gpiolib: Allow GPIO chips to request their own GPIOs

Sometimes it is useful to allow GPIO chips themselves to request GPIOs they
own through gpiolib API. One use case is ACPI ASL code that should be able
to toggle GPIOs through GPIO operation regions.

We can't use gpio_request() because it will pin the module to the kernel
forever (it calls try_module_get()). To solve this we move module refcount
manipulation to gpiod_request() and let __gpiod_request() handle the actual
request. This changes the sequence a bit as now try_module_get() is called
outside of gpio_lock (I think this is safe, try_module_get() handles
serialization it needs already).

Then we provide gpiolib internal functions gpiochip_request/free_own_desc()
that do the same as gpio_request() but don't manipulate module refrence
count. This allows the GPIO chip driver to request and free descriptors it
owns without being pinned to the kernel forever.

Signed-off-by: Mika Westerberg <[e-mail]>
Reviewed-by: Alexandre Courbot <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpiolib.c

···
  * on each other, and help provide better diagnostics in debugfs.
  * They're called even less than the "set direction" calls.
  */
-static int gpiod_request(struct gpio_desc *desc, const char *label)
+static int __gpiod_request(struct gpio_desc *desc, const char *label)
 {
-	struct gpio_chip	*chip;
-	int			status = -EPROBE_DEFER;
+	struct gpio_chip	*chip = desc->chip;
+	int			status;
 	unsigned long		flags;
 
-	if (!desc) {
-		pr_warn("%s: invalid GPIO\n", __func__);
-		return -EINVAL;
-	}
-
 	spin_lock_irqsave(&gpio_lock, flags);
-
-	chip = desc->chip;
-	if (chip == NULL)
-		goto done;
-
-	if (!try_module_get(chip->owner))
-		goto done;
 
 	/* NOTE:  gpio_request() can be called in early boot,
 	 * before IRQs are enabled, for non-sleeping (SOC) GPIOs.
···
 		status = 0;
 	} else {
 		status = -EBUSY;
-		module_put(chip->owner);
 		goto done;
 	}
 
···
 
 		if (status < 0) {
 			desc_set_label(desc, NULL);
-			module_put(chip->owner);
 			clear_bit(FLAG_REQUESTED, &desc->flags);
 			goto done;
 		}
···
 		spin_lock_irqsave(&gpio_lock, flags);
 	}
 done:
+	spin_unlock_irqrestore(&gpio_lock, flags);
+	return status;
+}
+
+static int gpiod_request(struct gpio_desc *desc, const char *label)
+{
+	int status = -EPROBE_DEFER;
+	struct gpio_chip *chip;
+
+	if (!desc) {
+		pr_warn("%s: invalid GPIO\n", __func__);
+		return -EINVAL;
+	}
+
+	chip = desc->chip;
+	if (!chip)
+		goto done;
+
+	if (try_module_get(chip->owner)) {
+		status = __gpiod_request(desc, label);
+		if (status < 0)
+			module_put(chip->owner);
+	}
+
+done:
 	if (status)
 		gpiod_dbg(desc, "%s: status %d\n", __func__, status);
-	spin_unlock_irqrestore(&gpio_lock, flags);
+
 	return status;
 }
 
···
 }
 EXPORT_SYMBOL_GPL(gpio_request);
 
-static void gpiod_free(struct gpio_desc *desc)
+static bool __gpiod_free(struct gpio_desc *desc)
 {
+	bool			ret = false;
 	unsigned long		flags;
 	struct gpio_chip	*chip;
 
 	might_sleep();
-
-	if (!desc) {
-		WARN_ON(extra_checks);
-		return;
-	}
 
 	gpiod_unexport(desc);
 
···
 			spin_lock_irqsave(&gpio_lock, flags);
 		}
 		desc_set_label(desc, NULL);
-		module_put(desc->chip->owner);
 		clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
 		clear_bit(FLAG_REQUESTED, &desc->flags);
 		clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
 		clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
-	} else
-		WARN_ON(extra_checks);
+		ret = true;
+	}
 
 	spin_unlock_irqrestore(&gpio_lock, flags);
+	return ret;
+}
+
+static void gpiod_free(struct gpio_desc *desc)
+{
+	if (desc && __gpiod_free(desc))
+		module_put(desc->chip->owner);
+	else
+		WARN_ON(extra_checks);
 }
 
 void gpio_free(unsigned gpio)
···
 }
 EXPORT_SYMBOL_GPL(gpiochip_is_requested);
 
+/**
+ * gpiochip_request_own_desc - Allow GPIO chip to request its own descriptor
+ * @desc: GPIO descriptor to request
+ * @label: label for the GPIO
+ *
+ * Function allows GPIO chip drivers to request and use their own GPIO
+ * descriptors via gpiolib API. Difference to gpiod_request() is that this
+ * function will not increase reference count of the GPIO chip module. This
+ * allows the GPIO chip module to be unloaded as needed (we assume that the
+ * GPIO chip driver handles freeing the GPIOs it has requested).
+ */
+int gpiochip_request_own_desc(struct gpio_desc *desc, const char *label)
+{
+	if (!desc || !desc->chip)
+		return -EINVAL;
+
+	return __gpiod_request(desc, label);
+}
+
+/**
+ * gpiochip_free_own_desc - Free GPIO requested by the chip driver
+ * @desc: GPIO descriptor to free
+ *
+ * Function frees the given GPIO requested previously with
+ * gpiochip_request_own_desc().
+ */
+void gpiochip_free_own_desc(struct gpio_desc *desc)
+{
+	if (desc)
+		__gpiod_free(desc);
+}
 
 /* Drivers MUST set GPIO direction before making get/set calls.  In
  * some cases this is done in early boot, before IRQs are enabled.

drivers/gpio/gpiolib.h

···
 }
 #endif
 
+int gpiochip_request_own_desc(struct gpio_desc *desc, const char *label);
+void gpiochip_free_own_desc(struct gpio_desc *desc);
+
 #endif /* GPIOLIB_H */