linux-kernel - Re: fw_devlink on will break all snps,dw-apb-gpio users

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Date:   Wed, 14 Oct 2020 22:04:24 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: fw_devlink on will break all snps,dw-apb-gpio users

On Wed, Oct 14, 2020 at 9:02 PM Jisheng Zhang
<Jisheng.Zhang@...aptics.com> wrote:
>
> On Wed, 14 Oct 2020 10:29:36 -0700
> Saravana Kannan <saravanak@...gle.com> wrote:
>
> > CAUTION: Email originated externally, do not click links or open attachments unless you recognize the sender and know the content is safe.
> >
> >
> > On Wed, Oct 14, 2020 at 4:12 AM Jisheng Zhang
> > <Jisheng.Zhang@...aptics.com> wrote:
> > >
> > > Hi,
> > >
> > > If set fw_devlink as on, any consumers of dw apb gpio won't probe.
> > >
> > > The related dts looks like:
> > >
> > > gpio0: gpio@...0 {
> > >        compatible = "snps,dw-apb-gpio";
> > >        #address-cells = <1>;
> > >        #size-cells = <0>;
> > >
> > >        porta: gpio-port@0 {
> > >               compatible = "snps,dw-apb-gpio-port";
> > >               gpio-controller;
> > >               #gpio-cells = <2>;
> > >               ngpios = <32>;
> > >               reg = <0>;
> > >        };
> > > };
> > >
> > > device_foo {
> > >         status = "okay"
> > >         ...;
> > >         reset-gpio = <&porta, 0, GPIO_ACTIVE_HIGH>;
> > > };
> > >
> > > If I change the reset-gpio property to use another kind of gpio phandle,
> > > e.g gpio expander, then device_foo can be probed successfully.
> > >
> > > The gpio expander dt node looks like:
> > >
> > >         expander3: gpio@44 {
> > >                 compatible = "fcs,fxl6408";
> > >                 pinctrl-names = "default";
> > >                 pinctrl-0 = <&expander3_pmux>;
> > >                 reg = <0x44>;
> > >                 gpio-controller;
> > >                 #gpio-cells = <2>;
> > >                 interrupt-parent = <&portb>;
> > >                 interrupts = <23 IRQ_TYPE_NONE>;
> > >                 interrupt-controller;
> > >                 #interrupt-cells = <2>;
> > >         };
> > >
> > > The common pattern looks like the devlink can't cope with suppliers from
> > > child dt node.
> >
> > fw_devlink doesn't have any problem dealing with child devices being
> > suppliers. The problem with your case is that the
> > drivers/gpio/gpio-dwapb.c driver directly parses the child nodes and
> > never creates struct devices for them. If you have a node with
> > compatible string, fw_devlink expects you to create and probe a struct
> > device for it. So change your driver to add the child devices as
> > devices instead of just parsing the node directly and doing stuff with
> > it.
> >
> > Either that, or stop putting "compatible" string in a node if you
> > don't plan to actually treat it as a device -- but that's too late for
> > this driver (it needs to be backward compatible). So change the driver
> > to add of_platform_populate() and write a driver that probes
> > "snps,dw-apb-gpio-port".
> >
>
> Thanks for the information. The "snps,dw-apb-gpio-port" is never used,
> so I just sent out a series to remove it.

I'd actually prefer that you fix the kernel code to actually use it.
So that fw_devlink can be backward compatible (Older DT + new kernel).
The change is pretty trivial (I just have time to do it for you).

-Saravana