mfd: core: Make a best effort attempt to match devices with the correct of_nodes

Currently, when a child platform device (sometimes referred to as a
sub-device) is registered via the Multi-Functional Device (MFD) API,
the framework attempts to match the newly registered platform device
with its associated Device Tree (OF) node.  Until now, the device has
been allocated the first node found with an identical OF compatible
string.  Unfortunately, if there are, say for example '3' devices
which are to be handled by the same driver and therefore have the same
compatible string, each of them will be allocated a pointer to the
*first* node.

An example Device Tree entry might look like this:

  mfd_of_test {
          compatible = "mfd,of-test-parent";
          #address-cells = <0x02>;
          #size-cells = <0x02>;

          child@aaaaaaaaaaaaaaaa {
                  compatible = "mfd,of-test-child";
                  reg = <0xaaaaaaaa 0xaaaaaaaa 0 0x11>,
                        <0xbbbbbbbb 0xbbbbbbbb 0 0x22>;
          };

          child@cccccccc {
                  compatible = "mfd,of-test-child";
                  reg = <0x00000000 0xcccccccc 0 0x33>;
          };

          child@dddddddd00000000 {
                  compatible = "mfd,of-test-child";
                  reg = <0xdddddddd 0x00000000 0 0x44>;
          };
  };

When used with example sub-device registration like this:

  static const struct mfd_cell mfd_of_test_cell[] = {
        OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 0, "mfd,of-test-child"),
        OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child"),
        OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child")
  };

... the current implementation will result in all devices being allocated
the first OF node found containing a matching compatible string:

  [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0
  [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@aaaaaaaaaaaaaaaa
  [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
  [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@aaaaaaaaaaaaaaaa
  [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
  [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@aaaaaaaaaaaaaaaa

After this patch each device will be allocated a unique OF node:

  [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0
  [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@aaaaaaaaaaaaaaaa
  [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
  [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@cccccccc
  [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
  [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@dddddddd00000000

Which is fine if all OF nodes are identical.  However if we wish to
apply an attribute to particular device, we really need to ensure the
correct OF node will be associated with the device containing the
correct address.  We accomplish this by matching the device's address
expressed in DT with one provided during sub-device registration.
Like this:

  static const struct mfd_cell mfd_of_test_cell[] = {
        OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child", 0xdddddddd00000000),
        OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child", 0xaaaaaaaaaaaaaaaa),
        OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 3, "mfd,of-test-child", 0x00000000cccccccc)
  };

This will ensure a specific device (designated here using the
platform_ids; 1, 2 and 3) is matched with a particular OF node:

  [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0
  [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@dddddddd00000000
  [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
  [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@aaaaaaaaaaaaaaaa
  [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
  [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@cccccccc

This implementation is still not infallible, hence the mention of
"best effort" in the commit subject.  Since we have not *insisted* on
the existence of 'reg' properties (in some scenarios they just do not
make sense) and no device currently uses the new 'of_reg' attribute,
we have to make an on-the-fly judgement call whether to associate the
OF node anyway.  Which we do in cases where parent drivers haven't
specified a particular OF node to match to.  So there is a *slight*
possibility of the following result (note: the implementation here is
convoluted, but it shows you one means by which this process can
still break):

  /*
   * First entry will match to the first OF node with matching compatible
   * Second will fail, since the first took its OF node and is no longer available
   * Third will succeed
   */
  static const struct mfd_cell mfd_of_test_cell[] = {
        OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child"),
	OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child", 0xaaaaaaaaaaaaaaaa),
        OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 3, "mfd,of-test-child", 0x00000000cccccccc)
  };

The result:

  [0.753869] mfd-of-test-parent mfd_of_test: Registering 3 devices
  [0.756597] mfd-of-test-child: Failed to locate of_node [id: 2]
  [0.759999] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
  [0.760314] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@aaaaaaaaaaaaaaaa
  [0.760908] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
  [0.761183] mfd-of-test-child mfd-of-test-child.2: No OF node associated with this device
  [0.761621] mfd-of-test-child mfd-of-test-child.3: Probing platform device: 3
  [0.761899] mfd-of-test-child mfd-of-test-child.3: Using OF node: child@cccccccc

We could code around this with some pre-parsing semantics, but the
added complexity required to cover each and every corner-case is not
justified.  Merely patching the current failing (via this patch) is
already working with some pretty small corner-cases.  Other issues
should be patched in the parent drivers which can be achieved simply
by implementing OF_MFD_CELL_REG().

Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/mfd-core.c

@@ -10,6 +10,7 @@
 #include <linux/kernel.h>
 #include <linux/platform_device.h>
 #include <linux/acpi.h>
+#include <linux/list.h>
 #include <linux/property.h>
 #include <linux/mfd/core.h>
 #include <linux/pm_runtime.h>
@@ -17,8 +18,17 @@
 #include <linux/module.h>
 #include <linux/irqdomain.h>
 #include <linux/of.h>
+#include <linux/of_address.h>
 #include <linux/regulator/consumer.h>
 
+static LIST_HEAD(mfd_of_node_list);
+
+struct mfd_of_node_entry {
+	struct list_head list;
+	struct device *dev;
+	struct device_node *np;
+};
+
 static struct device_type mfd_dev_type = {
 	.name	= "mfd_device",
 };
@@ -107,6 +117,55 @@ static inline void mfd_acpi_add_device(const struct mfd_cell *cell,
 }
 #endif
 
