linux-kernel - Re: [PATCH net-next V3 1/3] dt-bindings: net: xilinx_axienet: Introduce dmaengine binding support

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Date:   Wed, 17 May 2023 16:48:33 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Gaddam, Sarath Babu Naidu" <sarath.babu.naidu.gaddam@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>
Cc:     "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "Simek, Michal" <michal.simek@....com>,
        "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Sarangi, Anirudha" <anirudha.sarangi@....com>,
        "Katakam, Harini" <harini.katakam@....com>,
        "git (AMD-Xilinx)" <git@....com>
Subject: Re: [PATCH net-next V3 1/3] dt-bindings: net: xilinx_axienet:
 Introduce dmaengine binding support

On 17/05/2023 14:06, Gaddam, Sarath Babu Naidu wrote:
>>>>> +  dma-names:
>>>>> +    items:
>>>>> +      - const: tx_chan0
>>>>
>>>> tx
>>>>
>>>>> +      - const: rx_chan0
>>>>
>>>> rx
>>>
>>> We want to support more channels in the future, currently we support
>>> AXI DMA which has only one tx and rx channel. In future we want to
>>> extend support for multichannel DMA (MCDMA) which has 16 TX and
>>> 16 RX channels. To uniquely identify each channel, we are using chan
>>> suffix. Depending on the usecase AXI ethernet driver can request any
>>> combination of multichannel DMA  channels.
>>>
>>> dma-names = tx_chan0, tx_chan1, rx_chan0, rx_chan1;
>>>
>>> will update the commit message with same.
>>
>> I expect the binding to be complete, otherwise you get comments like this.
>> Add missing parts to the binding and resend.
> 
> Binding is complete for current supported DMA (single channel).  We will
> extend when we add MCDMA.

What doe sit mean "current supported DMA"? By driver? or by hardware? If
the former, then how does it matter for the bindings?

If the latter, then your hardware is going to change? Then you will have
different set of compatibles and then can use different names.

> 
> We will describe the reason for using channel suffix in the description as 
> below. 
> 
>    dma-names:
>       items:
>         - const: tx_chan0
>         - const: rx_chan0
>      description: |
>            Chan suffix is used for identifying each channel uniquely.
>            Current DMA has only one Tx and Rx channel but it will be 
>            extended to support for multichannel DMA (MCDMA) which
>            has 16 TX and 16 RX channels. Depending on the usecase AXI
>            ethernet driver can request any combination of multichannel
>            DMA  channels.

No, because I don't understand what is "will be extended". Bindings
should be complete. If they are going to be extended, it means they are
not complete. If they cannot be complete, which happens, please provide
a reason. There was no reason so far, except your claim it is complete.

Best regards,
Krzysztof