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

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Message-ID: <80d873d4-d813-6c25-8f47-f5ff9af718ec@linaro.org>
Date:   Tue, 21 Feb 2023 10:40:29 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Ryan Chen <ryan_chen@...eedtech.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED i2Cv2

On 21/02/2023 03:43, Ryan Chen wrote:
> Hello Krzysztof,
> 
>> -----Original Message-----
>> From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> Sent: Monday, February 20, 2023 4:35 PM
>> To: Ryan Chen <ryan_chen@...eedtech.com>; Rob Herring
>> <robh+dt@...nel.org>; Krzysztof Kozlowski
>> <krzysztof.kozlowski+dt@...aro.org>; Joel Stanley <joel@....id.au>; Andrew
>> Jeffery <andrew@...id.au>; Philipp Zabel <p.zabel@...gutronix.de>;
>> openbmc@...ts.ozlabs.org; linux-arm-kernel@...ts.infradead.org;
>> linux-aspeed@...ts.ozlabs.org; linux-kernel@...r.kernel.org
>> Subject: Re: [PATCH v5 1/2] dt-bindings: i2c: Add support for ASPEED i2Cv2
>>
>> On 20/02/2023 07:17, Ryan Chen wrote:
>>> AST2600 support new register set for I2Cv2 controller, add bindings
>>> document to support driver of i2cv2 new register mode controller.
>>>
>>> Signed-off-by: Ryan Chen <ryan_chen@...eedtech.com>
>>> ---
>>>  .../devicetree/bindings/i2c/aspeed,i2cv2.yaml | 83
>>> +++++++++++++++++++
>>>  1 file changed, 83 insertions(+)
>>>  create mode 100644
>>> Documentation/devicetree/bindings/i2c/aspeed,i2cv2.yaml
>>
>> New compatible is okay, but as this is the same controller as old one, this
>> should go to old binding.
>>
>> There are several issues anyway here, but I won't reviewing it except few
>> obvious cases.
>>
>>>
>>> diff --git a/Documentation/devicetree/bindings/i2c/aspeed,i2cv2.yaml
>>> b/Documentation/devicetree/bindings/i2c/aspeed,i2cv2.yaml
>>> new file mode 100644
>>> index 000000000000..913fb45d5fbe
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/i2c/aspeed,i2cv2.yaml
>>> @@ -0,0 +1,83 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/i2c/aspeed,i2cv2.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: ASPEED I2Cv2 Controller on the AST26XX SoCs
>>> +
>>> +maintainers:
>>> +  - Ryan Chen <ryan_chen@...eedtech.com>
>>> +
>>> +allOf:
>>> +  - $ref: /schemas/i2c/i2c-controller.yaml#
>>> +
>>> +properties:
>>> +  compatible:
>>> +    enum:
>>> +      - aspeed,ast2600-i2cv2
>>> +
>>> +  reg:
>>> +    minItems: 1
>>> +    items:
>>> +      - description: address offset and range of register
>>> +      - description: address offset and range of buffer register
>>
>> Why this is optional?
> 
> Will modify minItems: 1 to 2
>>
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>> +  clocks:
>>> +    maxItems: 1
>>> +    description:
>>> +      Reference clock for the I2C bus
>>> +
>>> +  resets:
>>> +    maxItems: 1
>>> +
>>> +  clock-frequency:
>>> +    description:
>>> +      Desired I2C bus clock frequency in Hz. default 100khz.
>>> +
>>> +  multi-master:
>>> +    type: boolean
>>> +    description:
>>> +      states that there is another master active on this bus
>>
>> Drop description and type. Just :true.
>>
> Since i2c.txt have multi-master will drop it.
>>> +
>>> +  timeout:
>>> +    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?

> 
>>> +
>>> +  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.
2. And why exactly this is board-specific?



Best regards,
Krzysztof