Re: [PATCH v4 2/3] dt-bindings: fpga: xlnx,fpga-selectmap: add DT schema

[Charles Perry <charles.perry@savoirfairelinux.com>]

On Feb 27, 2024, at 3:10 AM, Krzysztof Kozlowski krzysztof.kozlowski@linaro.org wrote:

> On 21/02/2024 20:50, Charles Perry wrote:
>> Document the SelectMAP interface of Xilinx 7 series FPGA.
>> 
>> Signed-off-by: Charles Perry <charles.perry@savoirfairelinux.com>
>> ---
>>  .../bindings/fpga/xlnx,fpga-selectmap.yaml    | 86 +++++++++++++++++++
>>  1 file changed, 86 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..08a5e92781657
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/fpga/xlnx,fpga-selectmap.yaml
>> @@ -0,0 +1,86 @@
>> +# 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@savoirfairelinux.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-xc7s-selectmap
>> +      - xlnx,fpga-xc7a-selectmap
>> +      - xlnx,fpga-xc7k-selectmap
>> +      - xlnx,fpga-xc7v-selectmap
>> +
>> +  reg:
>> +    description:
>> +      At least 1 byte of memory mapped IO
>> +    maxItems: 1
>> +
>> +  prog_b-gpios:
> 
> I commented on this and still see underscore. Nothing in commit msg
> explains why this should have underscore. Changelog is also vague -
> describes that you brought back underscores, instead of explaining why
> you did it.
> 
> So the same comments as usual:
> 
> No underscores in names.
> 
> Best regards,
> Krzysztof

Hello Krzysztof,

Yes, I've gone full circle on that issue. Here's what I tried so far:

 1) Reuse the same gpio names: Duplicates errors of the past, Krzysztof
    doesn't like it.
 2) Different gpio names for new driver only: Makes the driver code
    overly complicated, Yilun doesn't like it.
 3) Change gpio names for both drivers, deprecate the old names: Makes
    the DT binding and the driver code overly complicated, Rob doesn't
    like it.

I think that while the driver code shouldn't be the driving force for
the DT spec, it can be a good indication that the spec is unpractical to
implement.

In this case, there are two interfaces on a chip that uses the same GPIO
protocol, it would only make sense that they use the same names, this
discards solution #2.

That leaves us with #1 or #3, which is to ask if the added complexity to
the driver code and DT binding is worth it for a gain in naming
convention.

There might also be another solution that I haven't seen.

Regards,
Charles