linux-kernel - Re: [PATCH 1/2] dt-bindings: usb: dwc3: Add system bus request info

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Message-ID: <f3811c1f-eff2-4c7b-8cea-6d3115525235@linaro.org>
Date: Tue, 30 Jan 2024 08:40:29 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Frank Li <Frank.li@....com>, Conor Dooley <conor@...nel.org>
Cc: thinh.nguyen@...opsys.com, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, balbi@...nel.org,
 devicetree@...r.kernel.org, gregkh@...uxfoundation.org, imx@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
 mark.rutland@....com, mathias.nyman@...el.com, pku.leo@...il.com,
 sergei.shtylyov@...entembedded.com
Subject: Re: [PATCH 1/2] dt-bindings: usb: dwc3: Add system bus request info

On 29/01/2024 18:41, Frank Li wrote:
> On Mon, Jan 29, 2024 at 04:49:21PM +0000, Conor Dooley wrote:
>> On Mon, Jan 29, 2024 at 10:19:24AM -0500, Frank Li wrote:
>>> On Tue, Jan 23, 2024 at 05:23:53PM -0500, Frank Li wrote:
>>>> On Tue, Jan 23, 2024 at 10:46:39PM +0100, Krzysztof Kozlowski wrote:
>>>>> On 23/01/2024 20:22, Frank Li wrote:
>>>>>> On Tue, Jan 23, 2024 at 06:42:27PM +0000, Conor Dooley wrote:
>>>>>>> On Tue, Jan 23, 2024 at 01:02:21PM -0500, Frank Li wrote:
>>>>>>>> On Tue, Jan 23, 2024 at 05:51:48PM +0000, Conor Dooley wrote:
>>>>>>>>> On Tue, Jan 23, 2024 at 12:49:27PM -0500, Frank Li wrote:
>>>>>>>>>> On Tue, Jan 23, 2024 at 05:27:13PM +0000, Conor Dooley wrote:
>>>>>>>>>>> On Tue, Jan 23, 2024 at 12:02:05PM -0500, Frank Li wrote:
>>>>>>>>>>>> Add device tree binding allow platform overwrite default value of *REQIN in
>>>>>>>>>>>> GSBUSCFG0.
>>>>>>>>>>>
>>>>>>>>>>> Why might a platform actually want to do this? Why does this need to be
>>>>>>>>>>> set at the board level and being aware of which SoC is in use is not
>>>>>>>>>>> sufficient for the driver to set the correct values?
>>>>>>>>>>
>>>>>>>>>> In snps,dwc3.yaml, there are already similary proptery, such as
>>>>>>>>>> snps,incr-burst-type-adjustment. Use this method can keep whole dwc3 usb
>>>>>>>>>> driver keep consistent. And not all platform try enable hardware
>>>>>>>>>> dma_cohenrence. It is configable for difference platform.
>>>>>>>>>
>>>>>>>>> When you say "platform", what do you mean? I understand that term to
>>>>>>>>> mean a combination of board, soc and firmware.
>>>>>>>>
>>>>>>>> In my company's environment, "platform" is "board". I will use "board" in
>>>>>>>> future. Is it big difference here?
>>>>>>>
>>>>>>> Nah, that's close enough that it makes no difference here.
>>>>>>>
>>>>>>> I'd still like an explanation for why a platform would need to actually
>>>>>>> set these properties though, and why information about coherency cannot
>>>>>>> be determined from whether or not the boss the usb controller is on is
>>>>>>> communicated to be dma coherent via the existing devicetree properties
>>>>>>> for that purpose.
>>>>>>
>>>>>> Actually, I am not very clear about reason. I guest maybe treat off power
>>>>>> consumption and performance.
>>>>>>
>>>>>> What's your judgement about proptery, which should be in dts. Such as
>>>>>> reg, clk, reset, dma and irq, which is tighted with SOC. It is the fixed
>>>>>> value for every SOC. The board dts never change these.
>>>>>
>>>>> Then it can be deduced from the compatible and there is no need for new
>>>>> properties.
>>>>
>>>> Okay, I think "*reqinfo" match this. When new Soc(using compatible dwc usb
>>>> controller) appear regardless dma-cohorence or not, connect by AXI3 or
>>>> AXI4, needn't add new propterties. 
>>>
>>> Anyone have objection? I will prepare v2 to fix rob's bot error.
>>
>> I'm not sure what you want me to object to/not object to.
>> Your last message said "needn't add new propterties", seemingly in
>> agreement with Krzysztoff saying that it can be deduced from the
>> compatible. That seems like a good way forward for me.
> 
> Okay, let me clear it again. dwc usb is quite common IP. The below is
> what reason why need "*reginfo* instead of using compatible string.
> 
> 1. *reginfo* property is decscript hardware behevior, which will be changed
> at difference SOC.
> 2. it may change at board level according to if enable dma coherence.

dma coherence is not a board property. Anyway, you said it will never
change in the board.

> 3. dwc core part is quite common, all SOC using common "snps, dwc3" as
> core-part, all soc specific "nxp, dwc3 *", "qcom, dwc3*" is used for glue
> logic part.

And all should be having dedicated compatibles.

> 4. using *reginfo* can reduce add more strange compatible string such as
> "nxp, dwc3-core" ...
> 5. *reginfo* property likes "reg", "clk", and align what Kryzystoff said.
> "reg", "clk" is fixed for specfic SOC. These can help reduce "compatible"
> string number. "reginfo" do the same work as "reg", "clk" ..

So again, reginfo is fixed for specific SoC? So it can be deduced from
compatible.

I don't know what to say more here... so let's be clear that you
understood me:

NAK

Best regards,
Krzysztof