[PATCH] mfd: core: introduce of_node_name for mfd sub devices

[Laxman Dewangan]

Multi Function Devices (MFDs) have multiple sub module whose driver is
developed in different sub-system like GPIO, regulators, RTC, clock etc.
The device tree of such device contains multiple sub-node which contains
the properties of these sub-modules.

The sub module gets of_node handle either by the dev->of_node or by getting
the child node handle from parent DT handle by finding child name on parent's
of_node.

To provide the of_node of sub-module directly, currently there is only one
approach:
- Add compatible value when defining the sub-module in mfd core and
  add this properties when adding DT.

Introduce the of_node_name of each sub devices which is set when defining
the mfd_cells of the sub devices and get the handle of these child node
when adding the mfd_devices by getting the sub-node handle with matching
the node name getting the sub-node handle with matching the node name.

Signed-off-by: Laxman Dewangan <ldewangan@xxxxxxxxxx>
---
Creating this patch based on the discussion on patch
[PATCH 1/4] mfd: add support for AMS AS3722 PMIC
The discussion on above patch is not concluded and want to have
further discussion on this patch.

 Documentation/devicetree/bindings/mfd/mfd-core.txt |   57 ++++++++++++++++++++
 drivers/mfd/mfd-core.c                             |   10 +++-
 include/linux/mfd/core.h                           |    6 ++
 3 files changed, 71 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/mfd/mfd-core.txt

diff --git a/Documentation/devicetree/bindings/mfd/mfd-core.txt b/Documentation/devicetree/bindings/mfd/mfd-core.txt
new file mode 100644
index 0000000..d68c893
--- /dev/null
+++ b/Documentation/devicetree/bindings/mfd/mfd-core.txt
@@ -0,0 +1,57 @@
+MFD DT binding document
+-----------------------
+
+Multi Function Devices (MFDs) have multiple sub module whose driver is developed
+in different sub-system like GPIO, regulators, RTC, clock etc. The device
+tree of such device contains multiple sub-node which contains the properties
+of these sub-modules.
+The sub modules get of_node handle either by the dev->of_node or by getting
+the child node handle from parent DT handle by finding child name on parent's
+of_node.
+To provide the of_node of sub-module directly, there is two approach:
+- Add compatible value when defining the sub-module in mfd core and
+  add this properties when adding DT.
+- Add the of_node_name when defining the sub-module in mfd core and
+  add keep same name of child node when adding DT.
+
+If none of above matches then sub-module driver will not get their of_node
+and they need to derive the method to get their node from parent node.
+
+Examples:
+DT file:
+--------
+	mfd_device_dt {
+		....
+		gpio_child {
+			/* Properties which need by gpio sub module */
+		};
+
+		rtc_child {
+			/* Properties which need by rtc sub module */
+		};
+
+		regulator_child {
+			/* Properties which need by regulator sub module */
+		};
+	};
+
+
+Driver code:
+-----------
+static struct mfd_cell mfd_abc_devs[] = {
+	{
+		.name = "mfd-abc-gpio",
+		.of_node_name = "gpio_child";
+	},
+	{
+		.name = "mfd-abc-regulator",
+		.of_node_name = "regulator_child";
+	},
+	{
+		.name = "mfd-abc-rtc",
+		.of_node_name = "rtc_child";
+	},
+};
+
+Here sub-node names are gpio_child, rtc_child, regulator_child and it is same
+as of_node_name defined in the driver.
diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
index f421586..88836c2 100644
--- a/drivers/mfd/mfd-core.c
+++ b/drivers/mfd/mfd-core.c
@@ -99,9 +99,15 @@ static int mfd_add_device(struct device *parent, int id,
 	pdev->dev.dma_mask = parent->dma_mask;
 	pdev->dev.dma_parms = parent->dma_parms;
 
-	if (parent->of_node && cell->of_compatible) {
+	if (parent->of_node && (cell->of_compatible || cell->of_node_name)) {
 		for_each_child_of_node(parent->of_node, np) {
-			if (of_device_is_compatible(np, cell->of_compatible)) {
+			if (cell->of_compatible &&
+			    of_device_is_compatible(np, cell->of_compatible)) {
+				pdev->dev.of_node = np;
+				break;
+			}
+			if (cell->of_node_name && np->name &&
+			    !strcmp(cell->of_node_name, np->name)) {
 				pdev->dev.of_node = np;
 				break;
 			}
diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
index cebe97e..4cf891f 100644
--- a/include/linux/mfd/core.h
+++ b/include/linux/mfd/core.h
@@ -45,6 +45,12 @@ struct mfd_cell {
 	const char		*of_compatible;
 
 	/*
+	 * Device tree sub-node name.
+	 * See: Documentation/devicetree/bindings/mfd/mfd-core.txt
+	 */
+	const char		*of_node_name;
+
+	/*
 	 * These resources can be specified relative to the parent device.
 	 * For accessing hardware you should use resources from the platform dev
 	 */
-- 
1.7.1.1

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