linux-kernel - RE: [PATCH v2 2/2] dt-bindings: usb: snps,dwc3: Add 'snps,global-regs-starting-offset' quirk

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Date:   Thu, 13 Apr 2023 02:53:45 +0000
From:   Stanley Chang[昌育德] 
        <stanley_chang@...ltek.com>
To:     Rob Herring <robh+dt@...nel.org>
CC:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Felipe Balbi <balbi@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 2/2] dt-bindings: usb: snps,dwc3: Add 'snps,global-regs-starting-offset' quirk


> 
> On Tue, Apr 11, 2023 at 10:30 PM Stanley Chang
> <stanley_chang@...ltek.com> wrote:
> >
> > Add a new 'snps,global-regs-starting-offset' DT to dwc3 core to remap
> > the global register start address
> >
> > The RTK DHC SoCs were designed the global register address offset at
> > 0x8100. The default address is at DWC3_GLOBALS_REGS_START (0xc100).
> > Therefore, add the property of device-tree to adjust this start address.
> >
> > Signed-off-by: Stanley Chang <stanley_chang@...ltek.com>
> > ---
> >  Documentation/devicetree/bindings/usb/snps,dwc3.yaml | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > index be36956af53b..5cbf3b7ded04 100644
> > --- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > +++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > @@ -359,6 +359,13 @@ properties:
> >      items:
> >        enum: [1, 4, 8, 16, 32, 64, 128, 256]
> >
> > +  snps,global-regs-starting-offset:
> > +    description:
> > +      value for remapping global register start address. For some dwc3
> > +      controller, the dwc3 global register start address is not at
> > +      default DWC3_GLOBALS_REGS_START (0xc100). This property is
> added to
> > +      adjust the address.
> 
> We already have 'reg' or using a specific compatible to handle differences. Use
> one of those, not a custom property. Generally, properties should be used for
> things that vary per board, not fixed in a given SoC.
> 
> Rob
> 

The default offset is fixed by macro DWC3_GLOBALS_REGS_START, and it is not specified by reg.
The dwc3/core is a general driver for every dwc3 IP of SoCs,
and vendor's definition and compatible should specify on its parent.
If we add a specific compatible to dwc3/core driver, then it will break this rule.
Therefore, I use a property to adjust this offset. 
If no define this property, it will use default offset. So it will not affect other board.

Thanks,
Stanley