gpio: simplify adding threaded interrupts

This tries to simplify the use of CONFIG_GPIOLIB_IRQCHIP when
using threaded interrupts: add a new call
gpiochip_irqchip_add_nested() to indicate that we're dealing
with a nested rather than a chained irqchip, then create a
separate gpiochip_set_nested_irqchip() to mirror
the gpiochip_set_chained_irqchip() call to connect the
parent and child interrupts.

In the nested case gpiochip_set_nested_irqchip() does nothing
more than call irq_set_parent() on each valid child interrupt,
which has little semantic effect in the kernel, but this is
probably still formally correct.

Update all drivers using nested interrupts to use
gpiochip_irqchip_add_nested() so we can now see clearly
which these users are.

The DLN2 driver can drop its specific hack with
.irq_not_threaded as we now recognize whether a chip is
threaded or not from its use of gpiochip_irqchip_add_nested()
signature rather than from inspecting .can_sleep.

We rename the .irq_parent to .irq_chained_parent since this
parent IRQ is only really kept around for the chained
interrupt handlers.

Cc: Lars Poeschel <poeschel@lemonage.de>
Cc: Octavian Purdila <octavian.purdila@intel.com>
Cc: Daniel Baluta <daniel.baluta@intel.com>
Cc: Bin Gao <bin.gao@linux.intel.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Ajay Thomas <ajay.thomas.david.rajamanickam@intel.com>
Cc: Semen Protsenko <semen.protsenko@globallogic.com>
Cc: Alexander Stein <alexander.stein@systec-electronic.com>
Cc: Phil Reid <preid@electromag.com.au>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/gpio/driver.txt

@@ -175,8 +175,8 @@ The IRQ portions of the GPIO block are implemented using an irqchip, using
 the header <linux/irq.h>. So basically such a driver is utilizing two sub-
 systems simultaneously: gpio and irq.
 
-RT_FULL: GPIO driver should not use spinlock_t or any sleepable APIs
-(like PM runtime) as part of its irq_chip implementation on -RT.
+RT_FULL: a realtime compliant GPIO driver should not use spinlock_t or any
+sleepable APIs (like PM runtime) as part of its irq_chip implementation.
 - spinlock_t should be replaced with raw_spinlock_t [1].
 - If sleepable APIs have to be used, these can be done from the .irq_bus_lock()
   and .irq_bus_unlock() callbacks, as these are the only slowpath callbacks
@@ -185,33 +185,32 @@ RT_FULL: GPIO driver should not use spinlock_t or any sleepable APIs
 GPIO irqchips usually fall in one of two categories:
 
 * CHAINED GPIO irqchips: these are usually the type that is embedded on
-  an SoC. This means that there is a fast IRQ handler for the GPIOs that
+  an SoC. This means that there is a fast IRQ flow handler for the GPIOs that
   gets called in a chain from the parent IRQ handler, most typically the
-  system interrupt controller. This means the GPIO irqchip is registered
-  using irq_set_chained_handler() or the corresponding
-  gpiochip_set_chained_irqchip() helper function, and the GPIO irqchip
-  handler will be called immediately from the parent irqchip, while
-  holding the IRQs disabled. The GPIO irqchip will then end up calling
-  something like this sequence in its interrupt handler:
-
-  static irqreturn_t tc3589x_gpio_irq(int irq, void *data)
+  system interrupt controller. This means that the GPIO irqchip handler will
+  be called immediately from the parent irqchip, while holding the IRQs
+  disabled. The GPIO irqchip will then end up calling something like this
+  sequence in its interrupt handler:
+
+  static irqreturn_t foo_gpio_irq(int irq, void *data)
       chained_irq_enter(...);
       generic_handle_irq(...);
       chained_irq_exit(...);
 
   Chained GPIO irqchips typically can NOT set the .can_sleep flag on
-  struct gpio_chip, as everything happens directly in the callbacks.
+  struct gpio_chip, as everything happens directly in the callbacks: no
+  slow bus traffic like I2C can be used.
 
