[PATCH] gpiolib: notify user-space about line state changes triggered by kernel

[PATCH] gpiolib: notify user-space about line state changes triggered by kernel

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

We currently only emit CHANGED_CONFIG events when the user-space changes
GPIO config. We won't be notified if changes come from in-kernel. Let's
call the notifier chain whenever kernel users change direction or any of
the active-low, debounce or consumer name settings. We don't notify the
user-space about the persistence as the uAPI has no notion of it.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/gpio/gpiolib.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 76e0c38026c3..77e0d0afa2b5 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2421,6 +2421,9 @@ int gpiod_direction_input(struct gpio_desc *desc)
 	}
 	if (ret == 0) {
 		clear_bit(FLAG_IS_OUT, &desc->flags);
+		blocking_notifier_call_chain(&desc->gdev->notifier,
+					     GPIO_V2_LINE_CHANGED_CONFIG,
+					     desc);
 		ret = gpio_set_bias(desc);
 	}
 
@@ -2466,8 +2469,12 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value)
 		gc->set(gc, gpio_chip_hwgpio(desc), val);
 	}
 
-	if (!ret)
+	if (!ret) {
 		set_bit(FLAG_IS_OUT, &desc->flags);
+		blocking_notifier_call_chain(&desc->gdev->notifier,
+					     GPIO_V2_LINE_CHANGED_CONFIG,
+					     desc);
+	}
 	trace_gpio_value(desc_to_gpio(desc), 0, val);
 	trace_gpio_direction(desc_to_gpio(desc), 0, ret);
 	return ret;
@@ -2654,9 +2661,15 @@ EXPORT_SYMBOL_GPL(gpiod_set_config);
 int gpiod_set_debounce(struct gpio_desc *desc, unsigned int debounce)
 {
 	unsigned long config;
+	int ret;
 
 	config = pinconf_to_config_packed(PIN_CONFIG_INPUT_DEBOUNCE, debounce);
-	return gpiod_set_config(desc, config);
+	ret = gpiod_set_config(desc, config);
+	if (!ret)
+		blocking_notifier_call_chain(&desc->gdev->notifier,
+					     GPIO_V2_LINE_CHANGED_CONFIG,
+					     desc);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(gpiod_set_debounce);
 
@@ -2705,6 +2718,8 @@ void gpiod_toggle_active_low(struct gpio_desc *desc)
 {
 	VALIDATE_DESC_VOID(desc);
 	change_bit(FLAG_ACTIVE_LOW, &desc->flags);
+	blocking_notifier_call_chain(&desc->gdev->notifier,
+				     GPIO_V2_LINE_CHANGED_CONFIG, desc);
 }
 EXPORT_SYMBOL_GPL(gpiod_toggle_active_low);
 
@@ -3312,6 +3327,8 @@ int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
 
 	kfree_const(desc->label);
 	desc_set_label(desc, name);
+	blocking_notifier_call_chain(&desc->gdev->notifier,
+				     GPIO_V2_LINE_CHANGED_CONFIG, desc);
 
 	return 0;
 }
-- 
2.39.2

Re: [PATCH] gpiolib: notify user-space about line state changes triggered by kernel

[Andy Shevchenko]

On Fri, Aug 18, 2023 at 09:09:44PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Interestingly why you keep submitter and author different...

> We currently only emit CHANGED_CONFIG events when the user-space changes
> GPIO config. We won't be notified if changes come from in-kernel. Let's
> call the notifier chain whenever kernel users change direction or any of
> the active-low, debounce or consumer name settings. We don't notify the
> user-space about the persistence as the uAPI has no notion of it.

...

> -	if (!ret)
> +	if (!ret) {
>  		set_bit(FLAG_IS_OUT, &desc->flags);
> +		blocking_notifier_call_chain(&desc->gdev->notifier,
> +					     GPIO_V2_LINE_CHANGED_CONFIG,
> +					     desc);
> +	}
>  	trace_gpio_value(desc_to_gpio(desc), 0, val);
>  	trace_gpio_direction(desc_to_gpio(desc), 0, ret);
>  	return ret;

The if (!ret) makes me a bit slower to understand as usual pattern to test
for the errors first.

That said, perhaps

	if (ret)
		goto out_trace_event;

	set_bit(FLAG_IS_OUT, &desc->flags);
	blocking_notifier_call_chain(&desc->gdev->notifier,
				     GPIO_V2_LINE_CHANGED_CONFIG, desc);

out_trace_event:
	trace_gpio_value(desc_to_gpio(desc), 0, val);
	trace_gpio_direction(desc_to_gpio(desc), 0, ret);
	return ret;

...

> +	ret = gpiod_set_config(desc, config);
> +	if (!ret)
> +		blocking_notifier_call_chain(&desc->gdev->notifier,
> +					     GPIO_V2_LINE_CHANGED_CONFIG,
> +					     desc);
> +	return ret;

Ditto.

	ret = gpiod_set_config(desc, config);
	if (ret)
		return ret;

	blocking_notifier_call_chain(&desc->gdev->notifier,
				     GPIO_V2_LINE_CHANGED_CONFIG, desc);
	return 0;

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] gpiolib: notify user-space about line state changes triggered by kernel

[Bartosz Golaszewski]

On Mon, Aug 21, 2023 at 12:43 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Fri, Aug 18, 2023 at 09:09:44PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> Interestingly why you keep submitter and author different...
>
> > We currently only emit CHANGED_CONFIG events when the user-space changes
> > GPIO config. We won't be notified if changes come from in-kernel. Let's
> > call the notifier chain whenever kernel users change direction or any of
> > the active-low, debounce or consumer name settings. We don't notify the
> > user-space about the persistence as the uAPI has no notion of it.
>
> ...
>
> > -     if (!ret)
> > +     if (!ret) {
> >               set_bit(FLAG_IS_OUT, &desc->flags);
> > +             blocking_notifier_call_chain(&desc->gdev->notifier,
> > +                                          GPIO_V2_LINE_CHANGED_CONFIG,
> > +                                          desc);
> > +     }
> >       trace_gpio_value(desc_to_gpio(desc), 0, val);
> >       trace_gpio_direction(desc_to_gpio(desc), 0, ret);
> >       return ret;
>
> The if (!ret) makes me a bit slower to understand as usual pattern to test
> for the errors first.
>
> That said, perhaps
>
>         if (ret)
>                 goto out_trace_event;
>
>         set_bit(FLAG_IS_OUT, &desc->flags);
>         blocking_notifier_call_chain(&desc->gdev->notifier,
>                                      GPIO_V2_LINE_CHANGED_CONFIG, desc);
>
> out_trace_event:
>         trace_gpio_value(desc_to_gpio(desc), 0, val);
>         trace_gpio_direction(desc_to_gpio(desc), 0, ret);
>         return ret;
>
> ...
>
> > +     ret = gpiod_set_config(desc, config);
> > +     if (!ret)
> > +             blocking_notifier_call_chain(&desc->gdev->notifier,
> > +                                          GPIO_V2_LINE_CHANGED_CONFIG,
> > +                                          desc);
> > +     return ret;
>
> Ditto.
>
>         ret = gpiod_set_config(desc, config);
>         if (ret)
>                 return ret;
>
>         blocking_notifier_call_chain(&desc->gdev->notifier,
>                                      GPIO_V2_LINE_CHANGED_CONFIG, desc);
>         return 0;
>

I agree with the latter but the former introduces an unnecessary goto
and looks worse IMO.

Bart

> --
> With Best Regards,
> Andy Shevchenko
>
>