gpio: Add support for hierarchical IRQ domains

Hierarchical IRQ domains can be used to stack different IRQ
controllers on top of each other.

Bring hierarchical IRQ domains into the GPIOLIB core with the
following basic idea:

Drivers that need their interrupts handled hierarchically
specify a callback to translate the child hardware IRQ and
IRQ type for each GPIO offset to a parent hardware IRQ and
parent hardware IRQ type.

Users have to pass the callback, fwnode, and parent irqdomain
before calling gpiochip_irqchip_add().

We use the new method of just filling in the struct
gpio_irq_chip before adding the gpiochip for all hierarchical
irqchips of this type.

The code path for device tree is pretty straight-forward,
while the code path for old boardfiles or anything else will
be more convoluted requireing upfront allocation of the
interrupts when adding the chip.

One specific use-case where this can be useful is if a power
management controller has top-level controls for wakeup
interrupts. In such cases, the power management controller can
be a parent to other interrupt controllers and program
additional registers when an IRQ has its wake capability
enabled or disabled.

The hierarchical irqchip helper code will only be available
when IRQ_DOMAIN_HIERARCHY is selected to GPIO chips using
this should select or depend on that symbol. When using
hierarchical IRQs, the parent interrupt controller must
also be hierarchical all the way up to the top interrupt
controller wireing directly into the CPU, so on systems
that do not have this we can get rid of all the extra
code for supporting hierarchical irqs.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Lina Iyer <ilina@codeaurora.org>
Cc: Jon Hunter <jonathanh@nvidia.com>
Cc: Sowjanya Komatineni <skomatineni@nvidia.com>
Cc: Bitan Biswas <bbiswas@nvidia.com>
Cc: linux-tegra@vger.kernel.org
Cc: David Daney <david.daney@cavium.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Brian Masney <masneyb@onstation.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Brian Masney <masneyb@onstation.org>
Co-developed-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20190808123242.5359-1-linus.walleij@linaro.org

Documentation/driver-api/gpio/driver.rst

@@ -259,7 +259,7 @@ most often cascaded off a parent interrupt controller, and in some special
 cases the GPIO logic is melded with a SoC's primary interrupt controller.
 
 The IRQ portions of the GPIO block are implemented using an irq_chip, using
-the header <linux/irq.h>. So basically such a driver is utilizing two sub-
+the header <linux/irq.h>. So this combined driver is utilizing two sub-
 systems simultaneously: gpio and irq.
 
 It is legal for any IRQ consumer to request an IRQ from any irqchip even if it
@@ -391,25 +391,119 @@ Infrastructure helpers for GPIO irqchips
 ----------------------------------------
 