+static int mfd_match_of_node_to_dev(struct platform_device *pdev,
+				    struct device_node *np,
+				    const struct mfd_cell *cell)
+{
+#if IS_ENABLED(CONFIG_OF)
+	struct mfd_of_node_entry *of_entry;
+	const __be32 *reg;
+	u64 of_node_addr;
+
+	/* Skip devices 'disabled' by Device Tree */
+	if (!of_device_is_available(np))
+		return -ENODEV;
+
+	/* Skip if OF node has previously been allocated to a device */
+	list_for_each_entry(of_entry, &mfd_of_node_list, list)
+		if (of_entry->np == np)
+			return -EAGAIN;
+
+	if (!cell->use_of_reg)
+		/* No of_reg defined - allocate first free compatible match */
+		goto allocate_of_node;
+
+	/* We only care about each node's first defined address */
+	reg = of_get_address(np, 0, NULL, NULL);
+	if (!reg)
+		/* OF node does not contatin a 'reg' property to match to */
+		return -EAGAIN;
+
+	of_node_addr = of_read_number(reg, of_n_addr_cells(np));
+
+	if (cell->of_reg != of_node_addr)
+		/* No match */
+		return -EAGAIN;
+
+allocate_of_node:
+	of_entry = kzalloc(sizeof(*of_entry), GFP_KERNEL);
+	if (!of_entry)
+		return -ENOMEM;
+
+	of_entry->dev = &pdev->dev;
+	of_entry->np = np;
+	list_add_tail(&of_entry->list, &mfd_of_node_list);
+
+	pdev->dev.of_node = np;
+	pdev->dev.fwnode = &np->fwnode;
+#endif
+	return 0;
+}
+
 static int mfd_add_device(struct device *parent, int id,
 			  const struct mfd_cell *cell,
 			  struct resource *mem_base,
@@ -115,6 +174,7 @@ static int mfd_add_device(struct device *parent, int id,
 	struct resource *res;
 	struct platform_device *pdev;
 	struct device_node *np = NULL;
+	struct mfd_of_node_entry *of_entry, *tmp;
 	int ret = -ENOMEM;
 	int platform_id;
 	int r;
@@ -149,19 +209,22 @@ static int mfd_add_device(struct device *parent, int id,
 	if (ret < 0)
 		goto fail_res;
 
-	if (parent->of_node && cell->of_compatible) {
+	if (IS_ENABLED(CONFIG_OF) && parent->of_node && cell->of_compatible) {
 		for_each_child_of_node(parent->of_node, np) {
 			if (of_device_is_compatible(np, cell->of_compatible)) {
-				if (!of_device_is_available(np)) {
+				ret = mfd_match_of_node_to_dev(pdev, np, cell);
-					/* Ignore disabled devices error free */
+				if (ret == -EAGAIN)
-					ret = 0;
+					continue;
+				if (ret)
 					goto fail_alias;
-				}
+
-				pdev->dev.of_node = np;
-				pdev->dev.fwnode = &np->fwnode;
 				break;
 			}
 		}
+
+		if (!pdev->dev.of_node)
+			pr_warn("%s: Failed to locate of_node [id: %d]\n",
+				cell->name, platform_id);
 	}
 
 	mfd_acpi_add_device(cell, pdev);
@@ -170,13 +233,13 @@ static int mfd_add_device(struct device *parent, int id,
 		ret = platform_device_add_data(pdev,
 					cell->platform_data, cell->pdata_size);
 		if (ret)
-			goto fail_alias;
+			goto fail_of_entry;
 	}
 
 	if (cell->properties) {
 		ret = platform_device_add_properties(pdev, cell->properties);
 		if (ret)
-			goto fail_alias;
+			goto fail_of_entry;
 	}
 
 	for (r = 0; r < cell->num_resources; r++) {
@@ -213,18 +276,18 @@ static int mfd_add_device(struct device *parent, int id,
 			if (has_acpi_companion(&pdev->dev)) {
 				ret = acpi_check_resource_conflict(&res[r]);
 				if (ret)
-					goto fail_alias;
+					goto fail_of_entry;
 			}
 		}
 	}
 
 	ret = platform_device_add_resources(pdev, res, cell->num_resources);
 	if (ret)
-		goto fail_alias;
+		goto fail_of_entry;
 
 	ret = platform_device_add(pdev);
 	if (ret)
-		goto fail_alias;
+		goto fail_of_entry;
 
 	if (cell->pm_runtime_no_callbacks)
 		pm_runtime_no_callbacks(&pdev->dev);
@@ -233,6 +296,12 @@ static int mfd_add_device(struct device *parent, int id,
 
 	return 0;
 
+fail_of_entry:
+	list_for_each_entry_safe(of_entry, tmp, &mfd_of_node_list, list)
+		if (of_entry->dev == &pdev->dev) {
+			list_del(&of_entry->list);
+			kfree(of_entry);
+		}
 fail_alias:
 	regulator_bulk_unregister_supply_alias(&pdev->dev,
 					       cell->parent_supplies,
@@ -297,6 +366,8 @@ static int mfd_remove_devices_fn(struct device *dev, void *data)
 	regulator_bulk_unregister_supply_alias(dev, cell->parent_supplies,
 					       cell->num_parent_supplies);
 
+	kfree(cell);
+
 	platform_device_unregister(pdev);
 	return 0;
 }

include/linux/mfd/core.h

@@ -78,6 +78,16 @@ struct mfd_cell {
 	 */
 	const char		*of_compatible;
 
+	/*
+	 * Address as defined in Device Tree.  Used to compement 'of_compatible'
+	 * (above) when matching OF nodes with devices that have identical
+	 * compatible strings
+	 */
+	const u64 of_reg;
+
+	/* Set to 'true' to use 'of_reg' (above) - allows for of_reg=0 */
+	bool use_of_reg;
+
 	/* Matches ACPI */
 	const struct mfd_cell_acpi_match	*acpi_match;