Re: [RFC PATCH v2 3/3] dt-bindings: usb: snps,dwc3: add generic-xhci as child

[Rob Herring]

On Mon, Jan 02, 2023 at 02:45:17PM +0900, Jung Daehwan wrote:
> On Thu, Dec 29, 2022 at 11:23:02AM +0100, Krzysztof Kozlowski wrote:
> > On 29/12/2022 10:57, Daehwan Jung wrote:
> > > Currently, dwc3 invokes just xhci platform driver(generic-xhci) without
> > > DT schema even though xhci works as child of dwc3. It makes sense to add
> > > xhci as child of dwc3 with DT schema. It also supports to use another
> > > compatible in xhci platform driver.
> > 
> > You use some driver as an argument for hardware description, which is
> > not what we need. Describe the hardware.
> > 
> 
> OK. I will it on next submission.
> 
> > > 
> > > Signed-off-by: Daehwan Jung <dh10.jung@xxxxxxxxxxx>
> > > ---
> > >  .../devicetree/bindings/usb/snps,dwc3.yaml    | 29 +++++++++++++++++++
> > >  1 file changed, 29 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > > index 6d78048c4613..83ed7c526dba 100644
> > > --- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > > +++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > > @@ -360,8 +360,22 @@ properties:
> > >      description:
> > >        Enable USB remote wakeup.
> > >  
> > > +  "#address-cells":
> > > +    enum: [ 1, 2 ]
> > > +
> > > +  "#size-cells":
> > > +    enum: [ 1, 2 ]
> > > +
> > > +  ranges: true
> > > +
> > >  unevaluatedProperties: false
> > >  
> > > +# Required child node:
> > > +patternProperties:
> > > +  "^usb@[0-9a-f]+$":
> > > +    $ref: generic-xhci.yaml#
> > > +    description: Required child node
> > 
> > DWC does not have another piece of controller as child... DWC is the
> > controller. Not mentioning that you now affect several other devices
> > without describing the total hardware picture (just some drivers which
> > is not that relevant).
> > 
> 
> DWC controller supports USB Host mode and it uses same resource and
> really works as a child. I guess it's same on many SOCs, especially
> mobile..

Yes, and we already support all those platforms just fine without this 
child node. Adding it means we have to then support *both* ways in the 
driver.


> I just want to modify it to work with DT schema (dwc3 -> xhci-plat).
> I think it needs to dicuss more..

Why doesn't it work with the schema?

It's convenient when DT nodes == device drivers, but hardware is messy 
sometimes. Linux (and other OSs) have to deal with that. We can't write 
the DT to reflect the current (and evolving) needs of a particular OS. 

Rob