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

From: Bartosz Golaszewski <[email protected]>

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 <[email protected]>

---
v1 -> v2:
- use the gpiod_line_state_notify() helper
- reorder the code in gpiod_set_debounce() for better readability

 drivers/gpio/gpiolib.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

drivers/gpio/gpiolib.c +0 -0

index 40a0022ea719..1cb7731550ca 100644

drivers/gpio/gpiolib.c +13 -2

@@ -2484,8 +2485,10 @@ 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);
+		gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
+	}
 	trace_gpio_value(desc_to_gpio(desc), 0, val);
 	trace_gpio_direction(desc_to_gpio(desc), 0, ret);
 	return ret;

@@ -2672,9 +2675,16 @@ 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)
+		return ret;
+
+	gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(gpiod_set_debounce);
 

@@ -2723,6 +2733,7 @@ void gpiod_toggle_active_low(struct gpio_desc *desc)
 {
 	VALIDATE_DESC_VOID(desc);
 	change_bit(FLAG_ACTIVE_LOW, &desc->flags);
+	gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
 }
 EXPORT_SYMBOL_GPL(gpiod_toggle_active_low);
 

@@ -3330,6 +3341,7 @@ int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
 
 	kfree_const(desc->label);
 	desc_set_label(desc, name);
+	gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
 
 	return 0;
 }

Signature · 1 line

2.39.2

Quoted 22 lines · Bartosz Golaszewski

From: Bartosz Golaszewski <[email protected]>

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 <[email protected]>

---
v1 -> v2:
- use the gpiod_line_state_notify() helper
- reorder the code in gpiod_set_debounce() for better readability

 drivers/gpio/gpiolib.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

drivers/gpio/gpiolib.c +0 -0

index 40a0022ea719..1cb7731550ca 100644

drivers/gpio/gpiolib.c int gpiod_direction_input(struct gpio_desc *desc) · line 2445

Quoted 7 lines

drivers/gpio/gpiolib.c +1 -0

@@ -2439,6 +2439,7 @@ int gpiod_direction_input(struct gpio_desc *desc)
      }
      if (ret == 0) {
              clear_bit(FLAG_IS_OUT, &desc->flags);
+             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
              ret = gpio_set_bias(desc);
      }
 

gpiod_direction_input() is called by cdev when a line is requested. So requesting a line now creates two events - REQUESTED and HANGED_CONFIG? Even worse - it calls gpiod_direction_input() first, so we will get CHANGED_CONFIG then REQUESTED??

And a config change from cdev can call this and then generate a CHANGED_CONFIG event itself, so again double events.

Same for output and probably debounce too (that one is a bit more convoluted).

Cheers,
Kent.

Quoted 49 lines

drivers/gpio/gpiolib.c +13 -3

@@ -2484,8 +2485,10 @@ 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);
+             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
+     }
      trace_gpio_value(desc_to_gpio(desc), 0, val);
      trace_gpio_direction(desc_to_gpio(desc), 0, ret);
      return ret;

@@ -2672,9 +2675,16 @@ 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)
+             return ret;
+
+     gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
+
+     return 0;
 }
 EXPORT_SYMBOL_GPL(gpiod_set_debounce);
 

@@ -2723,6 +2733,7 @@ void gpiod_toggle_active_low(struct gpio_desc *desc)
 {
      VALIDATE_DESC_VOID(desc);
      change_bit(FLAG_ACTIVE_LOW, &desc->flags);
+     gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
 }
 EXPORT_SYMBOL_GPL(gpiod_toggle_active_low);
 

@@ -3330,6 +3341,7 @@ int gpiod_set_consumer_name(struct gpio_desc *desc, const char *name)
 
      kfree_const(desc->label);
      desc_set_label(desc, name);
+     gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
 
      return 0;
 }
--

2.39.2

Quoted 40 lines · Kent Gibson

Quoted 22 lines · Bartosz Golaszewski

From: Bartosz Golaszewski <[email protected]>

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 <[email protected]>

---
v1 -> v2:
- use the gpiod_line_state_notify() helper
- reorder the code in gpiod_set_debounce() for better readability

 drivers/gpio/gpiolib.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

drivers/gpio/gpiolib.c +0 -0

index 40a0022ea719..1cb7731550ca 100644

drivers/gpio/gpiolib.c int gpiod_direction_input(struct gpio_desc *desc) · line 2445

Quoted 7 lines

drivers/gpio/gpiolib.c +1 -0

@@ -2439,6 +2439,7 @@ int gpiod_direction_input(struct gpio_desc *desc)
      }
      if (ret == 0) {
              clear_bit(FLAG_IS_OUT, &desc->flags);
+             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
              ret = gpio_set_bias(desc);
      }
 

gpiod_direction_input() is called by cdev when a line is requested. So requesting a line now creates two events - REQUESTED and HANGED_CONFIG? Even worse - it calls gpiod_direction_input() first, so we will get CHANGED_CONFIG then REQUESTED??

And a config change from cdev can call this and then generate a CHANGED_CONFIG event itself, so again double events.

Quoted 2 lines

Same for output and probably debounce too (that one is a bit more convoluted).

Ah, should have tested it with user-space too...

Back to the drawing board I guess. May be the reason why we're not doing it in the first place yet.

Quoted 41 lines · Bartosz Golaszewski

Quoted 40 lines · Kent Gibson

Quoted 22 lines · Bartosz Golaszewski

From: Bartosz Golaszewski <[email protected]>

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 <[email protected]>

---
v1 -> v2:
- use the gpiod_line_state_notify() helper
- reorder the code in gpiod_set_debounce() for better readability

 drivers/gpio/gpiolib.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

drivers/gpio/gpiolib.c +0 -0

index 40a0022ea719..1cb7731550ca 100644

drivers/gpio/gpiolib.c int gpiod_direction_input(struct gpio_desc *desc) · line 2445

Quoted 7 lines

drivers/gpio/gpiolib.c +1 -0

@@ -2439,6 +2439,7 @@ int gpiod_direction_input(struct gpio_desc *desc)
      }
      if (ret == 0) {
              clear_bit(FLAG_IS_OUT, &desc->flags);
+             gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
              ret = gpio_set_bias(desc);
      }
 

gpiod_direction_input() is called by cdev when a line is requested. So requesting a line now creates two events - REQUESTED and HANGED_CONFIG? Even worse - it calls gpiod_direction_input() first, so we will get CHANGED_CONFIG then REQUESTED??

And a config change from cdev can call this and then generate a CHANGED_CONFIG event itself, so again double events.

Quoted 8 lines

Quoted 2 lines

Same for output and probably debounce too (that one is a bit more convoluted).

Ah, should have tested it with user-space too...

Back to the drawing board I guess. May be the reason why we're not doing it in the first place yet.

I think we were only looking at it from the userspace PoV, so what constitutes a "change" is only well defined when driven from userspace. This might be difficult to generalise without redefining what "changed" means, or providing cdev with a separate gpiolib API so you can tell whether the change is actually part of a cdev request, or ...

So, yeah - more thought required.

Got a use case that requires this, or just a nice to have?