 To help out in handling the set-up and management of GPIO irqchips and the
-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 a chained cascaded 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-api/driver-model/design-patterns.rst)
+associated irqdomain and resource allocation callbacks. These are activated
+by selecting the Kconfig symbol GPIOLIB_IRQCHIP. If the symbol
+IRQ_DOMAIN_HIERARCHY is also selected, hierarchical helpers will also be
+provided. A big portion of overhead code will be managed by gpiolib,
+under the assumption that your interrupts are 1-to-1-mapped to the
+GPIO line index:
+
+  GPIO line offset   Hardware IRQ
+  0                  0
+  1                  1
+  2                  2
+  ...                ...
+  ngpio-1            ngpio-1
+
+If some GPIO lines do not have corresponding IRQs, the bitmask valid_mask
+and the flag need_valid_mask in gpio_irq_chip can be used to mask off some
+lines as invalid for associating with IRQs.
+
+The preferred way to set up the helpers is to fill in the
+struct gpio_irq_chip inside struct gpio_chip before adding the gpio_chip.
+If you do this, the additional irq_chip will be set up by gpiolib at the
+same time as setting up the rest of the GPIO functionality. The following
+is a typical example of a cascaded interrupt handler using gpio_irq_chip:
+
+  /* Typical state container with dynamic irqchip */
+  struct my_gpio {
+      struct gpio_chip gc;
+      struct irq_chip irq;
+  };
+
+  int irq; /* from platform etc */
+  struct my_gpio *g;
+  struct gpio_irq_chip *girq;
+
+  /* Set up the irqchip dynamically */
+  g->irq.name = "my_gpio_irq";
+  g->irq.irq_ack = my_gpio_ack_irq;
+  g->irq.irq_mask = my_gpio_mask_irq;
+  g->irq.irq_unmask = my_gpio_unmask_irq;
+  g->irq.irq_set_type = my_gpio_set_irq_type;
+
+  /* Get a pointer to the gpio_irq_chip */
+  girq = &g->gc.irq;
+  girq->chip = &g->irq;
+  girq->parent_handler = ftgpio_gpio_irq_handler;
+  girq->num_parents = 1;
+  girq->parents = devm_kcalloc(dev, 1, sizeof(*girq->parents),
+                               GFP_KERNEL);
+  if (!girq->parents)
+      return -ENOMEM;
+  girq->default_type = IRQ_TYPE_NONE;
+  girq->handler = handle_bad_irq;
+  girq->parents[0] = irq;
+
+  return devm_gpiochip_add_data(dev, &g->gc, g);
+
+The helper support using hierarchical interrupt controllers as well.
+In this case the typical set-up will look like this:
+
+  /* Typical state container with dynamic irqchip */
+  struct my_gpio {
+      struct gpio_chip gc;
+      struct irq_chip irq;
+      struct fwnode_handle *fwnode;
+  };
+
+  int irq; /* from platform etc */
+  struct my_gpio *g;
+  struct gpio_irq_chip *girq;
+
+  /* Set up the irqchip dynamically */
+  g->irq.name = "my_gpio_irq";
+  g->irq.irq_ack = my_gpio_ack_irq;
+  g->irq.irq_mask = my_gpio_mask_irq;
+  g->irq.irq_unmask = my_gpio_unmask_irq;
+  g->irq.irq_set_type = my_gpio_set_irq_type;
+
+  /* Get a pointer to the gpio_irq_chip */
+  girq = &g->gc.irq;
+  girq->chip = &g->irq;
+  girq->default_type = IRQ_TYPE_NONE;
+  girq->handler = handle_bad_irq;
+  girq->fwnode = g->fwnode;
+  girq->parent_domain = parent;
+  girq->child_to_parent_hwirq = my_gpio_child_to_parent_hwirq;
+
+  return devm_gpiochip_add_data(dev, &g->gc, g);
+
+As you can see pretty similar, but you do not supply a parent handler for
+the IRQ, instead a parent irqdomain, an fwnode for the hardware and
+a funcion .child_to_parent_hwirq() that has the purpose of looking up
+the parent hardware irq from a child (i.e. this gpio chip) hardware irq.
+As always it is good to look at examples in the kernel tree for advice
+on how to find the required pieces.
+
+The old way of adding irqchips to gpiochips after registration is also still
+available but we try to move away from this:
+
+- DEPRECATED: gpiochip_irqchip_add(): adds a chained cascaded 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)
 
 - gpiochip_irqchip_add_nested(): adds a nested cascaded irqchip to a gpiochip,
   as discussed above regarding different types of cascaded irqchips. The
   cascaded irq has to be handled by a threaded interrupt handler.
   Apart from that it works exactly like the chained irqchip.
 
-- gpiochip_set_chained_irqchip(): sets up a chained cascaded irq handler for a
-  gpio_chip from a parent IRQ and passes the struct gpio_chip* as handler
-  data. Notice that we pass is as the handler data, since the irqchip data is
-  likely used by the parent irqchip.
+- DEPRECATED: gpiochip_set_chained_irqchip(): sets up a chained cascaded irq
+  handler for a gpio_chip from a parent IRQ and passes the struct gpio_chip*
+  as handler data. Notice that we pass is as the handler data, since the
+  irqchip data is likely used by the parent irqchip.
 
 - gpiochip_set_nested_irqchip(): sets up a nested cascaded irq handler for a
   gpio_chip from a parent IRQ. As the parent IRQ has usually been

include/linux/gpio/driver.h

@@ -23,6 +23,9 @@ enum gpio_lookup_flags;
 #ifdef CONFIG_GPIOLIB
 
 #ifdef CONFIG_GPIOLIB_IRQCHIP
+
+struct gpio_chip;
+
 /**
  * struct gpio_irq_chip - GPIO interrupt controller
  */
@@ -49,6 +52,84 @@ struct gpio_irq_chip {
 	 */
 	const struct irq_domain_ops *domain_ops;
 
