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

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Date: Tue, 30 Jan 2024 10:45:44 -0500 (EST)
From: Charles Perry <charles.perry@...oirfairelinux.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: mdf@...nel.org, hao wu <hao.wu@...el.com>, yilun xu <yilun.xu@...el.com>, 
	trix@...hat.com, 
	krzysztof kozlowski+dt <krzysztof.kozlowski+dt@...aro.org>, 
	Brian CODY <bcody@...kem-imaje.com>, 
	Allen VANDIVER <avandiver@...kem-imaje.com>, 
	linux-fpga@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: fpga: xlnx,fpga-slave-selectmap: add
 DT schema

----- On Jan 30, 2024, at 2:52 AM, Krzysztof Kozlowski krzysztof.kozlowski@...aro.org wrote:

> On 29/01/2024 23:56, Charles Perry wrote:
>> Document the slave SelectMAP interface of Xilinx 7 series FPGA.
>> 
>> Signed-off-by: Charles Perry <charles.perry@...oirfairelinux.com>
>> ---
>>  .../fpga/xlnx,fpga-slave-selectmap.yaml       | 85 +++++++++++++++++++
>>  1 file changed, 85 insertions(+)
>>  create mode 100644
>>  Documentation/devicetree/bindings/fpga/xlnx,fpga-slave-selectmap.yaml
>> 
>> diff --git
>> a/Documentation/devicetree/bindings/fpga/xlnx,fpga-slave-selectmap.yaml
>> b/Documentation/devicetree/bindings/fpga/xlnx,fpga-slave-selectmap.yaml
>> new file mode 100644
>> index 0000000000000..20cea24e3e39a
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/fpga/xlnx,fpga-slave-selectmap.yaml
>> @@ -0,0 +1,85 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/fpga/xlnx,fpga-slave-selectmap.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Xilinx Slave SelectMAP FPGA
>> +
>> +description: |
>> +  Xilinx 7 Series FPGAs support a method of loading the bitstream over a
>> +  parallel port named the slave 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
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - xlnx,fpga-slave-selectmap
> 
> You did not test bindings, so only limited review.
> 

I had issues installing pylibfdt but that's fixed now, will do.

>> +
>> +  reg:
>> +    description:
>> +      At least 1 byte of memory mapped IO
>> +    maxItems: 1
>> +
>> +  prog_b-gpios:
> 
> 
> No underscores in names.
> 

This is heavily based on "xlnx,fpga-slave-serial.yaml" which uses an underscore.
I can use a dash instead but that would make things inconsistent across the two schemas. 

> 
>> +    description:
>> +      config pin (referred to as PROGRAM_B in the manual)
>> +    maxItems: 1
>> +
>> +  done-gpios:
>> +    description:
>> +      config status pin (referred to as DONE in the manual)
>> +    maxItems: 1
>> +
>> +  init-b-gpios:
> 
> Is there init-a? Open other bindings and look how these are called there.
> 

No, the "-b" is there to denote that the signal is active low. I think its shorthand
for "bar" which is the overline (‾) that electronic engineer put on top of the name of the
signal on schematics. It comes from the datasheet.

> 
>> +    description:
>> +      initialization status and configuration error pin
>> +      (referred to as INIT_B in the manual)
>> +    maxItems: 1
>> +
>> +  csi-b-gpios:
> 
> Where is csi-a?
> 

No "csi-a", this is the CSI signal which is active low.

>> +    description:
>> +      chip select pin (referred to as CSI_B in the manual)
>> +      Optional gpio for if the bus controller does not provide a chip select.
>> +    maxItems: 1
>> +
>> +  rdwr-b-gpios:
>> +    description:
>> +      read/write select pin (referred to as RDWR_B in the manual)
>> +      Optional gpio for if the bus controller does not provide this pin.
>> +    maxItems: 1
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - prog_b-gpios
>> +  - done-gpios
>> +  - init-b-gpios
>> +
>> +additionalProperties: true
> 
> Nope, this cannot bue true.
> 

Ok, I'll put this to false but I'm not quite sure I understand the implications.

My reasoning behind assigning this to true was that the FPGA is an external
device on a bus that needs to be configured by a bus controller. The bus controller
would be the parent of the fpga DT node and the later would contain properties
parsed by the bus controller driver.

>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/gpio/gpio.h>
>> +    &weim {
> 
> Drop or use some generic soc
> 

Ok

>> +      status = "okay";
> 
> Drop
> 

Ok

>> +      ranges = <0 0 0x08000000 0x04000000>;
> 
> Drop
> 

Ok

>> +
>> +      fpga_mgr: fpga_programmer@0,0 {
> 
> No underscores in names, drop label.
> 
> Node names should be generic. See also an explanation and list of
> examples (not exhaustive) in DT specification:
> https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#generic-names-recommendation
> 
> 

Ok, will use "fpga-mgr" as this seems to be the most common one for fpga managers.

>> +        compatible = "xlnx,fpga-slave-selectmap";
>> +        reg = <0 0 0x4000000>;
>> +        fsl,weim-cs-timing = <0x00070031 0x00000142
>> +              0x00020000 0x00000000
>> +              0x0c000645 0x00000000>;
> 
> NAK.
> 
> Please run your patch through Xilinx folks before sending.
> 
> Best regards,
> Krzysztof

Thank you,
Charles