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

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Date: Tue, 23 Jan 2024 17:23:53 -0500
From: Frank Li <Frank.li@....com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
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 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. 

Frank

> 
> Best regards,
> Krzysztof
>