linux-kernel - Re: [PATCH v3 6/8] usb: dwc3: of-simple: add compatible for rk3328

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Date:   Fri, 5 Feb 2021 12:41:45 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Johan Jonker <jbx6244@...il.com>
Cc:     "heiko@...ech.de" <heiko@...ech.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        devicetree@...r.kernel.org,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 6/8] usb: dwc3: of-simple: add compatible for rk3328

On Fri, Feb 5, 2021 at 5:40 AM Johan Jonker <jbx6244@...il.com> wrote:
>
> From: Cameron Nemo <cnemo@...anota.com>
>
> Add a compatible to be hooked into by the Rockchip rk3328 device tree.
>
> The rk3399 compatible cannot be reused because the rk3328 SoCs may
> require a specialized driver in the future and old device trees must
> remain compatible with newer kernels.

Yes that's important, but...

> Signed-off-by: Cameron Nemo <cnemo@...anota.com>
> Signed-off-by: Johan Jonker <jbx6244@...il.com>
> ---
>  drivers/usb/dwc3/dwc3-of-simple.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/usb/dwc3/dwc3-of-simple.c b/drivers/usb/dwc3/dwc3-of-simple.c
> index e62ecd22b..93bc34328 100644
> --- a/drivers/usb/dwc3/dwc3-of-simple.c
> +++ b/drivers/usb/dwc3/dwc3-of-simple.c
> @@ -171,6 +171,7 @@ static const struct dev_pm_ops dwc3_of_simple_dev_pm_ops = {
>  };
>
>  static const struct of_device_id of_dwc3_simple_match[] = {
> +       { .compatible = "rockchip,rk3328-dwc3" },

Why does this driver need it? In fact, you don't want this driver to
bind to the dwc3 node as we're binding to the 'snps,dwc3' driver.

>         { .compatible = "rockchip,rk3399-dwc3" },

Given the above, you might think we should remove this, but we can't
since there are old dtb's with the dwc3 child node.

Presumably you are getting lucky here (with link order). The kernel
has no logic to decide which driver to bind to if there are 2 matching
drivers. If we did, it would probably be the opposite of what you want
here as we'd pick the most specific match. This driver should probably
bail probe if no dwc3 child node.

Rob