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Date: Fri, 19 Jan 2024 12:13:22 -0500
From: Frank Li <Frank.li@nxp.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc: Conor Dooley <conor@kernel.org>,
	Conor Dooley <conor.dooley@microchip.com>, robh@kernel.org,
	alexandre.belloni@bootlin.com, conor.culhane@silvaco.com,
	gregkh@linuxfoundation.org, imx@lists.linux.dev,
	jirislaby@kernel.org, joe@perches.com,
	linux-i3c@lists.infradead.org, linux-kernel@vger.kernel.org,
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	zbigniew.lukwinski@linux.intel.com, devicetree@vger.kernel.org,
	krzysztof.kozlowski+dt@linaro.org
Subject: Re: [PATCH v2 2/7] dt-bindings: i3c: svc: add compatible string i3c:
 silvaco,i3c-target-v1
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On Wed, Jan 17, 2024 at 01:06:15PM -0500, Frank Li wrote:
> On Wed, Jan 17, 2024 at 06:15:51PM +0100, Krzysztof Kozlowski wrote:
> > On 17/01/2024 17:19, Frank Li wrote:
> > >>
> > >> Not really, because compatible describes hardware and it is the same
> > >> hardware here. We do not have two different compatibles for GPIOs being
> > >> input or output.  Or two different compatibles for serial engines (ones
> > >> providing UART, SPI or I2C).
> > > 
> > > GPIO and UART is simple. Actuall SPI and I2C have two mode, slave and
> > 
> > I talked about serial engines which can be multiple: UART, SPI and I2C.
> > 
> > > master. Many SPI/I2C is dual mode controller. Just seldom use slave mode
> > > at linux side. So you just see master mode SPI/I2C controller in dt-binding
> > > and dts file. So few people upstream slave part to linux kernel community.
> > > They have the exact same problems if support slave mode.
> > > 
> > > PCI is typical example: 
> > > EP mode:  Documentation/devicetree/bindings/pci/qcom,pcie-ep.yaml
> > > RC mode:  Documentation/devicetree/bindings/pci/qcom,pcie.yaml
> > > 
> > > Which is the same hardware for two difference compatible string.
> > 
> > That's the only case, I recall.
> 
> As my knowledge, yes. 
> 
> > 
> > >>
> > >>>
> > >>> I can write git commit message like:
> > >>>
> > >>> dt-bindings: i3c: svc: add compatible string nxp,imx93-svc-i3c-target
> > >>>
> > >>> silvaco i3c controller is dual mode controller, which can work as master
> > >>> and target mode. All clock, reg, irq are the same for both mode. Add
> > >>> compatible string "nxp,imx93-svc-i3c-target" to let silivaco i3c
> > >>> controller work as target mode.
> > >>>
> > >>> Of course, alternate method to added a property "mode" to distingiush
> > >>> master and target mode. but old "silvaco,i3c-master-v1" will actually work
> > >>> as dual mode support. Driver structure will become complex.
> > >>
> > >> Please send full DTS of user for this, which works for 100%, so we can
> > >> see how it differs from controller mode. If your code snippet from other
> > >> thread is correct, then it would suggest "mode" property or lack of
> > >> children. Maybe lack of children is not enough, if user-space could
> > >> control I3C bus.
> > > 
> > > According to current implment, only need change imx93.dtsi's @i3c1's 
> > > compatible string to "silvaco,i3c-target-v1". I attached imx93 dts node for
> > > your reference.
> > > 
> > > 	i3c1: i3c-master@44330000 {                        
> > >                                 compatible = "silvaco,i3c-master-v1"; 
> > > 					     ^^^^ only need change here!
> > 
> > Nope, don't change compatibles of existing nodes. Unreadable and
> > unmanageable code.
> 
> It is just show minimize difference.
> 
> Normally, it should be.
> 
> 	i3c1: i3c-master@44330000 {
> 		...
> 		compatible = "silvaco,i3c-master-v1";
> 		...
> 		status = disabled;
> 	}
> 	
> 	i3c1-target: i3c-target@44330000 {
> 		...
> 		compatible = "silvaco,i3c-target-v1";
> 		...
> 		status = disabled;
> 	}
> 
> in board dts
> 
> @i3c1{
> 	status = "okay";
> }
> 
> Or
> @i3c1-target{
> 	status = "okay";
> }
> > 
> > >    
> > >                                 reg = <0x44330000 0x10000>;                
> > >                                 interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
> > >                                 #address-cells = <3>;                      
> > >                                 #size-cells = <0>;                         
> > >                                 clocks = <&clk IMX93_CLK_BUS_AON>,         
> > >                                          <&clk IMX93_CLK_I3C1_GATE>,       
> > >                                          <&clk IMX93_CLK_I3C1_SLOW>;       
> > >                                 clock-names = "pclk", "fast_clk", "slow_clk";
> > >                                 dmas = <&edma1 6 0 1>, <&edma1 5 0 0>;     
> > >                                 dma-names = "rx", "tx";                    
> > >                                 status = "disabled";                       
> > >                         }; 
> > 
> > That's not a patch for existing file. I did not claim you cannot write
> > such DTS. I claimed you don't have such DTS for upstream...
> 
> Yes, it need finialize this topic before handle dts upstream.
> 
> > 
> > > 
> > > For master mode:
> > > Unlike i2c. Genenally I3C can auto probe children node like USB can auto
> > > detect attached devices. So I3C master can work without children nodes.
> > > Such as auto load i3c sensor driver according to i3c standard vendor id and
> > > production id.
> > 
> > Then presence of children cannot be used.
> > 
> > > 
> > > For target mode: using configfs to controller I3C.
> > > 
> > > mkdir /sys/kernel/config/i3c_target/functions/tty/t
> > > echo 0x011b > /sys/kernel/config/i3c_target/functions/tty/t/vendor_id
> > > echo 0x1000 > /sys/kernel/config/i3c_target/functions/tty/t/part_id
> > > echo 0x6 > /sys/kernel/config/i3c_target/functions/tty/t/bcr
> > > 
> > > ln -s /sys/kernel/config/i3c_target/functions/tty/t /sys/kernel/config/i3c_target/controllers/44330000.i3c-master/
> > > 
> > > Then you echo test >/dev/ttySI3C0.
> > > 
> > > Unlike USB, user can switch host and gadget mode dymatically. Suppose I3C
> > > only work on one of master or slave mode only, which is static.
> > 
> > I don't understand this. So it can switch dynamically or not?
> 
> I3C Protocal allow do that. But no one really do that. 
> 
> > 
> > > 
> > > Although it is one hardware, I think it is exculsive multi function device.
> > 
> > Just like serial engines. Do you see there replacing compatibles? No.
> > 
> > > 
> > > Summary: basice two option to distingiush controller and target mode.
> > > 1. by "compatible" string
> > > 2. by "mode"
> > > 
> > > I think 1 is relatively simple and easy to understand.
> > 
> > Eh, if you only saw my comments on people replacing compatibles...
> > Anyway, I stated my reasons, so to reiterate: NAK.
> 
> I know it.  Needn't emphase it every time.
> 
> Is using "mode" ('controller' and 'target') proptery okay?

@krzyszkof:
	Do you agree using "mode"?

Frank
> 
> Frank
> 
> > 
> > Best regards,
> > Krzysztof
> >