   RT_FULL: Note, chained IRQ handlers will not be forced threaded on -RT.
   As result, spinlock_t or any sleepable APIs (like PM runtime) can't be used
   in chained IRQ handler.
-  if required (and if it can't be converted to the nested threaded GPIO irqchip)
-  - chained IRQ handler can be converted to generic irq handler and this way
-  it will be threaded IRQ handler on -RT and hard IRQ handler on non-RT
+  If required (and if it can't be converted to the nested threaded GPIO irqchip)
+  a chained IRQ handler can be converted to generic irq handler and this way
+  it will be a threaded IRQ handler on -RT and a hard IRQ handler on non-RT
   (for example, see [3]).
   Know W/A: The generic_handle_irq() is expected to be called with IRQ disabled,
-  so IRQ core will complain if it will be called from IRQ handler which is
-  forced thread. The "fake?" raw lock can be used to W/A this problem:
+  so the IRQ core will complain if it is called from an IRQ handler which is
+  forced to a thread. The "fake?" raw lock can be used to W/A this problem:
 
 	raw_spinlock_t wa_lock;
 	static irqreturn_t omap_gpio_irq_handler(int irq, void *gpiobank)
@@ -243,7 +242,7 @@ GPIO irqchips usually fall in one of two categories:
   by the driver. The hallmark of this driver is to call something like
   this in its interrupt handler:
 
-  static irqreturn_t tc3589x_gpio_irq(int irq, void *data)
+  static irqreturn_t foo_gpio_irq(int irq, void *data)
       ...
       handle_nested_irq(irq);
 
@@ -256,23 +255,31 @@ associated irqdomain and resource allocation callbacks, the gpiolib has
 some helpers that can be enabled by selecting the GPIOLIB_IRQCHIP Kconfig
 symbol:
 
-* gpiochip_irqchip_add(): adds an irqchip to a gpiochip. It will pass
+* gpiochip_irqchip_add(): adds a chained irqchip to a gpiochip. It will pass
   the struct gpio_chip* for the chip to all IRQ callbacks, so the callbacks
   need to embed the gpio_chip in its state container and obtain a pointer
   to the container using container_of().
   (See Documentation/driver-model/design-patterns.txt)
 
-  If there is a need to exclude certain GPIOs from the IRQ domain, one can
-  set .irq_need_valid_mask of the gpiochip before gpiochip_add_data() is
-  called. This allocates .irq_valid_mask with as many bits set as there are
-  GPIOs in the chip. Drivers can exclude GPIOs by clearing bits from this
-  mask. The mask must be filled in before gpiochip_irqchip_add() is called.
+* gpiochip_irqchip_add_nested(): adds a nested irqchip to a gpiochip.
+  Apart from that it works exactly like the chained irqchip.
 
 * gpiochip_set_chained_irqchip(): sets up a chained irq handler for a
   gpio_chip from a parent IRQ and passes the struct gpio_chip* as handler
   data. (Notice handler data, since the irqchip data is likely used by the
-  parent irqchip!) This is for the chained type of chip. This is also used
-  to set up a nested irqchip if NULL is passed as handler.
+  parent irqchip!).
+
+* gpiochip_set_nested_irqchip(): sets up a nested irq handler for a
+  gpio_chip from a parent IRQ. As the parent IRQ has usually been
+  explicitly requested by the driver, this does very little more than
+  mark all the child IRQs as having the other IRQ as parent.
+
+If there is a need to exclude certain GPIOs from the IRQ domain, you can
+set .irq_need_valid_mask of the gpiochip before gpiochip_add_data() is
+called. This allocates an .irq_valid_mask with as many bits set as there
+are GPIOs in the chip. Drivers can exclude GPIOs by clearing bits from this
+mask. The mask must be filled in before gpiochip_irqchip_add() or
+gpiochip_irqchip_add_nested() is called.
 
 To use the helpers please keep the following in mind:
 
@@ -323,6 +330,9 @@ When implementing an irqchip inside a GPIO driver, these two functions should
 typically be called in the .startup() and .shutdown() callbacks from the
 irqchip.
 
+When using the gpiolib irqchip helpers, these callback are automatically
+assigned.
+
 Real-Time compliance for GPIO IRQ chips
 ---------------------------------------
 

drivers/gpio/gpio-adnp.c

@@ -468,11 +468,11 @@ static int adnp_irq_setup(struct adnp *adnp)
 		return err;
 	}
 
-	err = gpiochip_irqchip_add(chip,
-				   &adnp_irq_chip,
-				   0,
-				   handle_simple_irq,
-				   IRQ_TYPE_NONE);
+	err = gpiochip_irqchip_add_nested(chip,
+					  &adnp_irq_chip,
+					  0,
+					  handle_simple_irq,
+					  IRQ_TYPE_NONE);
 	if (err) {
 		dev_err(chip->parent,
 			"could not connect irqchip to gpiochip\n");

drivers/gpio/gpio-crystalcove.c

@@ -351,8 +351,8 @@ static int crystalcove_gpio_probe(struct platform_device *pdev)
 		return retval;
 	}
 
