linux-kernel - Re: [PATCH 1/2] dt-bindings: spi: Add Socionext F

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Date:   Sat, 19 Nov 2022 01:41:20 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: spi: Add Socionext F_OSPI controller
 bindings

On 2022/11/19 0:36, Mark Brown wrote:
> On Fri, Nov 18, 2022 at 11:16:22PM +0900, Kunihiko Hayashi wrote:
>> On 2022/11/18 20:39, Mark Brown wrote:
>>> On Fri, Nov 18, 2022 at 09:59:03AM +0900, Kunihiko Hayashi wrote:
> 
>>>> +  socionext,cs-start-cycle:
>>>> +  socionext,cs-end-cycle:
>>>> +  socionext,cs-deassert-clk-cycle:
> 
>>> These are all generic SPI properties so we should add them
>>> generically, on the device rather than the controller since this
>>> is something that might vary per client device.  There was also a
>>> core function spi_set_cs_timing() which was in earlier versions
>>> and is about to get reintroduced.
> 
>> So I understand you mean that these properties should be defined like
>> spi-peripheral-props.yaml for the devices.
> 
>> If yes, I'll drop these properties once and define our vendor-specific
>> "peripheral-props" in the next series.
> 
> Yes, sounds good.

Okay, I'll send simple one in v2.

>>>> +    $ref: /schemas/types.yaml#/definitions/uint32-array
>>>> +    items:
>>>> +      - description: the number of bytes to transfer
>>>> +        maximum: 4
>>>> +      - description: value to transfer
>>>> +        default: 0
>>>> +      - description: bit-width to transfer
>>>> +        enum: [0, 1, 2, 4, 8]
> 
>>> This is also something SPI device should set up, as far as I can
>>> tell this should be set vis spi_mem_op.dummy.nbytes.
> 
>> Yes, but the controller also supports dummy cycles, and can send
>> extra bytes before the dummy cycles.
> 
> Ah, so this is some additional thing on top of dummy cycles?  I'd
> not realised that.  It probably wants to be added into spi-mem I
> guess.

Yes, however, it's tough to handle with spi-mem and I don't have
any use case, so drop it.

>>>> +  socionext,data-swap-2byte:
>>>> +    description:
>>>> +      Indicates swap byte order per 2-bytes.
>>>> +    type: boolean
>>>
>>>> +  socionext,data-swap-4byte:
>>>> +    description:
>>>> +      Indicates swap byte order per 4-bytes.
>>>> +    type: boolean
> 
>>> Again these should be set by the device.  I think these should be
>>> set based on a combination of bits per word and if the host is in
>>> big endian or little endian mode.
> 
>> I see. This feature is complicated to use, so I'll not add it here.
> 
> That also works, someone can always add additional support later
> when they have a concrete use case.

I understand.

Thank you,

---
Best Regards
Kunihiko Hayashi