gpio: Retire the explicit gpio irqchip code

Now that all gpiolib irqchip users have been over to use
the irqchip template, we can finally retire the old code
path and leave just one way in to the irqchip: set up the
template when registering the gpio_chip. For a while
we had two code paths for this which was a bit confusing.

This brings this work to a conclusion, there is now one
way of doing this.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Link: https://lore.kernel.org/r/20201019134046.65101-1-linus.walleij@linaro.org

Documentation/driver-api/gpio/driver.rst

@@ -416,7 +416,8 @@ 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:
+is a typical example of a chained cascaded interrupt handler using
+the gpio_irq_chip:
 
 .. code-block:: c
 
@@ -452,7 +453,46 @@ is a typical example of a cascaded interrupt handler using gpio_irq_chip:
 
   return devm_gpiochip_add_data(dev, &g->gc, g);
 
-The helper support using hierarchical interrupt controllers as well.
+The helper supports using threaded interrupts as well. Then you just request
+the interrupt separately and go with it:
+
+.. code-block:: c
+
+  /* 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;
+
+  ret = devm_request_threaded_irq(dev, irq, NULL,
+		irq_thread_fn, IRQF_ONESHOT, "my-chip", g);
+  if (ret < 0)
+	return ret;
+
+  /* Get a pointer to the gpio_irq_chip */
+  girq = &g->gc.irq;
+  girq->chip = &g->irq;
+  /* This will let us handle the parent IRQ in the driver */
+  girq->parent_handler = NULL;
+  girq->num_parents = 0;
+  girq->parents = NULL;
+  girq->default_type = IRQ_TYPE_NONE;
+  girq->handler = handle_bad_irq;
+
+  return devm_gpiochip_add_data(dev, &g->gc, g);
+
+The helper supports using hierarchical interrupt controllers as well.
 In this case the typical set-up will look like this:
 
 .. code-block:: c
@@ -493,25 +533,6 @@ 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-api/driver-model/design-patterns.rst)
-
-- 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_nested_irqchip(): sets up a nested cascaded 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 GPIO lines from the IRQ domain handled by
 these helpers, we can set .irq.need_valid_mask of the gpiochip before
 devm_gpiochip_add_data() or gpiochip_add_data() is called. This allocates an