media: v4l: fwnode: Add a helper function to obtain device / integer references

v4l2_fwnode_reference_parse_int_prop() will find an fwnode such that under
the device's own fwnode, it will follow child fwnodes with the given
property-value pair and return the resulting fwnode.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/v4l2-core/v4l2-fwnode.c

@@ -578,6 +578,293 @@ static int v4l2_fwnode_reference_parse(
 	return ret;
 }
 
+/*
+ * v4l2_fwnode_reference_get_int_prop - parse a reference with integer
+ *					arguments
+ * @fwnode: fwnode to read @prop from
+ * @notifier: notifier for @dev
+ * @prop: the name of the property
+ * @index: the index of the reference to get
+ * @props: the array of integer property names
+ * @nprops: the number of integer property names in @nprops
+ *
+ * First find an fwnode referred to by the reference at @index in @prop.
+ *
+ * Then under that fwnode, @nprops times, for each property in @props,
+ * iteratively follow child nodes starting from fwnode such that they have the
+ * property in @props array at the index of the child node distance from the
+ * root node and the value of that property matching with the integer argument
+ * of the reference, at the same index.
+ *
+ * The child fwnode reched at the end of the iteration is then returned to the
+ * caller.
+ *
+ * The core reason for this is that you cannot refer to just any node in ACPI.
+ * So to refer to an endpoint (easy in DT) you need to refer to a device, then
+ * provide a list of (property name, property value) tuples where each tuple
+ * uniquely identifies a child node. The first tuple identifies a child directly
+ * underneath the device fwnode, the next tuple identifies a child node
+ * underneath the fwnode identified by the previous tuple, etc. until you
+ * reached the fwnode you need.
+ *
+ * An example with a graph, as defined in Documentation/acpi/dsd/graph.txt:
+ *
+ *	Scope (\_SB.PCI0.I2C2)
+ *	{
+ *		Device (CAM0)
+ *		{
+ *			Name (_DSD, Package () {
+ *				ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ *				Package () {
+ *					Package () {
+ *						"compatible",
+ *						Package () { "nokia,smia" }
+ *					},
+ *				},
+ *				ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ *				Package () {
+ *					Package () { "port0", "PRT0" },
+ *				}
+ *			})
+ *			Name (PRT0, Package() {
+ *				ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ *				Package () {
+ *					Package () { "port", 0 },
+ *				},
+ *				ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ *				Package () {
+ *					Package () { "endpoint0", "EP00" },
+ *				}
+ *			})
+ *			Name (EP00, Package() {
+ *				ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ *				Package () {
+ *					Package () { "endpoint", 0 },
+ *					Package () {
+ *						"remote-endpoint",
+ *						Package() {
+ *							\_SB.PCI0.ISP, 4, 0
+ *						}
+ *					},
+ *				}
+ *			})
+ *		}
+ *	}
+ *
+ *	Scope (\_SB.PCI0)
+ *	{
+ *		Device (ISP)
+ *		{
+ *			Name (_DSD, Package () {
+ *				ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ *				Package () {
+ *					Package () { "port4", "PRT4" },
+ *				}
+ *			})
+ *
+ *			Name (PRT4, Package() {
+ *				ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ *				Package () {
+ *					Package () { "port", 4 },
+ *				},
+ *				ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
+ *				Package () {
+ *					Package () { "endpoint0", "EP40" },
+ *				}
+ *			})
+ *
+ *			Name (EP40, Package() {
+ *				ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ *				Package () {
+ *					Package () { "endpoint", 0 },
+ *					Package () {
+ *						"remote-endpoint",
+ *						Package () {
+ *							\_SB.PCI0.I2C2.CAM0,
+ *							0, 0
+ *						}
+ *					},
+ *				}
+ *			})
+ *		}
+ *	}
+ *
+ * From the EP40 node under ISP device, you could parse the graph remote
+ * endpoint using v4l2_fwnode_reference_get_int_prop with these arguments:
+ *
+ *  @fwnode: fwnode referring to EP40 under ISP.
+ *  @prop: "remote-endpoint"
+ *  @index: 0
+ *  @props: "port", "endpoint"
+ *  @nprops: 2
+ *
+ * And you'd get back fwnode referring to EP00 under CAM0.
+ *
+ * The same works the other way around: if you use EP00 under CAM0 as the
+ * fwnode, you'll get fwnode referring to EP40 under ISP.
+ *
+ * The same example in DT syntax would look like this:
+ *
+ * cam: cam0 {
+ *	compatible = "nokia,smia";
+ *
+ *	port {
+ *		port = <0>;
