Re: fw_devlink on will break all snps,dw-apb-gpio users
From: Robin Murphy
Date: Thu Oct 15 2020 - 10:08:39 EST
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" 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.
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
DTs to work around internal implementation details in Linux is rarely if
ever a good or even viable idea.
Robin.
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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