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Date:   Fri, 16 Oct 2020 17:44:08 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: fw_devlink on will break all snps,dw-apb-gpio users

On Thu, Oct 15, 2020 at 8:39 PM Jisheng Zhang
<Jisheng.Zhang@...aptics.com> wrote:
>
> On Thu, 15 Oct 2020 15:08:33 +0100
> Robin Murphy <robin.murphy@....com> wrote:
>
> >
> >
> > On 2020-10-15 10:52, Jisheng Zhang wrote:
> > > On Thu, 15 Oct 2020 01:48:13 -0700
> > > Saravana Kannan <saravanak@...gle.com> wrote:
> > >
> > >> On Thu, Oct 15, 2020 at 1:15 AM Jisheng Zhang
> > >> <Jisheng.Zhang@...aptics.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@...aptics.com> wrote:
> > >>>>>
> > >>>>> On Wed, 14 Oct 2020 10:29:36 -0700
> > >>>>> Saravana Kannan <saravanak@...gle.com> wrote:
> > >>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>> 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).
> > >>>>
> > >>>
> > >>> 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"
> > >>> 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.
> >
> > You appear to be assuming that:
> >
> > A) There a no consumers of DTBs and DT bindings other than Linux.
> > B) No Linux user ever updates their kernel image without also updating
> > their DTB.
> >
> > I can assure you that, in general, neither of those hold true. Hacking
>
> Just my humble opinion, this is fixing rather than hacking DTs.
>
> > DTs to work around internal implementation details in Linux is rarely if
> > ever a good or even viable idea.
> >
>
> I got your opinion. So it looks like modify the dwapb gpio driver is
> avoidable. I will submit patch to do so once 5.10-rc1 is out.
>
> But the device link also introduces below warning for all dw-apb-gpio users:
>
> [    0.016113] OF: /soc/apb@...80000/gpio@...0/gpio-port@1: could not find phandle
> [    0.016197] OF: /soc/apb@...80000/gpio@...0/gpio-port@1: could not find phandle
> [    0.016464] OF: /soc/apb@...80000/gpio@...0/gpio-port@0: could not find phandle
> [    0.016697] OF: /soc/apb@...c0000/gpio@...0/gpio-port@4: could not find phandle
> [    0.017054] OF: /soc/apb@...80000/gpio@...0/gpio-port@1: could not find phandle
> [    0.017128] OF: /soc/apb@...80000/gpio@...0/gpio-port@1: could not find phandle

To clarify, this warning doesn't break any functionality. It's just
fw_devlink not being happy that a property ends in -gpios but doesn't
follow the -gpios format.

You can do both of these then?
1. Update the dwapb gpiodriver so that the older DT still works.

2. Update the DT to not use snps,nr-gpios so that going forward, we
won't be using a deprecated property and causing this warning. Older
DT + newer kernel will have this warning, but that's not the end of
the world.

-Saravana

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