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

From: Jisheng Zhang
Date: Thu Oct 15 2020 - 23:39:59 EST

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In reply to: Robin Murphy: "Re: fw_devlink on will break all snps,dw-apb-gpio users"
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On Thu, 15 Oct 2020 15:08:33 +0100
Robin Murphy <robin.murphy@xxxxxxx> wrote:

>
>
> On 2020-10-15 10:52, Jisheng Zhang wrote:
> > On Thu, 15 Oct 2020 01:48:13 -0700
> > Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
> >
> >> On Thu, Oct 15, 2020 at 1:15 AM Jisheng Zhang
> >> <Jisheng.Zhang@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> wrote:
> >>>>>
> >>>>> On Wed, 14 Oct 2020 10:29:36 -0700
> >>>>> Saravana Kannan <saravanak@xxxxxxxxxx> wrote:
> >>>>>
> >>>>>>
> >>>>>>
> >>>>>> On Wed, Oct 14, 2020 at 4:12 AM Jisheng Zhang
> >>>>>> <Jisheng.Zhang@xxxxxxxxxxxxx> 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"
> >>> 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@f7e80000/gpio@0800/gpio-port@1: could not find phandle
[ 0.016197] OF: /soc/apb@f7e80000/gpio@0c00/gpio-port@1: could not find phandle
[ 0.016464] OF: /soc/apb@f7e80000/gpio@2400/gpio-port@0: could not find phandle
[ 0.016697] OF: /soc/apb@f7fc0000/gpio@8000/gpio-port@4: could not find phandle
[ 0.017054] OF: /soc/apb@f7e80000/gpio@0800/gpio-port@1: could not find phandle
[ 0.017128] OF: /soc/apb@f7e80000/gpio@0c00/gpio-port@1: could not find phandle

Previously, it seems that the solution would be

"let's mark the "snps,nr-gpios" property as
deprecated and add the generic "ngpios" property support with the same
purpose as the deprecated one. That and the errors log above shall
motivate the platform developer to *convert* the DW APB GPIO DT-nodes to
using the standard number of GPIOs property"

as commit 7569486d79ae8ec4 ("gpio: dwapb: Add ngpios DT-property support")
said, the "can't break old DTs" also apply here, it means we need to fix
the warning in device link code rather than fix DTs. Any comments?

Thanks

Next message: Bhaskar Chowdhury: "Re: [PATCH V2] scripts: spelling: Remove space in the entry memry to memory"
Previous message: Andrew Lunn: "Re: Dts for eth network based on marvell's mv88e6390x crashes Xilinx's linux-kernel v5.4"
In reply to: Robin Murphy: "Re: fw_devlink on will break all snps,dw-apb-gpio users"
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