Re: [PATCH v6 09/10] usb: dwc3: qcom: Detect DWC3 DT-nodes with "usb"-prefixed names

[Bjorn Andersson]

On Wed 10 Feb 12:40 CST 2021, Serge Semin wrote:

> On Wed, Feb 10, 2021 at 12:17:27PM -0600, Rob Herring wrote:
> > On Wed, Feb 10, 2021 at 11:29 AM Serge Semin
> > <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > In accordance with the USB HCD/DRD schema all the USB controllers are
> > > supposed to have DT-nodes named with prefix "^usb(@.*)?".  Since the
> > > existing DT-nodes will be renamed in a subsequent patch let's first make
> > > sure the DWC3 Qualcomm driver supports them and second falls back to the
> > > deprecated naming so not to fail on the legacy DTS-files passed to the
> > > newer kernels.
> > >
> > > Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
> > > Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
> > > ---
> > >  drivers/usb/dwc3/dwc3-qcom.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> > > index c703d552bbcf..49ad8d507d37 100644
> > > --- a/drivers/usb/dwc3/dwc3-qcom.c
> > > +++ b/drivers/usb/dwc3/dwc3-qcom.c
> > > @@ -630,7 +630,8 @@ static int dwc3_qcom_of_register_core(struct platform_device *pdev)
> > >         struct device           *dev = &pdev->dev;
> > >         int                     ret;
> > >
> > > -       dwc3_np = of_get_child_by_name(np, "dwc3");
> > > +       dwc3_np = of_get_child_by_name(np, "usb") ?:
> > > +                 of_get_child_by_name(np, "dwc3");
> > 
> 
> > Is there some reason using compatible instead wouldn't work here?
> 
> I don't know for sure. The fix has been requested in the framework of
> this discussion:
> https://lore.kernel.org/linux-usb/20201020115959.2658-30-Sergey.Semin@xxxxxxxxxxxxxxxxxxxx/#t
> by the driver maintainer Bjorn. To get a firm answer it's better to
> have him asked.

My feedback was simply that it has to catch both cases, I didn't
consider the fact that we have a compatible to match against.

> As I see it having of_get_compatible_child() utilized
> here would also work. At least for the available in kernel dt-files.
> See the affected dts-es in:
> https://lore.kernel.org/linux-usb/20210210172850.20849-11-Sergey.Semin@xxxxxxxxxxxxxxxxxxxx/
> 
> A problem may happen if some older versions of DTS-es had another
> compatible string in the dwc3 sub-node...
> 

Afaict all Qualcomm dts files has "snps,dwc3", so you can match against
that instead.

Regards,
Bjorn