[PATCH 4/5] ACPI / property: Allow holes in reference properties

[Mika Westerberg]

DT allows holes or empty phandles for references. This is used for example
in SPI subsystem where some chip selects are native and others are regular
GPIOs. In ACPI _DSD we currently do not support this but instead the
preceding reference "consumes" all following integer arguments.

For example we would like to support something like the below ASL fragment
for SPI:

  Package () {
      "cs-gpios",
      Package () {
          ^GPIO, 19, 0, 0, // GPIO CS0
          0,               // Native CS
          ^GPIO, 20, 0, 0, // GPIO CS1
      }
  }

The zero in the middle means "no entry" or NULL reference. To support this
we add a new function acpi_node_get_property_reference_fixed_args() that
takes number of expected arguments as parameter. Function returns -ENOENT
if the corresponding index resolves to the "no entry" reference.

Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
---
 drivers/acpi/property.c | 116 +++++++++++++++++++++++++++++++++++-------------
 include/linux/acpi.h    |   3 ++
 2 files changed, 89 insertions(+), 30 deletions(-)

diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
index f2fd3fee588a..b255c4442a05 100644
--- a/drivers/acpi/property.c
+++ b/drivers/acpi/property.c
@@ -472,6 +472,7 @@ static int acpi_data_get_property_array(struct acpi_device_data *data,
  * @data: ACPI device data object containing the property
  * @propname: Name of the property
  * @index: Index of the reference to return
+ * @num_args: Maximum number of arguments after each reference
  * @args: Location to store the returned reference with optional arguments
  *
  * Find property with @name, verifify that it is a package containing at least
@@ -485,8 +486,8 @@ static int acpi_data_get_property_array(struct acpi_device_data *data,
  * Return: %0 on success, negative error code on failure.
  */
 static int acpi_data_get_property_reference(struct acpi_device_data *data,
-					    const char *propname, size_t index,
-					    struct acpi_reference_args *args)
+	const char *propname, size_t index, size_t num_args,
+	struct acpi_reference_args *args)
 {
 	const union acpi_object *element, *end;
 	const union acpi_object *obj;
@@ -532,41 +533,52 @@ static int acpi_data_get_property_reference(struct acpi_device_data *data,
 	while (element < end) {
 		u32 nargs, i;
 
-		if (element->type != ACPI_TYPE_LOCAL_REFERENCE)
-			return -EPROTO;
-
-		ret = acpi_bus_get_device(element->reference.handle, &device);
-		if (ret)
-			return -ENODEV;
-
-		element++;
-		nargs = 0;
-
-		/* assume following integer elements are all args */
-		for (i = 0; element + i < end; i++) {
-			int type = element[i].type;
+		if (element->type == ACPI_TYPE_LOCAL_REFERENCE) {
+			ret = acpi_bus_get_device(element->reference.handle,
+						  &device);
+			if (ret)
+				return -ENODEV;
+
+			nargs = 0;
+			element++;
+
+			/* assume following integer elements are all args */
+			for (i = 0; element + i < end && i < num_args; i++) {
+				int type = element[i].type;
+
+				if (type == ACPI_TYPE_INTEGER)
+					nargs++;
+				else if (type == ACPI_TYPE_LOCAL_REFERENCE)
+					break;
+				else
+					return -EPROTO;
+			}
 
-			if (type == ACPI_TYPE_INTEGER)
-				nargs++;
-			else if (type == ACPI_TYPE_LOCAL_REFERENCE)
-				break;
-			else
+			if (nargs > MAX_ACPI_REFERENCE_ARGS)
 				return -EPROTO;
-		}
 
-		if (idx++ == index) {
-			args->adev = device;
-			args->nargs = nargs;
-			for (i = 0; i < nargs; i++)
-				args->args[i] = element[i].integer.value;
+			if (idx == index) {
+				args->adev = device;
+				args->nargs = nargs;
+				for (i = 0; i < nargs; i++)
+					args->args[i] = element[i].integer.value;
 
-			return 0;
+				return 0;
+			}
+
+			element += nargs;
+		} else if (element->type == ACPI_TYPE_INTEGER) {
+			if (idx == index)
+				return -ENOENT;
+			element++;
+		} else {
+			return -EPROTO;
 		}
 
-		element += nargs;
+		idx++;
 	}
 
-	return -EPROTO;
+	return -ENODATA;
 }
 
 /**
@@ -582,10 +594,54 @@ int acpi_node_get_property_reference(struct fwnode_handle *fwnode,
 {
 	struct acpi_device_data *data = acpi_device_data_of_node(fwnode);
 
-	return data ? acpi_data_get_property_reference(data, name, index, args) : -EINVAL;
+	if (!data)
+		return -EINVAL;
+
+	return acpi_data_get_property_reference(data, name, index,
+		MAX_ACPI_REFERENCE_ARGS, args);
 }
 EXPORT_SYMBOL_GPL(acpi_node_get_property_reference);
 
+/**
+ * acpi_node_get_property_reference_fixed_args - get a reference from property
+ * @fwnode: Firmware node to get the property from.
+ * @propname: Name of the property.
+ * @index: Index of the reference to return.
+ * @num_args: Expected number of arguments following each reference.
+ * @args: Location to store the returned reference with optional arguments.
+ *
+ * Using this function it is possible to leave "holes" in the property
+ * value set like in an example below:
+ *
+ * Package () {
+ *     "cs-gpios",
+ *     Package () {
+ *        ^GPIO, 19, 0, 0,
+ *        ^GPIO, 20, 0, 0,
+ *        0,
+ *        ^GPIO, 21, 0, 0,
+ *     }
+ * }
+ *
+ * Calling this function with index %2 return %-ENOENT and with index %3
+ * returns the last entry. If the property does not contain any more values
+ * %-ENODATA is returned. The NULL entry must be single integer and
+ * preferably contain value %0.
+ */
+int acpi_node_get_property_reference_fixed_args(struct fwnode_handle *fwnode,
+	const char *name, size_t index, size_t num_args,
+	struct acpi_reference_args *args)
+{
+	struct acpi_device_data *data = acpi_device_data_of_node(fwnode);
+
+	if (!data)
+		return -EINVAL;
+
+	return acpi_data_get_property_reference(data, name, index, num_args,
+						args);
+}
+EXPORT_SYMBOL_GPL(acpi_node_get_property_reference_fixed_args);
+
 static int acpi_data_prop_read_single(struct acpi_device_data *data,
 				      const char *propname,
 				      enum dev_prop_type proptype, void *val)
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index c5eaf2f80a4c..c5d7c503843f 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -930,6 +930,9 @@ int acpi_dev_get_property(struct acpi_device *adev, const char *name,
 int acpi_node_get_property_reference(struct fwnode_handle *fwnode,
 				     const char *name, size_t index,
 				     struct acpi_reference_args *args);
+int acpi_node_get_property_reference_fixed_args(struct fwnode_handle *fwnode,
+				const char *name, size_t index, size_t num_args,
+				struct acpi_reference_args *args);
 
 int acpi_node_prop_get(struct fwnode_handle *fwnode, const char *propname,
 		       void **valptr);
-- 
2.9.3