[PATCH v2 08/10] of/platform: Resolve interrupt references at probe time

[Thierry Reding <thierry.reding@gmail.com>]

Interrupt references are currently resolved very early (when a device is
created). This has the disadvantage that it will fail in cases where the
interrupt parent hasn't been probed and no IRQ domain for it has been
registered yet. To work around that various drivers use explicit
initcall ordering to force interrupt parents to be probed before devices
that need them are created. That's error prone and doesn't always work.
If a platform device uses an interrupt line connected to a different
platform device (such as a GPIO controller), both will be created in the
same batch, and the GPIO controller won't have been probed by its driver
when the depending platform device is created. Interrupt resolution will
fail in that case.

Another common workaround is for drivers to explicitly resolve interrupt
references at probe time. This is suboptimal, however, because it will
require every driver to duplicate the code.

This patch adds support for late interrupt resolution to the platform
driver core, by resolving the references right before a device driver's
.probe() function will be called. This not only delays the resolution
until a much later time (giving interrupt parents a better chance of
being probed in the meantime), but it also allows the platform driver
core to queue the device for deferred probing if the interrupt parent
hasn't registered its IRQ domain yet.

Signed-off-by: Thierry Reding <treding@nvidia.com>
---
Changes in v2:
- split off IRQ parsing into separate function to make code flow simpler
- add comments to point out some aspects of the implementation
- make code idempotent (as pointed out by Grygorii Strashko

 drivers/base/platform.c     |   4 ++
 drivers/of/platform.c       | 107 +++++++++++++++++++++++++++++++++++++++++---
 include/linux/of_platform.h |   7 +++
 3 files changed, 112 insertions(+), 6 deletions(-)

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index 4f8bef3..8dcf835 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -481,6 +481,10 @@ static int platform_drv_probe(struct device *_dev)
 	struct platform_device *dev = to_platform_device(_dev);
 	int ret;
 
+	ret = of_platform_probe(dev);
+	if (ret)
+		return ret;
+
 	if (ACPI_HANDLE(_dev))
 		acpi_dev_pm_attach(_dev, true);
 
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 9b439ac..df6d56e 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -142,7 +142,7 @@ struct platform_device *of_device_alloc(struct device_node *np,
 				  struct device *parent)
 {
 	struct platform_device *dev;
-	int rc, i, num_reg = 0, num_irq;
+	int rc, i, num_reg = 0;
 	struct resource *res, temp_res;
 
 	dev = platform_device_alloc("", -1);
@@ -153,23 +153,21 @@ struct platform_device *of_device_alloc(struct device_node *np,
 	if (of_can_translate_address(np))
 		while (of_address_to_resource(np, num_reg, &temp_res) == 0)
 			num_reg++;
-	num_irq = of_irq_count(np);
 
 	/* Populate the resource table */
-	if (num_irq || num_reg) {
-		res = kzalloc(sizeof(*res) * (num_irq + num_reg), GFP_KERNEL);
+	if (num_reg) {
+		res = kzalloc(sizeof(*res) * num_reg, GFP_KERNEL);
 		if (!res) {
 			platform_device_put(dev);
 			return NULL;
 		}
 
-		dev->num_resources = num_reg + num_irq;
+		dev->num_resources = num_reg;
 		dev->resource = res;
 		for (i = 0; i < num_reg; i++, res++) {
 			rc = of_address_to_resource(np, i, res);
 			WARN_ON(rc);
 		}
-		WARN_ON(of_irq_to_resource_table(np, res, num_irq) != num_irq);
 	}
 
 	dev->dev.of_node = of_node_get(np);
@@ -490,4 +488,101 @@ int of_platform_populate(struct device_node *root,
 	return rc;
 }
 EXPORT_SYMBOL_GPL(of_platform_populate);
+
+/**
+ * of_platform_parse_irq() - parse interrupt resource from device node
+ * @pdev: pointer to platform device
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+static int of_platform_parse_irq(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	unsigned int num_res = pdev->num_resources;
+	struct resource *res = pdev->resource;
+	unsigned int num_irq, num, c;
+	int ret = 0;
+
+	num_irq = of_irq_count(pdev->dev.of_node);
+	if (!num_irq)
+		return 0;
+
+	/*
+	 * Deferred probing may cause this function to be called multiple
+	 * times, so check if all interrupts have been parsed already and
+	 * return early.
+	 */
+	for (c = 0; c < num_irq; c++)
+		if (platform_get_irq(pdev, c) < 0)
+			break;
+
+	if (c == num_irq)
+		return 0;
+
+	num = num_res + num_irq;
+
+	/*
+	 * Note that in case we're called twice on the same device (due to
+	 * deferred probing for example) this will simply be a nop because
+	 * krealloc() returns the input pointer if the size of the memory
+	 * block that it points to is larger than or equal to the new size
+	 * being requested.
+	 */
+	res = krealloc(res, num * sizeof(*res), GFP_KERNEL);
+	if (!res)
+		return -ENOMEM;
+
+	pdev->resource = res;
+	res += num_res;
+
+	/*
+	 * It is possible for this to fail. If so, not that the number of
+	 * resources is not updated, so that the next call to this function
+	 * will parse all interrupts again. Otherwise we can't keep track of
+	 * how many we've parsed so far.
+	 */
+	ret = of_irq_to_resource_table(np, res, num_irq);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * All interrupts are guaranteed to have been parsed and stored in
+	 * the resource table, so the number of resources can now safely be
+	 * updated.
+	 */
+	pdev->num_resources += num_irq;
+
+	return 0;
+}
+
+/**
+ * of_platform_probe() - OF specific initialization at probe time
+ * @pdev: pointer to a platform device
+ *
+ * This function is called by the driver core to perform devicetree-specific
+ * setup for a given platform device at probe time. If a device's resources
+ * as specified in the device tree are not available yet, this function can
+ * return -EPROBE_DEFER and cause the device to be probed again later, when
+ * other drivers that potentially provide the missing resources have been
+ * probed in turn.
+ *
+ * Note that because of the above, all code executed by this function must
+ * be prepared to be run multiple times on the same device (i.e. it must be
+ * idempotent).
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int of_platform_probe(struct platform_device *pdev)
+{
+	int ret;
+
+	if (!pdev->dev.of_node)
+		return 0;
+
+	ret = of_platform_parse_irq(pdev);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
 #endif /* CONFIG_OF_ADDRESS */
diff --git a/include/linux/of_platform.h b/include/linux/of_platform.h
index 05cb4a9..92fc4f6 100644
--- a/include/linux/of_platform.h
+++ b/include/linux/of_platform.h
@@ -72,6 +72,8 @@ extern int of_platform_populate(struct device_node *root,
 				const struct of_device_id *matches,
 				const struct of_dev_auxdata *lookup,
 				struct device *parent);
+
+extern int of_platform_probe(struct platform_device *pdev);
 #else
 static inline int of_platform_populate(struct device_node *root,
 					const struct of_device_id *matches,
@@ -80,6 +82,11 @@ static inline int of_platform_populate(struct device_node *root,
 {
 	return -ENODEV;
 }
+
+static inline int of_platform_probe(struct platform_device *pdev)
+{
+	return 0;
+}
 #endif
 
 #endif	/* _LINUX_OF_PLATFORM_H */
-- 
1.8.4