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

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Date:   Fri, 12 Feb 2021 20:33:15 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Gross <agross@...nel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 09/10] usb: dwc3: qcom: Detect DWC3 DT-nodes with
 "usb"-prefixed names

On Wed, Feb 10, 2021 at 10:33:26PM +0300, Serge Semin wrote:
> 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@...kalelectronics.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@...kalelectronics.ru>
> > > > > Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.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?

Bjorn, any comment on the question above? So I could respin the series
with this patch updated.

Also note, since the patch's gonna be changed I'll have to remove your
Reviewed-by tag unless u explicitly say I shouldn't.

-Sergey

> 
> -Sergey
> 
> > 
> > Regards,
> > Bjorn