RE: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED i2Cv2

[Ryan Chen <ryan_chen@aspeedtech.com>]

Hello Krzysztof,

> -----Original Message-----
> From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> Sent: Wednesday, February 22, 2023 4:26 PM
> To: Ryan Chen <ryan_chen@aspeedtech.com>; Rob Herring
> <robh+dt@kernel.org>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt@linaro.org>; Joel Stanley <joel@jms.id.au>; Andrew
> Jeffery <andrew@aj.id.au>; Philipp Zabel <p.zabel@pengutronix.de>;
> openbmc@lists.ozlabs.org; linux-arm-kernel@lists.infradead.org;
> linux-aspeed@lists.ozlabs.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED i2Cv2
> 
> On 22/02/2023 03:59, Ryan Chen wrote:
> > Hello Krzysztof,
> >
> >> -----Original Message-----
> >> From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> >> Sent: Tuesday, February 21, 2023 7:05 PM
> >> To: Ryan Chen <ryan_chen@aspeedtech.com>; Rob Herring
> >> <robh+dt@kernel.org>; Krzysztof Kozlowski
> >> <krzysztof.kozlowski+dt@linaro.org>; Joel Stanley <joel@jms.id.au>;
> >> Andrew Jeffery <andrew@aj.id.au>; Philipp Zabel
> >> <p.zabel@pengutronix.de>; openbmc@lists.ozlabs.org;
> >> linux-arm-kernel@lists.infradead.org;
> >> linux-aspeed@lists.ozlabs.org; linux-kernel@vger.kernel.org
> >> Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED
> >> i2Cv2
> >>
> >> On 21/02/2023 11:42, Ryan Chen wrote:
> >>>>>>> +    type: boolean
> >>>>>>> +    description: Enable i2c bus timeout for master/slave (35ms)
> >>>>>>
> >>>>>> Why this is property for DT? It's for sure not bool, but proper
> >>>>>> type coming from units.
> >>>>> This is i2c controller feature for enable slave mode inactive
> >>>>> timeout and also master mode sda/scl auto release timeout.
> >>>>> So I will modify to
> >>>>>   aspeed,timeout:
> >>>>> 	type: boolean
> >>>>>     description: I2C bus timeout enable for master/slave mode
> >>>>
> >>>> This does not answer my concerns. Why this is board specific?
> >>> Sorry, can’t catch your point.
> >>> It is not board specific. It is controller feature.
> >>> ASPEED SOC chip is server product, master connect may have
> >>> fingerprint connect to another board. And also support hotplug.
> >>> For example I2C controller as slave mode, and suddenly disconnected.
> >>> Slave state machine will keep waiting for master clock in for rx/tx transfer.
> >>> So it need timeout setting to enable timeout unlock controller state.
> >>> And in another side. As master mode, slave is clock stretching.
> >>> The master will be keep waiting, until slave release cll stretching.
> >>
> >> OK, thanks for describing the feature. I still do not see how this is DT
> related.
> >
> > Let me draw more about the board-specific.
> > The following is an example about i2c layout in board.
> > Board A
> 	Board B
> > --------------------------------------------------------
> 	--------------------------------------------------------
> > |    i2c bus#1(master/slave)  <--------------------> fingerprint.(can be unplug)
> <--------------------> i2c bus#x (master/slave) |
> > |    i2c bus#2(master) -> tmp i2c device     |
> 	|									|
> > |    i2c bus#3(master) -> adc i2c device      |					|
> 								|
> > --------------------------------------------------------
> 	--------------------------------------------------------
> > In this case i2c bus#1 need enable timeout, avoid suddenly unplug the
> connector. That slave will keep state to drive clock stretching.
> > So it is specific enable in i2c bus#1. Others is not needed enable timeout.
> > Does this draw is more clear in scenario?
> 
> I2C bus #1 works in slave mode? So you always need it for slave work?

Yes, it is both slave/master mode. It is always dual role. Slave must always work. 
Due to another board master will send.

> >
> >>>
> >>> So in those reason add this timeout design in controller.
> >>
> >> You need to justify why DT is correct place for this property. DT is
> >> not for configuring OS, but to describe hardware. I gave you one
> >> possibility
> >> - why different boards would like to set this property. You said it
> >> is not board specific, thus all boards will have it (or none of them).
> >> Without any other reason, this is not a DT property. Drop.
> >>
> >>>>
> >>>>>
> >>>>>>> +
> >>>>>>> +  byte-mode:
> >>>>>>> +    type: boolean
> >>>>>>> +    description: Force i2c driver use byte mode transmit
> >>>>>>
> >>>>>> Drop, not a DT property.
> >>>>>>
> >>>>>>> +
> >>>>>>> +  buff-mode:
> >>>>>>> +    type: boolean
> >>>>>>> +    description: Force i2c driver use buffer mode transmit
> >>>>>>
> >>>>>> Drop, not a DT property.
> >>>>>>
> >>>>> The controller support 3 different for transfer.
> >>>>> Byte mode: it means step by step to issue transfer.
> >>>>> Example i2c read, each step will issue interrupt then enable next step.
> >>>>> Sr (start read) | D | D | D | P
> >>>>> Buffer mode: it means, the data can prepare into buffer register,
> >>>>> then Trigger transfer. So Sr D D D P, only have only 1 interrupt handling.
> >>>>> The DMA mode most like with buffer mode, The differ is data
> >>>>> prepare in DRAM, than trigger transfer.
> >>>>>
> >>>>> So, should I modify to
> >>>>>   aspeed,byte:
> >>>>> 	type: boolean
> >>>>>     description: Enable i2c controller transfer with byte mode
> >>>>>
> >>>>>   aspeed,buff:
> >>>>> 	type: boolean
> >>>>>     description: Enable i2c controller transfer with buff mode
> >>>>
> >>>> 1. No, these are not bools but enum in such case.
> >>>
> >>> Thanks, will modify following.
> >>> aspeed,xfer_mode:
> >>>     enum: [0, 1, 2]
> >>>     description:
> >>>       0: byte mode, 1: buff_mode, 2: dma_mode
> >>
> >> Just keep it text - byte, buffered, dma
> >>
> >>>
> >>>> 2. And why exactly this is board-specific?
> >>>
> >>> No, it not depends on board design. It is only for register control
> >>> for
> >> controller transfer behave.
> >>> The controller support 3 different trigger mode for transfer.
> >>> Assign bus#1 ~ 3 : dma tranfer and assign bus#4 ~ 6 : buffer mode
> >>> transfer, That can reduce the dram usage.
> >>
> >> Then anyway it does not look like property for Devicetree. DT
> >> describes hardware, not OS behavior.
> >
> > The same draw, in this case, i2c bus#1 that is multi-master transfer
> architecture.
> > Both will inactive with trunk data. That cane enable i2c#1 use DMA transfer
> to reduce CPU utilized.
> > Others (bus#2/3) can keep byte/buff mode.
> 
> Isn't then current bus configuration for I2C#1 known to the driver?
> Jeremy asked few other questions around here...

No, The driver don't know currently board configuration.


Best regards,
Ryan