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Date:   Wed, 21 Sep 2022 10:25:31 +0200
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Subject: Re: [RFC V2 PATCH 2/3] dt-bindings: net: xilinx_axienet: Introduce
 dmaengine binding support
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To:     "Pandey, Radhey Shyam" <radhey.shyam.pandey@amd.com>,
        "Gaddam, Sarath Babu Naidu" <sarath.babu.naidu.gaddam@amd.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
        "krzysztof.kozlowski+dt@linaro.org" 
        <krzysztof.kozlowski+dt@linaro.org>,
        "linux@armlinux.org.uk" <linux@armlinux.org.uk>
Cc:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Simek, Michal" <michal.simek@amd.com>,
        "Sarangi, Anirudha" <anirudha.sarangi@amd.com>,
        "Katakam, Harini" <harini.katakam@amd.com>,
        "git@xilinx.com" <git@xilinx.com>, "git (AMD-Xilinx)" <git@amd.com>
References: <20220920055703.13246-1-sarath.babu.naidu.gaddam@amd.com>
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From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <MN0PR12MB5953B2E399B48AC410F4AC2DB74F9@MN0PR12MB5953.namprd12.prod.outlook.com>
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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@40c00000 {
>>>        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