-	gpiochip_irqchip_add(&cg->chip, &crystalcove_irqchip, 0,
-			     handle_simple_irq, IRQ_TYPE_NONE);
+	gpiochip_irqchip_add_nested(&cg->chip, &crystalcove_irqchip, 0,
+				    handle_simple_irq, IRQ_TYPE_NONE);
 
 	retval = request_threaded_irq(irq, NULL, crystalcove_gpio_irq_handler,
 				      IRQF_ONESHOT, KBUILD_MODNAME, cg);

drivers/gpio/gpio-dln2.c

@@ -467,7 +467,6 @@ static int dln2_gpio_probe(struct platform_device *pdev)
 	dln2->gpio.base = -1;
 	dln2->gpio.ngpio = pins;
 	dln2->gpio.can_sleep = true;
-	dln2->gpio.irq_not_threaded = true;
 	dln2->gpio.set = dln2_gpio_set;
 	dln2->gpio.get = dln2_gpio_get;
 	dln2->gpio.request = dln2_gpio_request;

drivers/gpio/gpio-max732x.c

@@ -520,20 +520,19 @@ static int max732x_irq_setup(struct max732x_chip *chip,
 				client->irq);
 			return ret;
 		}
-		ret =  gpiochip_irqchip_add(&chip->gpio_chip,
-					    &max732x_irq_chip,
-					    irq_base,
-					    handle_simple_irq,
-					    IRQ_TYPE_NONE);
+		ret =  gpiochip_irqchip_add_nested(&chip->gpio_chip,
+						   &max732x_irq_chip,
+						   irq_base,
+						   handle_simple_irq,
+						   IRQ_TYPE_NONE);
 		if (ret) {
 			dev_err(&client->dev,
 				"could not connect irqchip to gpiochip\n");
 			return ret;
 		}
-		gpiochip_set_chained_irqchip(&chip->gpio_chip,
-					     &max732x_irq_chip,
-					     client->irq,
-					     NULL);
+		gpiochip_set_nested_irqchip(&chip->gpio_chip,
+					    &max732x_irq_chip,
+					    client->irq);
 	}
 
 	return 0;

drivers/gpio/gpio-mcp23s08.c

@@ -473,21 +473,20 @@ static int mcp23s08_irq_setup(struct mcp23s08 *mcp)
 		return err;
 	}
 
-	err =  gpiochip_irqchip_add(chip,
-				    &mcp23s08_irq_chip,
-				    0,
-				    handle_simple_irq,
-				    IRQ_TYPE_NONE);
+	err =  gpiochip_irqchip_add_nested(chip,
+					   &mcp23s08_irq_chip,
+					   0,
+					   handle_simple_irq,
+					   IRQ_TYPE_NONE);
 	if (err) {
 		dev_err(chip->parent,
 			"could not connect irqchip to gpiochip: %d\n", err);
 		return err;
 	}
 
-	gpiochip_set_chained_irqchip(chip,
-				     &mcp23s08_irq_chip,
-				     mcp->irq,
-				     NULL);
+	gpiochip_set_nested_irqchip(chip,
+				    &mcp23s08_irq_chip,
+				    mcp->irq);
 
 	return 0;
 }

drivers/gpio/gpio-pca953x.c

@@ -635,20 +635,20 @@ static int pca953x_irq_setup(struct pca953x_chip *chip,
 			return ret;
 		}
 
-		ret =  gpiochip_irqchip_add(&chip->gpio_chip,
-					    &pca953x_irq_chip,
-					    irq_base,
-					    handle_simple_irq,
-					    IRQ_TYPE_NONE);
+		ret =  gpiochip_irqchip_add_nested(&chip->gpio_chip,
+						   &pca953x_irq_chip,
+						   irq_base,
+						   handle_simple_irq,
+						   IRQ_TYPE_NONE);
 		if (ret) {
 			dev_err(&client->dev,
 				"could not connect irqchip to gpiochip\n");
 			return ret;
 		}
 
