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

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

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?

> 
>>
>>> +
>>> +  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