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

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Message-ID: <46781012-2678-4f6c-9aee-b020cabcbb28@linaro.org>
Date: Tue, 23 Jan 2024 22:46:39 +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 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.

Best regards,
Krzysztof