-		gpiochip_set_chained_irqchip(&chip->gpio_chip,
-					     &pca953x_irq_chip,
-					     client->irq, NULL);
+		gpiochip_set_nested_irqchip(&chip->gpio_chip,
+					    &pca953x_irq_chip,
+					    client->irq);
 	}
 
 	return 0;

drivers/gpio/gpio-pcf857x.c

@@ -378,9 +378,10 @@ static int pcf857x_probe(struct i2c_client *client,
 
 	/* Enable irqchip if we have an interrupt */
 	if (client->irq) {
-		status = gpiochip_irqchip_add(&gpio->chip, &pcf857x_irq_chip,
-					      0, handle_level_irq,
-					      IRQ_TYPE_NONE);
+		status = gpiochip_irqchip_add_nested(&gpio->chip,
+						     &pcf857x_irq_chip,
+						     0, handle_level_irq,
+						     IRQ_TYPE_NONE);
 		if (status) {
 			dev_err(&client->dev, "cannot add irqchip\n");
 			goto fail;
@@ -393,8 +394,8 @@ static int pcf857x_probe(struct i2c_client *client,
 		if (status)
 			goto fail;
 
-		gpiochip_set_chained_irqchip(&gpio->chip, &pcf857x_irq_chip,
-					     client->irq, NULL);
+		gpiochip_set_nested_irqchip(&gpio->chip, &pcf857x_irq_chip,
+					    client->irq);
 		gpio->irq_parent = client->irq;
 	}
 

drivers/gpio/gpio-stmpe.c

@@ -484,21 +484,20 @@ static int stmpe_gpio_probe(struct platform_device *pdev)
 				if (stmpe_gpio->norequest_mask & BIT(i))
 					clear_bit(i, stmpe_gpio->chip.irq_valid_mask);
 		}
-		ret =  gpiochip_irqchip_add(&stmpe_gpio->chip,
-					    &stmpe_gpio_irq_chip,
-					    0,
-					    handle_simple_irq,
-					    IRQ_TYPE_NONE);
+		ret =  gpiochip_irqchip_add_nested(&stmpe_gpio->chip,
+						   &stmpe_gpio_irq_chip,
+						   0,
+						   handle_simple_irq,
+						   IRQ_TYPE_NONE);
 		if (ret) {
 			dev_err(&pdev->dev,
 				"could not connect irqchip to gpiochip\n");
 			goto out_disable;
 		}
 
-		gpiochip_set_chained_irqchip(&stmpe_gpio->chip,
-					     &stmpe_gpio_irq_chip,
-					     irq,
-					     NULL);
+		gpiochip_set_nested_irqchip(&stmpe_gpio->chip,
+					    &stmpe_gpio_irq_chip,
+					    irq);
 	}
 
 	platform_set_drvdata(pdev, stmpe_gpio);

drivers/gpio/gpio-tc3589x.c

@@ -337,21 +337,20 @@ static int tc3589x_gpio_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	ret =  gpiochip_irqchip_add(&tc3589x_gpio->chip,
-				    &tc3589x_gpio_irq_chip,
-				    0,
-				    handle_simple_irq,
-				    IRQ_TYPE_NONE);
+	ret =  gpiochip_irqchip_add_nested(&tc3589x_gpio->chip,
+					   &tc3589x_gpio_irq_chip,
+					   0,
+					   handle_simple_irq,
+					   IRQ_TYPE_NONE);
 	if (ret) {
 		dev_err(&pdev->dev,
 			"could not connect irqchip to gpiochip\n");
 		return ret;
 	}
 
-	gpiochip_set_chained_irqchip(&tc3589x_gpio->chip,
-				     &tc3589x_gpio_irq_chip,
-				     irq,
-				     NULL);
+	gpiochip_set_nested_irqchip(&tc3589x_gpio->chip,
+				    &tc3589x_gpio_irq_chip,
+				    irq);
 
 	platform_set_drvdata(pdev, tc3589x_gpio);
 

drivers/gpio/gpio-wcove.c

@@ -426,8 +426,8 @@ static int wcove_gpio_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	ret = gpiochip_irqchip_add(&wg->chip, &wcove_irqchip, 0,
-			     handle_simple_irq, IRQ_TYPE_NONE);
+	ret = gpiochip_irqchip_add_nested(&wg->chip, &wcove_irqchip, 0,
+					  handle_simple_irq, IRQ_TYPE_NONE);
 	if (ret) {
 		dev_err(dev, "Failed to add irqchip: %d\n", ret);
 		return ret;