+ *		endpoint {
+ *			endpoint = <0>;
+ *			remote-endpoint = <&isp 4 0>;
+ *		};
+ *	};
+ * };
+ *
+ * isp: isp {
+ *	ports {
+ *		port@4 {
+ *			port = <4>;
+ *			endpoint {
+ *				endpoint = <0>;
+ *				remote-endpoint = <&cam 0 0>;
+ *			};
+ *		};
+ *	};
+ * };
+ *
+ * Return: 0 on success
+ *	   -ENOENT if no entries (or the property itself) were found
+ *	   -EINVAL if property parsing otherwise failed
+ *	   -ENOMEM if memory allocation failed
+ */
+static struct fwnode_handle *v4l2_fwnode_reference_get_int_prop(
+	struct fwnode_handle *fwnode, const char *prop, unsigned int index,
+	const char * const *props, unsigned int nprops)
+{
+	struct fwnode_reference_args fwnode_args;
+	unsigned int *args = fwnode_args.args;
+	struct fwnode_handle *child;
+	int ret;
+
+	/*
+	 * Obtain remote fwnode as well as the integer arguments.
+	 *
+	 * Note that right now both -ENODATA and -ENOENT may signal
+	 * out-of-bounds access. Return -ENOENT in that case.
+	 */
+	ret = fwnode_property_get_reference_args(fwnode, prop, NULL, nprops,
+						 index, &fwnode_args);
+	if (ret)
+		return ERR_PTR(ret == -ENODATA ? -ENOENT : ret);
+
+	/*
+	 * Find a node in the tree under the referred fwnode corresponding to
+	 * the integer arguments.
+	 */
+	fwnode = fwnode_args.fwnode;
+	while (nprops--) {
+		u32 val;
+
+		/* Loop over all child nodes under fwnode. */
+		fwnode_for_each_child_node(fwnode, child) {
+			if (fwnode_property_read_u32(child, *props, &val))
+				continue;
+
+			/* Found property, see if its value matches. */
+			if (val == *args)
+				break;
+		}
+
+		fwnode_handle_put(fwnode);
+
+		/* No property found; return an error here. */
+		if (!child) {
+			fwnode = ERR_PTR(-ENOENT);
+			break;
+		}
+
+		props++;
+		args++;
+		fwnode = child;
+	}
+
+	return fwnode;
+}
+
+/*
+ * v4l2_fwnode_reference_parse_int_props - parse references for async
+ *					   sub-devices
+ * @dev: struct device pointer
+ * @notifier: notifier for @dev
+ * @prop: the name of the property
+ * @props: the array of integer property names
+ * @nprops: the number of integer properties
+ *
+ * Use v4l2_fwnode_reference_get_int_prop to find fwnodes through reference in
+ * property @prop with integer arguments with child nodes matching in properties
+ * @props. Then, set up V4L2 async sub-devices for those fwnodes in the notifier
+ * accordingly.
+ *
+ * While it is technically possible to use this function on DT, it is only
+ * meaningful on ACPI. On Device tree you can refer to any node in the tree but
+ * on ACPI the references are limited to devices.
+ *
+ * Return: 0 on success
+ *	   -ENOENT if no entries (or the property itself) were found
+ *	   -EINVAL if property parsing otherwisefailed
+ *	   -ENOMEM if memory allocation failed
+ */
+static int v4l2_fwnode_reference_parse_int_props(
+	struct device *dev, struct v4l2_async_notifier *notifier,
+	const char *prop, const char * const *props, unsigned int nprops)
+{
+	struct fwnode_handle *fwnode;
+	unsigned int index;
+	int ret;
+
+	for (index = 0; !IS_ERR((fwnode = v4l2_fwnode_reference_get_int_prop(
+					 dev_fwnode(dev), prop, index, props,
+					 nprops))); index++)
+		fwnode_handle_put(fwnode);
+
+	/*
+	 * Note that right now both -ENODATA and -ENOENT may signal
+	 * out-of-bounds access. Return the error in cases other than that.
+	 */
+	if (PTR_ERR(fwnode) != -ENOENT && PTR_ERR(fwnode) != -ENODATA)
+		return PTR_ERR(fwnode);
+
+	ret = v4l2_async_notifier_realloc(notifier,
+					  notifier->num_subdevs + index);
+	if (ret)
+		return -ENOMEM;
+
+	for (index = 0; !IS_ERR((fwnode = v4l2_fwnode_reference_get_int_prop(
+					 dev_fwnode(dev), prop, index, props,
+					 nprops))); index++) {
+		struct v4l2_async_subdev *asd;
+
+		if (WARN_ON(notifier->num_subdevs >= notifier->max_subdevs)) {
+			ret = -EINVAL;
+			goto error;
+		}
+
+		asd = kzalloc(sizeof(struct v4l2_async_subdev), GFP_KERNEL);
+		if (!asd) {
+			ret = -ENOMEM;
+			goto error;
+		}
+
+		notifier->subdevs[notifier->num_subdevs] = asd;
+		asd->match.fwnode.fwnode = fwnode;
+		asd->match_type = V4L2_ASYNC_MATCH_FWNODE;
+		notifier->num_subdevs++;
+	}
+
+	return PTR_ERR(fwnode) == -ENOENT ? 0 : PTR_ERR(fwnode);
+
+error:
+	fwnode_handle_put(fwnode);
+	return ret;
+}
+
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Sakari Ailus <sakari.ailus@linux.intel.com>");
 MODULE_AUTHOR("Sylwester Nawrocki <s.nawrocki@samsung.com>");