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

[Serge Semin <Sergey.Semin@baikalelectronics.ru>]

On Wed, Feb 10, 2021 at 12:56:59PM -0600, Bjorn Andersson wrote:
> 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@baikalelectronics.ru> 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@baikalelectronics.ru>
> > > > Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> > > > ---
> > > >  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@baikalelectronics.ru/#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@baikalelectronics.ru/
> > 
> > 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.

Ok then. I'll replace of_get_child_by_name() here with
of_get_compatible_child() matching just against "snps,dwc3" in v7. Can you
confirm that noone ever had a Qcom-based hardware described with dts having
the "synopsys,dwc3" compatible used as the DWC USB3 sub-node here? That
string has been marked as deprecated recently because the vendor-prefix
was changed sometime ago, but the original driver still accept it.

Alternatively to be on a safe side we could match against both
compatibles here as Rob suggests. What do you think?

-Sergey

> 
> Regards,
> Bjorn