mfd: mfd-core: Add mechanism for removal of a subset of children

Currently, the only way to remove MFD children is with a call to
mfd_remove_devices, which will remove all the children. Under
some circumstances it is useful to remove only a subset of the
child devices. For example if some additional clean up is required
between removal of certain child devices.

To accomplish this a level field is added to mfd_cell, the normal
mfd_remove_devices is modified to not remove devices that are set
to a higher level and a corresponding mfd_remove_devices_late
function is added to remove those children.

See further discussion at:
https://lore.kernel.org/lkml/20200616075834.GF2608702@dell/

Suggested-by: Lee Jones <[e-mail]>
Signed-off-by: Charles Keepax <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/mfd-core.c

···
 {
 	struct platform_device *pdev;
 	const struct mfd_cell *cell;
+	int *level = data;
 
 	if (dev->type != &mfd_dev_type)
 		return 0;
 
 	pdev = to_platform_device(dev);
 	cell = mfd_get_cell(pdev);
+
+	if (level && cell->level > *level)
+		return 0;
 
 	regulator_bulk_unregister_supply_alias(dev, cell->parent_supplies,
 					       cell->num_parent_supplies);
···
 	return 0;
 }
 
+void mfd_remove_devices_late(struct device *parent)
+{
+	int level = MFD_DEP_LEVEL_HIGH;
+
+	device_for_each_child_reverse(parent, &level, mfd_remove_devices_fn);
+}
+EXPORT_SYMBOL(mfd_remove_devices_late);
+
 void mfd_remove_devices(struct device *parent)
 {
-	device_for_each_child_reverse(parent, NULL, mfd_remove_devices_fn);
+	int level = MFD_DEP_LEVEL_NORMAL;
+
+	device_for_each_child_reverse(parent, &level, mfd_remove_devices_fn);
 }
 EXPORT_SYMBOL(mfd_remove_devices);
 

include/linux/mfd/core.h

···
 #define MFD_CELL_NAME(_name) \
 	MFD_CELL_ALL(_name, NULL, NULL, 0, 0, NULL, 0, false, NULL)
 
+#define MFD_DEP_LEVEL_NORMAL 0
+#define MFD_DEP_LEVEL_HIGH 1
+
 struct irq_domain;
 struct property_entry;
 
···
 struct mfd_cell {
 	const char		*name;
 	int			id;
+	int			level;
 
 	int			(*enable)(struct platform_device *dev);
 	int			(*disable)(struct platform_device *dev);
···
 }
 
 extern void mfd_remove_devices(struct device *parent);
+extern void mfd_remove_devices_late(struct device *parent);
 
 extern int devm_mfd_add_devices(struct device *dev, int id,
 				const struct mfd_cell *cells, int n_devs,