linux-kernel - Re: [RFC V2 PATCH 2/3] dt-bindings: net: xilinx_axienet: Introduce dmaengine binding support

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Date:   Wed, 21 Sep 2022 10:25:31 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>,
        "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>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>
Cc:     "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>,
        "Simek, Michal" <michal.simek@....com>,
        "Sarangi, Anirudha" <anirudha.sarangi@....com>,
        "Katakam, Harini" <harini.katakam@....com>,
        "git@...inx.com" <git@...inx.com>, "git (AMD-Xilinx)" <git@....com>
Subject: Re: [RFC V2 PATCH 2/3] dt-bindings: net: xilinx_axienet: Introduce
 dmaengine binding support

On 21/09/2022 10:23, Pandey, Radhey Shyam wrote:
>>>  required:
>>>    - compatible
>>>    - interrupts
>>>    - reg
>>>    - xlnx,rxmem
>>>    - phy-handle
>>> +  - dmas
>>> +  - dma-names
>>>
>>>  additionalProperties: false
>>>
>>> @@ -132,11 +137,13 @@ examples:
>>>      axi_ethernet_eth: ethernet@...00000 {
>>>        compatible = "xlnx,axi-ethernet-1.00.a";
>>>        interrupt-parent = <&microblaze_0_axi_intc>;
>>> -      interrupts = <2>, <0>, <1>;
>>> +      interrupts = <1>;
>>
>> This looks like an ABI break. How do you handle old DTS? Oh wait... you do
>> not handle it at all.
> 
> Yes, this is anticipated ABI break due to major changes in axiethernet
> driver while adopting to dmaengine framework. Same is highlighted
> in commit description - "DT changes are not backward compatible 
> due to major driver restructuring/cleanup done in adopting the 
> dmaengine framework". 
> 
> Some background - Factor out AXI DMA code into separate driver was
> a TODO item (mentioned in driver changelog) and is being done as 
> part of this series. The DMA code is removed from axiethernet driver 
> and ethernet driver now make use of dmaengine framework to 
> communicate with AXIDMA IP.
> 
> When DMA code is removed from axiethernet driver there is limitation
> to support legacy DMA resources binding. One option is to inform
> user to switch to new binding when old DTS is detected? (and at some
> point we have to make this transition and remove dma code).

If you keep ABI non-broken, such message is a good idea.

> Please let us know if there are any other alternative to consider?

You just cannot break ABI just because you want to refactor some code in
driver.


Best regards,
Krzysztof