RE: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for AST2600-i2cv2

Ryan Chen
2023-03-03T08:30:29Z

Hello Krzysztof,

> -----Original Message-----
> From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> Sent: Friday, March 3, 2023 4:20 PM
> To: Ryan Chen <ryan_chen@aspeedtech.com>; Wolfram Sang
> <wsa@kernel.org>
> Cc: Joel Stanley <joel@jms.id.au>; Brendan Higgins
> <brendan.higgins@linux.dev>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt@linaro.org>; Andrew Jeffery <andrew@aj.id.au>;
> devicetree@vger.kernel.org; Philipp Zabel <p.zabel@pengutronix.de>; Rob
> Herring <robh+dt@kernel.org>; Benjamin Herrenschmidt
> <benh@kernel.crashing.org>; linux-aspeed@lists.ozlabs.org;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> openbmc@lists.ozlabs.org; linux-i2c@vger.kernel.org
> Subject: Re: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for AST2600-i2cv2
>
> On 01/03/2023 06:57, Ryan Chen wrote:
> > Hello Krzysztof,
> >
> >> -----Original Message-----
> >> From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> >> Sent: Monday, February 27, 2023 4:25 PM
> >> To: Ryan Chen <ryan_chen@aspeedtech.com>; Andrew Jeffery
> >> <andrew@aj.id.au>; Brendan Higgins <brendan.higgins@linux.dev>;
> >> Benjamin Herrenschmidt <benh@kernel.crashing.org>; Joel Stanley
> >> <joel@jms.id.au>; Rob Herring <robh+dt@kernel.org>; Krzysztof
> >> Kozlowski <krzysztof.kozlowski+dt@linaro.org>; Philipp Zabel
> >> <p.zabel@pengutronix.de>; linux-i2c@vger.kernel.org;
> >> openbmc@lists.ozlabs.org; devicetree@vger.kernel.org;
> >> linux-arm-kernel@lists.infradead.org;
> >> linux-aspeed@lists.ozlabs.org; linux-kernel@vger.kernel.org
> >> Subject: Re: [PATCH v6 1/2] dt-bindings: i2c: aspeed: support for
> >> AST2600-i2cv2
> >>
> >> On 26/02/2023 04:13, Ryan Chen wrote:
> >>> Add ast2600-i2cv2 compatible and aspeed,global-regs, aspeed,timeout
> >>> aspeed,xfer-mode description for ast2600-i2cv2.
> >>>
> >>> Signed-off-by: Ryan Chen <ryan_chen@aspeedtech.com>
> >>> ---
> >>> .../devicetree/bindings/i2c/aspeed,i2c.yaml | 44
> +++++++++++++++++++
> >>> 1 file changed, 44 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>> b/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>> index f597f73ccd87..75de3ce41cf5 100644
> >>> --- a/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>> +++ b/Documentation/devicetree/bindings/i2c/aspeed,i2c.yaml
> >>> @@ -49,6 +49,25 @@ properties:
> >>> description:
> >>> states that there is another master active on this bus
> >>>
> >>> + aspeed,timeout:
> >>> + type: boolean
> >>> + description: I2C bus timeout enable for master/slave mode
> >>
> >> Nothing improved here in regards to my last comment.
> >
> > Yes, as I know your require is about " DT binding to represent hardware
> setup"
> > So I add more description about aspeed,timeout as blow.
> >
> > ASPEED SOC chip is server product, i2c bus may have fingerprint connect to
> another board. And also support hotplug.
> > The following is board-specific design example.
> > Board A Board B
> > ------------------------- ------------------------
> > |i2c bus#1(master/slave) <===fingerprint ===> i2c bus#x (master/slave)|
> > |i2c bus#2(master)-> tmp i2c device | |
> |
> > |i2c bus#3(master)-> adc i2c device | |
> |
> > ------------------------- ------------------------
> >
> > aspeed,timout properites:
> > For example I2C controller as slave mode, and suddenly disconnected.
> > Slave state machine will keep waiting for master clock in for rx/tx transmit.
> > So it need timeout setting to enable timeout unlock controller state.
> > And in another side. In Master side also need avoid suddenly slave
> miss(un-plug), Master will timeout and release the SDA/SCL.
> >
> > Do you mean add those description into ore aspeed,timout properites
> description?
>
> You are describing here one particular feature you want to enable in the driver
> which looks non-scalable and more difficult to configure/use.
> What I was looking for is to describe the actual configuration you have (e.g.
> multi-master) which leads to enable or disable such feature in your hardware.
> Especially that bool value does not scale later to actual timeout values in time
> (ms)...
>
> I don't know I2C that much, but I wonder - why this should be specific to
> Aspeed I2C and no other I2C controllers implement it? IOW, this looks quite
> generic and every I2C controller should have it. Adding it specific to Aspeed
> suggests that either we miss a generic property or this should not be in DT at
> all (because no one else has it...).
>
> Also I wonder, why you wouldn't enable timeout always...
>
> +Cc Wolfram,
> Maybe you know whether bool "timeout" property for one controller makes
> sense? Why we do not have it for all controllers?
>
Because, i2c bus didn’t specific timeout.
But SMBus defines a clock low time-out, TIMEOUT of 35 ms.

It have definition in SMBus specification.
http://smbus.org/specs/SMBus_3_1_20180319.pdf
You can check Page 18, Note3 that have timeout description.

> >>
> >>> +
> >>> + aspeed,xfer-mode:
> >>> + description: |
> >>> + I2C bus transfer mode selection.
> >>> + - "byte": I2C bus byte transfer mode.
> >>> + - "buffered": I2C bus buffer register transfer mode.
> >>> + - "dma": I2C bus dma transfer mode (default)
> >>> + items:
> >>> + enum: [byte, buffered, dma]
> >>> + maxItems: 1
> >>
> >> Drop, not an array.
> >>
> >>> + $ref: /schemas/types.yaml#/definitions/non-unique-string-array
> >>
> >> Wrong ref. This is not an array, but one string.
> >
> > Sorry, I can't catch your "one string" point.
>
> How many strings you are going to have in this property? If one
> (maxItems: 1), then this is not an array.
>
> > Could you point me what ref I can refer to?
> > That I can check into Linux example. Thanks a lot.
> >>
> >>> +
> >>> + aspeed,global-regs:
> >>> + $ref: /schemas/types.yaml#/definitions/phandle
> >>> + description: The phandle of i2c global register node.
> >>> +
> >>> required:
> >>> - reg
> >>> - compatible
> >>> @@ -57,6 +76,19 @@ required:
> >>>
> >>> unevaluatedProperties: false
> >>>
> >>> +if:
> >>
> >> This should be under allOf (in this location)
> >>
> >>> + properties:
> >>> + compatible:
> >>> + contains:
> >>> + const: aspeed,ast2600-i2cv2
> >>> +
> >>> +then:
> >>> + properties:
> >>> + reg:
> >>> + minItems: 2
> >>> + required:
> >>> + - aspeed,global-regs
> >>
> >> else:
> >> aspeed,global-regs: false
> >> and the same for other v2 properties
> >>
> >
> > Does modify by following?
> >
> > allOf:
> > -if:
> > properties:
> > compatible:
> > contains:
> > const: aspeed,ast2600-i2cv2
> >
> > then:
> > properties:
> > reg:
> > minItems: 2
> > required:
> > - aspeed,global-regs
> > else:
> > - aspeed,global-regs: false
> > -aspeed,timeout: false
> > - aspeed,xfer-mode: false
>
> yes
>
>
>
> Best regards,
> Krzysztof