org wrote:
> 
>> On 01/02/2024 00:05, Charles Perry wrote:
>>> Document the slave SelectMAP interface of Xilinx 7 series FPGA.
>>>
>>> Signed-off-by: Charles Perry <charles.perry@...oirfairelinux.com>
>>> ---
>>>  .../bindings/fpga/xlnx,fpga-selectmap.yaml    | 83 +++++++++++++++++++
>>>  1 file changed, 83 insertions(+)
>>>  create mode 100644
>>>  Documentation/devicetree/bindings/fpga/xlnx,fpga-selectmap.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/fpga/xlnx,fpga-selectmap.yaml
>>> b/Documentation/devicetree/bindings/fpga/xlnx,fpga-selectmap.yaml
>>> new file mode 100644
>>> index 0000000000000..c9a446b43cdd9
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/fpga/xlnx,fpga-selectmap.yaml
>>> @@ -0,0 +1,83 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/fpga/xlnx,fpga-selectmap.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: Xilinx SelectMAP FPGA interface
>>> +
>>> +maintainers:
>>> +  - Charles Perry <charles.perry@...oirfairelinux.com>
>>> +
>>> +description: |
>>> +  Xilinx 7 Series FPGAs support a method of loading the bitstream over a
>>> +  parallel port named the SelectMAP interface in the documentation. Only
>>> +  the x8 mode is supported where data is loaded at one byte per rising edge of
>>> +  the clock, with the MSB of each byte presented to the D0 pin.
>>> +
>>> +  Datasheets:
>>> +
>>> https://www.xilinx.com/support/documentation/user_guides/ug470_7Series_Config.pdf
>>> +
>>> +allOf:
>>> +  - $ref: /schemas/memory-controllers/mc-peripheral-props.yaml#
>>> +
>>> +properties:
>>> +  compatible:
>>> +    enum:
>>> +      - xlnx,fpga-selectmap
>>
>> Your description mentions "7 Series" which is not present in compatible
>> and title. What is exactly the product here? Interface usually is not
>> the final binding, so is this specific to some particular FPGA or SoC?
>>
>>
>> Best regards,
>> Krzysztof
> 
> This is specific to the FPGA, the 7 series encompass the following part
> family:
>  * Spartan-7 (XC7S6, XC7S15, ... XC7S100)
>  * Artix-7 (XC7A12T, XC7A15T, ... XC7A200T)
>  * Kintex-7 (XC7K70T, XC7K160T, ... XC7K480T)
>  * Virtex-7 (XC7V585T, XC7V2000T, 
>              XC7VX330T, XC7VX415T, ... XC7VX1140T,
>              XC7VH580T, XC7VH870T)
> 
> 
> The configuration guide of Xilinx [1] tells us that all those devices
> share a common programming scheme.
> 
> I do agree that having a mention of "7 series" in the compatible name
> would be beneficial as Xilinx has more FPGA than just the 7 series.
> The name was inspired from "xlnx,fpga-slave-serial" which is the compatible
> for the serial interface.
> 
> What about "xlnx,fpga-xc7-selectmap" ?
> 

I am not sure what xc7 is and how Xilinx numbers it products, but
compatibles are supposed to be device specific, not family. Common
programming model could be denoted with generic fallback, but then the
fallback could be device-specific as well, which usually we recommend.

Best regards,
Krzysztof