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

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Message-ID: <20240930-unbalance-wake-e1a6f07ea79d@spud>
Date: Mon, 30 Sep 2024 17:40:15 +0100
From: Conor Dooley <conor@...nel.org>
To: "Mahapatra, Amit Kumar" <amit.kumar-mahapatra@....com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"robh@...nel.org" <robh@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	"Simek, Michal" <michal.simek@....com>,
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"git (AMD-Xilinx)" <git@....com>,
	"amitrkcian2002@...il.com" <amitrkcian2002@...il.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_quad_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 v axi4 to do some sort of differentiation in the driver?

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