linux-kernel - Re: [PATCH v7 1/2] dt-bindings: dma: Add bindings for intel LGM SOC

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Date:   Mon, 2 Nov 2020 22:41:54 +0800
From:   "Reddy, MallikarjunaX" <mallikarjunax.reddy@...ux.intel.com>
To:     Thomas Langer <tlanger@...linear.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Shevchenko, Andriy" <andriy.shevchenko@...el.com>,
        "chuanhua.lei@...ux.intel.com" <chuanhua.lei@...ux.intel.com>,
        "Kim, Cheol Yong" <Cheol.Yong.Kim@...el.com>,
        "Wu, Qiming" <qi-ming.wu@...el.com>,
        "malliamireddy009@...il.com" <malliamireddy009@...il.com>,
        "peter.ujfalusi@...com" <peter.ujfalusi@...com>,
        "Langer, Thomas" <thomas.langer@...el.com>
Subject: Re: [PATCH v7 1/2] dt-bindings: dma: Add bindings for intel LGM SOC

Hi Thomas,
Thanks for the review, my comments inline.

On 10/28/2020 3:24 AM, Thomas Langer wrote:
> Hello Reddy,
>
> I think "Intel" should always be written with a capital "I" (like in the Subject, but except in the binding below)
OK.
>
>> + compatible:
>> +  oneOf:
>> +   - const: intel,lgm-cdma
>> +   - const: intel,lgm-dma2tx
>> +   - const: intel,lgm-dma1rx
>> +   - const: intel,lgm-dma1tx
>> +   - const: intel,lgm-dma0tx
>> +   - const: intel,lgm-dma3
>> +   - const: intel,lgm-toe-dma30
>> +   - const: intel,lgm-toe-dma31
> Bindings are normally not per instance.
> What if next generation chip gets more DMA modules but has no other changes in the HW block?
> What is wrong with
>    - const: intel,lgm-cdma
>    - const: intel,lgm-hdma
> and extra attributes to define the rx/tx restriction (or what do it mean?)?
>  From the driver code I saw that "toe" is also just of type "hdma" and no further differences in code are done.
We had a discussion on the same in the previous patches and Rob Herring 
said Okay using Different compatibles.
below the snippet.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 >>> + compatible:
 >>> +  anyOf:
 >>> +   - const: intel,lgm-cdma
 >>> +   - const: intel,lgm-dma2tx
 >>> +   - const: intel,lgm-dma1rx
 >>> +   - const: intel,lgm-dma1tx
 >>> +   - const: intel,lgm-dma0tx
 >>> +   - const: intel,lgm-dma3
 >>> +   - const: intel,lgm-toe-dma30
 >>> +   - const: intel,lgm-toe-dma31
 >> Please explain why you need so many different compatible strings.
 > This hw dma has 7 DMA instances.
 > Some for datapath, some for memcpy  and some for TOE.
 > Some for TX only, some for RX only, and some for TX/RX(memcpy and ToE).
 >
 > dma TX/RX type we considered as driver specific data of each instance and
 > used different compatible strings for each instance.
 > And also idea is in future if any driver specific data of any particular
 > instance we can handle.
 >
 > Here if dma name and type(tx or rx) will be accepted as devicetree
 > attributes then we can move .name = "toe_dma31", & .type = DMA_TYPE_MCPY
 > to devicetree. So that the compatible strings can be limited to two.
 > intel,lgm-cdma & intel,lgm-hdma .

[Rob]
Different compatibles are okay if the instances are different and we
don't have properties to describe the differences.

For some of what you have in this binding, I think it should be part of
the consumer cells.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
> Best regards,
> Thomas
>