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    SubjectRe: fw_devlink on will break all snps,dw-apb-gpio users
    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");
    > >

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