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

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Message-ID: <0be231a2-0c3d-4f18-8de2-3e4f1fe1cd29@linaro.org>
Date: Tue, 30 Jan 2024 17:10:54 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Frank Li <Frank.li@....com>
Cc: Conor Dooley <conor@...nel.org>, 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 30/01/2024 16:20, Frank Li wrote:
> On Tue, Jan 30, 2024 at 08:40:29AM +0100, Krzysztof Kozlowski wrote:
>> 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.
> 
> Sorry, let's correct what my previous said. There are two kinds bus in
> system, one is dma_coherence, the other is none dma_coherence. There are
> some dwc usb core ip, which is the exact the same. Some connect to
> dma_coherence bus, some connect to non-dma_coherence bus.
> 
> So dma_coherence will be varible for this case. we need set *reginfo* for
> dwc usb core, which connnect to dma_coherence bus.  not set "reginfo* for
> the dwc usb core, which connect to none dma_coherence bus.

OK, that makes sense. Please provide link to upstream DTS
(mainline/next/lore link/other upstream projects) showing this.

Best regards,
Krzysztof