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+	/**
+	 * @fwnode:
+	 *
+	 * Firmware node corresponding to this gpiochip/irqchip, necessary
+	 * for hierarchical irqdomain support.
+	 */
+	struct fwnode_handle *fwnode;
+
+	/**
+	 * @parent_domain:
+	 *
+	 * If non-NULL, will be set as the parent of this GPIO interrupt
+	 * controller's IRQ domain to establish a hierarchical interrupt
+	 * domain. The presence of this will activate the hierarchical
+	 * interrupt support.
+	 */
+	struct irq_domain *parent_domain;
+
+	/**
+	 * @child_to_parent_hwirq:
+	 *
+	 * This callback translates a child hardware IRQ offset to a parent
+	 * hardware IRQ offset on a hierarchical interrupt chip. The child
+	 * hardware IRQs correspond to the GPIO index 0..ngpio-1 (see the
+	 * ngpio field of struct gpio_chip) and the corresponding parent
+	 * hardware IRQ and type (such as IRQ_TYPE_*) shall be returned by
+	 * the driver. The driver can calculate this from an offset or using
+	 * a lookup table or whatever method is best for this chip. Return
+	 * 0 on successful translation in the driver.
+	 *
+	 * If some ranges of hardware IRQs do not have a corresponding parent
+	 * HWIRQ, return -EINVAL, but also make sure to fill in @valid_mask and
+	 * @need_valid_mask to make these GPIO lines unavailable for
+	 * translation.
+	 */
+	int (*child_to_parent_hwirq)(struct gpio_chip *chip,
+				     unsigned int child_hwirq,
+				     unsigned int child_type,
+				     unsigned int *parent_hwirq,
+				     unsigned int *parent_type);
+
+	/**
+	 * @populate_parent_fwspec:
+	 *
+	 * This optional callback populates the &struct irq_fwspec for the
+	 * parent's IRQ domain. If this is not specified, then
+	 * &gpiochip_populate_parent_fwspec_twocell will be used. A four-cell
+	 * variant named &gpiochip_populate_parent_fwspec_fourcell is also
+	 * available.
+	 */
+	void (*populate_parent_fwspec)(struct gpio_chip *chip,
+				       struct irq_fwspec *fwspec,
+				       unsigned int parent_hwirq,
+				       unsigned int parent_type);
+
+	/**
+	 * @child_offset_to_irq:
+	 *
+	 * This optional callback is used to translate the child's GPIO line
+	 * offset on the GPIO chip to an IRQ number for the GPIO to_irq()
+	 * callback. If this is not specified, then a default callback will be
+	 * provided that returns the line offset.
+	 */
+	unsigned int (*child_offset_to_irq)(struct gpio_chip *chip,
+					    unsigned int pin);
+
+	/**
+	 * @child_irq_domain_ops:
+	 *
+	 * The IRQ domain operations that will be used for this GPIO IRQ
+	 * chip. If no operations are provided, then default callbacks will
+	 * be populated to setup the IRQ hierarchy. Some drivers need to
+	 * supply their own translate function.
+	 */
+	struct irq_domain_ops child_irq_domain_ops;
+#endif
+
 	/**
 	 * @handler:
 	 *
@@ -449,6 +530,36 @@ struct bgpio_pdata {
 	int ngpio;
 };
 
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+
+void gpiochip_populate_parent_fwspec_twocell(struct gpio_chip *chip,
+					     struct irq_fwspec *fwspec,
+					     unsigned int parent_hwirq,
+					     unsigned int parent_type);
+void gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *chip,
+					      struct irq_fwspec *fwspec,
+					      unsigned int parent_hwirq,
+					      unsigned int parent_type);
+
+#else
+
+static void gpiochip_populate_parent_fwspec_twocell(struct gpio_chip *chip,
+						    struct irq_fwspec *fwspec,
+						    unsigned int parent_hwirq,
+						    unsigned int parent_type)
+{
+}
+
+static void gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *chip,
+						     struct irq_fwspec *fwspec,
+						     unsigned int parent_hwirq,
+						     unsigned int parent_type)
+{
+}
+
+#endif /* CONFIG_IRQ_DOMAIN_HIERARCHY */
+
+
 #if IS_ENABLED(CONFIG_GPIO_GENERIC)
 
 int bgpio_init(struct gpio_chip *gc, struct device *dev,