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Date:   Thu, 15 Oct 2020 17:52:31 +0800
From:   Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To:     Saravana Kannan <saravanak@google.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: fw_devlink on will break all snps,dw-apb-gpio users
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On Thu, 15 Oct 2020 01:48:13 -0700
Saravana Kannan <saravanak@google.com> wrote:

> On Thu, Oct 15, 2020 at 1:15 AM Jisheng Zhang
> <Jisheng.Zhang@synaptics.com> wrote:
> >
> > On Wed, 14 Oct 2020 22:04:24 -0700 Saravana Kannan wrote:
> >  
> > >
> > >
> > > On Wed, Oct 14, 2020 at 9:02 PM Jisheng Zhang
> > > <Jisheng.Zhang@synaptics.com> wrote:  
> > > >
> > > > On Wed, 14 Oct 2020 10:29:36 -0700
> > > > Saravana Kannan <saravanak@google.com> wrote:
> > > >  
> > > > >
> > > > >
> > > > > On Wed, Oct 14, 2020 at 4:12 AM Jisheng Zhang
> > > > > <Jisheng.Zhang@synaptics.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@2400 {
> > > > > >        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).
> > >  
> >
> > I agree the change is trivial, but it will add some useless LoCs like below.  
> 
> It's not useless if it preserves backward compatibility with DT.
> 
> > I'm not sure whether this is acceptable.So add GPIO and DT maintainers to comment.
> >
> > Hi Linus, Rob,
> >
> > Could you please comment? A simple introduction of the problem:
> >
> > As pointed out by Saravana, "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 once we set fw_devlink=on, then any users of gpio-dwapb
> > as below won't be probed.
> >
> > device_foo {
> >          status = "okay"
> >          ...;
> >          reset-gpio = <&porta, 0, GPIO_ACTIVE_HIGH>;
> > };
> >
> > The compatible string "snps,dw-apb-gpio-port" is never used, but it's in
> > the dt-binding since the dw gpio mainlined. I believe the every dw apb
> > users just copy the compatible string in to soc dtsi. So I submit a series
> > to remove the unused "snps,dw-apb-gpio-port" https://lkml.org/lkml/2020/10/14/1186
> > But this will break Older DT + new kernel with fw_devlink on. Which solution
> > is better?
> >
> > If the following patch is acceptable, I can submit it once 5.10-rc1 is out.
> >
> > thanks
> >
> > diff --git a/drivers/gpio/gpio-dwapb.c b/drivers/gpio/gpio-dwapb.c
> > index 1d8d55bd63aa..b8e012e48b59 100644
> > --- a/drivers/gpio/gpio-dwapb.c
> > +++ b/drivers/gpio/gpio-dwapb.c
> > @@ -19,6 +19,7 @@
> >  #include <linux/of_address.h>
> >  #include <linux/of_device.h>
> >  #include <linux/of_irq.h>
> > +#include <linux/of_platform.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/property.h>
> >  #include <linux/reset.h>
> > @@ -694,6 +695,10 @@ static int dwapb_gpio_probe(struct platform_device *pdev)
> >         }
> >         platform_set_drvdata(pdev, gpio);
> >
> > +       err = devm_of_platform_populate(dev);
> > +       if (err)
> > +               goto out_unregister;
> > +
> >         return 0;
> >
> >  out_unregister:
> > @@ -820,6 +825,25 @@ static struct platform_driver dwapb_gpio_driver = {
> >
> >  module_platform_driver(dwapb_gpio_driver);
> >
> > +static const struct of_device_id dwapb_port_of_match[] = {
> > +       { .compatible = "snps,dw-apb-gpio-port" },
> > +       { /* Sentinel */ }
> > +};
> > +
> > +static int dwapb_gpio_port_probe(struct platform_device *pdev)
> > +{
> > +       return 0;  
> 
> No, I'm not asking to do a stub/dummy probe. Move the stuff you do
> inside device_for_each_child_node{} and dwapb_gpio_add_port() into
> this probe function. Those two pieces of code together are effectively
> "probing" a separate gpio controller for each of the child nodes. So
> just create a real struct device (like we do for every other
> "compatible" DT node) and probe each of them properly using the device
> driver core.

Then I believe the modifications are non-trivial. Maybe Linus and Rob
can comment which way is better, fix the dts or modify the gpio-dwapb.c.
Personally, I prefer fixing dts, because this doesn't remove or modify
any used properties or compatible string, it just removes the unused
compatible string.

Thanks


> 
> > +}
> > +
> > +static struct platform_driver dwapb_gpio_port_driver = {
> > +       .driver         = {
> > +               .name   = "gpio-dwapb-port",
> > +               .of_match_table = dwapb_port_of_match,
> > +       },
> > +       .probe          = dwapb_gpio_port_probe,
> > +};
> > +module_platform_driver(dwapb_gpio_port_driver);
> > +
> >  MODULE_LICENSE("GPL");
> >  MODULE_AUTHOR("Jamie Iles");
> >  MODULE_DESCRIPTION("Synopsys DesignWare APB GPIO driver");
> >