Re: [PATCH] dt-bindings: spi: xilinx: Add clocks & clock-names properties

[Krzysztof Kozlowski <krzk@kernel.org>]

On 03/10/2024 09:42, Mahapatra, Amit Kumar wrote:
> Hello Krzysztof,
> 
>> -----Original Message-----
>> From: Krzysztof Kozlowski <krzk@kernel.org>
>> Sent: Thursday, October 3, 2024 12:31 PM
>> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra@amd.com>; Conor Dooley
>> <conor@kernel.org>
>> Cc: broonie@kernel.org; robh@kernel.org; krzk+dt@kernel.org;
>> conor+dt@kernel.org; Simek, Michal <michal.simek@amd.com>; linux-
>> spi@vger.kernel.org; devicetree@vger.kernel.org; linux-arm-
>> kernel@lists.infradead.org; linux-kernel@vger.kernel.org; git (AMD-Xilinx)
>> <git@amd.com>; amitrkcian2002@gmail.com
>> Subject: Re: [PATCH] dt-bindings: spi: xilinx: Add clocks & clock-names properties
>>
>> On 03/10/2024 08:23, Mahapatra, Amit Kumar wrote:
>>> Hello Conor,
>>>
>>>> -----Original Message-----
>>>> From: Conor Dooley <conor@kernel.org>
>>>> Sent: Monday, September 30, 2024 10:10 PM
>>>> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra@amd.com>
>>>> Cc: Krzysztof Kozlowski <krzk@kernel.org>; broonie@kernel.org;
>>>> robh@kernel.org;
>>>> krzk+dt@kernel.org; conor+dt@kernel.org; Simek, Michal
>>>> <michal.simek@amd.com>; linux-spi@vger.kernel.org;
>>>> devicetree@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
>>>> linux-kernel@vger.kernel.org; git (AMD-Xilinx) <git@amd.com>;
>>>> amitrkcian2002@gmail.com
>>>> Subject: Re: [PATCH] dt-bindings: spi: xilinx: Add clocks &
>>>> clock-names properties
>>>>
>>>> On Mon, Sep 30, 2024 at 03:44:47PM +0000, Mahapatra, Amit Kumar wrote:
>>>>> Hello Conor,
>>>>>
>>>>>>>>>>> Subject: Re: [PATCH] dt-bindings: spi: xilinx: Add clocks &
>>>>>>>>>>> clock-names properties
>>>>>>>>>>>
>>>>>>>>>>> On Mon, Sep 23, 2024 at 06:02:42PM +0530, Amit Kumar Mahapatra
>>>> wrote:
>>>>>>>>>>>> Include the 'clocks' and 'clock-names' properties in the AXI
>>>>>>>>>>>> Quad-SPI bindings. When the AXI4-Lite interface is enabled,
>>>>>>>>>>>> the core operates in legacy mode, maintaining backward
>>>>>>>>>>>> compatibility with version 1.00, and uses 's_axi_aclk' and
>>>>>>>>>>>> 'ext_spi_clk'. For the AXI interface, it uses 's_axi4_aclk'
>>>>>>>>>>>> and
>>>> 'ext_spi_clk'.
>>>>>>
>>>>>>>>>>>> +      properties:
>>>>>>>>>>>> +        clock-names:
>>>>>>>>>>>> +          items:
>>>>>>>>>>>> +            - const: s_axi_aclk
>>>>>>>>>>>> +            - const: ext_spi_clk
>>>>>>>>>>>
>>>>>>>>>>> These are all clocks, there should be no need to have "clk" in the
>> names.
>>>>>>>>>>
>>>>>>>>>> These are the names exported by the IP and used by the DTG.
>>>>>>>>>
>>>>>>>>> So? This is a binding, not a verilog file.
>>>>>>>>
>>>>>>>> Axi Quad SPI is an FPGA-based IP, and the clock names are derived
>>>>>>>> from the IP signal names as specified in the IP documentation [1].
>>>>>>>> We chose these names to ensure alignment with the I/O signal
>>>>>>>> names listed in Table 2-2 on page 19 of [1].
>>>>>>>>
>>>>>>>> [1]
>>>>>>>> chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.amd.
>>>>>>>> com/content/dam/xilinx/support/documents/ip_documentation/axi_qu
>>>>>>>> ad_s
>>>>>>>> pi/v3_2/pg153-axi-quad-spi.pdf
>>>>>>>
>>>>>>> So if hardware engineers call them "pink_pony_clk_aclk_really_clk"
>>>>>>> we should follow...
>>>>>>>
>>>>>>>  - bus or axi
>>>>>>>  - ext_spi or spi
>>>>>>>
>>>>>>> You have descriptions of each item to reference real signals.
>>>>>>> Conor's comment is valid - do no make it verilog file.
>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>> +
>>>>>>>>>>>> +    else:
>>>>>>>>>>>> +      properties:
>>>>>>>>>>>> +        clock-names:
>>>>>>>>>>>> +          items:
>>>>>>>>>>>> +            - const: s_axi4_aclk
>>>>>>>>>>>> +            - const: ext_spi_clk
>>>>>>>
>>>>>>> Nah, these are the same.
>>>>>>
>>>>>> They may be different, depending on whether or not the driver has
>>>>>> to handle "axi4- lite" versus "axi" differently. That said, I find
>>>>>> the commit message kinda odd in that it states that axi4-lite goes
>>>>>> with the s_axi_aclk
>>>> clock and axi goes with s_axi4_aclk.
>>>>>
>>>>> Apologies for the typo. When the AXI4 interface is enabled, it uses
>>>>> s_axi4_aclk, and when the AXI4-Lite interface is enabled, it uses s_axi_aclk.
>>>>>
>>>>> In my next series I will update my commit message & change the
>>>>> clock-names 's_axi4_aclk', 's_axi_aclk' & 'ext_spi_clk' to 'axi4',
>>>>> 'axi' & 'ref' respectively
>>>>
>>>> There's no driver here, so it is hard to know (why isn't there?) -
>>>> are you using the axi
>>>
>>> We are working on the driver. Once it is ready we will send it to upstream.
>>
>> Why would you send separate binding from driver? That's only making everything
>> more difficult...
> 
> Alright, I will send the next version along with the driver changes.
> 
>>
>>>
>>>> v axi4 to do some sort of differentiation in the driver?
>>> In the driver we don't do any different operations based on the clocks
>>> , we simply enable the available clocks in the driver.
>>
>> So it is the same clock?
> 
> These are two different clocks and depending on the mode—Legacy or 
> Enhanced—either clock will be enabled, but the purpose of both the 
> clocks are the same. We can have the name 'axi' for both the 
> clocks (axi & axi4). Please let me know if you are fine with this.

Please read my first comment in this thread. We are dragging this way
too much...

Best regards,
Krzysztof