linux-kernel - Re: [PATCH 7/9] dt-bindings: spi: mtk-snfi: add two timing delay property

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Date:   Tue, 29 Nov 2022 08:47:05 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Xiangsheng Hou (侯祥胜) 
        <Xiangsheng.Hou@...iatek.com>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "gch981213@...il.com" <gch981213@...il.com>,
        "vigneshr@...com" <vigneshr@...com>,
        "richard@....at" <richard@....at>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Benliang Zhao (赵本亮) 
        <Benliang.Zhao@...iatek.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Bin Zhang (章斌) <bin.zhang@...iatek.com>
Subject: Re: [PATCH 7/9] dt-bindings: spi: mtk-snfi: add two timing delay
 property

On 29/11/2022 03:50, Xiangsheng Hou (侯祥胜) wrote:

>>> --- a/Documentation/devicetree/bindings/spi/mediatek,spi-mtk-
>>> snfi.yaml
>>> +++ b/Documentation/devicetree/bindings/spi/mediatek,spi-mtk-
>>> snfi.yaml
>>> @@ -55,6 +55,22 @@ properties:
>>>      description: device-tree node of the accompanying ECC engine.
>>>      $ref: /schemas/types.yaml#/definitions/phandle
>>>  
>>> +  rx-sample-delay:
>>
>> No, use existing property, don't invent your own stuff - missing unit
>> suffix. See spi-peripheral-props.yaml.
> Will change to other private property. The read sample delay with
> MediaTek SPI NAND controller can be set with values from 0 to 47.
> However, it`s difficult to say the unit of each vaule, because the unit
> value will be difference with different chip process or different
> corner IC.

Why you cannot use same formula as other SPI drivers for sample-delay?
And divide/multiple by some factor specific to SoC, which is taken from
driver_data?

> 
>>> +    description: Rx delay to sample data with this value, the
>>> valid
>>> +                 values are from 0 to 47. The delay is smaller
>>> than
>>> +                 the rx-latch-latency.
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>
>> Drop $ref.
> Will do.
> 
>>
>>> +    minItems: 0
>>> +    maxItems: 47
>>> +    default: 0
>>> +
>>> +  rx-latch-latency:
>>
>> Same problems. Did you check spi-peripheral-props.yaml or other SPI
>> controller schemas for such property?
>>
>>> +    description: Rx delay to sample data with this value, the
>>> value
>>> +                 unit is clock cycle.
>>
>> I think the unit should be rather time (e.g. us).
>>
> Yes, I checked the spi-peripheral-props.yaml and the delay values are
> described exactly unit with ns or us. However the unit of MediaTek read
> latch latency is clock cycle and it`s difference with different clock
> frequency.

This is fine in such case.

> 
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    enum: [0, 1, 2, 3]
>>> +    default: 0
>>> +

Best regards,
Krzysztof