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[PATCH v4 0/4] OF phandle nexus support + GPIO nexus

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  [PATCH v4 0/4] OF phandle nexus support + GPIO nexus Stephen Boyd <stephen.boyd@linaro.org> - 2017-08-11 17:50 +0200
    [PATCH v4 2/4] of: Support parsing phandle argument lists through a nexus node Stephen Boyd <stephen.boyd@linaro.org> - 2017-08-11 17:50 +0200
    [PATCH v4 3/4] of: unittest: Add phandle remapping test Stephen Boyd <stephen.boyd@linaro.org> - 2017-08-11 17:50 +0200
    [PATCH v4 4/4] gpio: Support gpio nexus dt bindings Stephen Boyd <stephen.boyd@linaro.org> - 2017-08-11 17:50 +0200
    Re: [PATCH v4 0/4] OF phandle nexus support + GPIO nexus Rob Herring <robh+dt@kernel.org> - 2017-08-15 22:40 +0200

#1709757 — [PATCH v4 0/4] OF phandle nexus support + GPIO nexus

This is a continutation of my phandle remapping/nexus node series
from a while ago. I finally got around to writing the documentation
in the spec for this, but it's really rough around the edges and
could use some review/suggestions to get it into shape. Please
review!

This is one small chunk of work related to DT overlays for expansion
boards. It would be good to have a way to expose #<list>-cells types of
providers through a connector in a standard way. So we introduce a way
to make "nexus" nodes for these types of properties to remap the consumer
number space to the other side of the connector's number space. It's
basically a copy of the interrupt nexus implementation, but without
the address space matching design and interrupt-parent walking.

Changes since v3:
 * Added devicetree spec patch
 * Rebased to v4.13-rc1

Changes since v2:
 * Picked up Linus' ack on the gpio core patch
 * Made const stack arrays static (Rob Herring)
 * Used of_property_read_u32() instead of open coding (Rob Herring)

Changes since v1:
 * Addition of optional pass-thru parameter
 * Reduction of strings passed to 1 instead of 3 (or 4 now)
 * Updated gpio patch for the new function signature
 * Updated test-case for new funciton signature and pass-thru parameter
 * Updated kernel-doc to be correct and highlighted difference between this
   API and of_parse_phandle_with_args()

Stephen Boyd (3):
  Document nexus nodes/specifier remapping
  of: Support parsing phandle argument lists through a nexus node
  of: unittest: Add phandle remapping test
  gpio: Support gpio nexus dt bindings

Kernel:
 drivers/gpio/gpiolib-of.c                   |   4 +-
 drivers/of/base.c                           | 184 ++++++++++++++++++++++++++++
 drivers/of/unittest-data/testcases.dts      |  11 ++
 drivers/of/unittest-data/tests-phandle.dtsi |  25 ++++
 drivers/of/unittest.c                       | 120 ++++++++++++++++++
 include/linux/of.h                          |  12 ++
 6 files changed, 354 insertions(+), 2 deletions(-)

Spec:
 source/devicetree-basics.rst | 208 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 208 insertions(+)

-- 
2.7.4

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#1709758 — [PATCH v4 2/4] of: Support parsing phandle argument lists through a nexus node

Platforms like 96boards have a standardized connector/expansion
slot that exposes signals like GPIOs to expansion boards in an
SoC agnostic way. We'd like the DT overlays for the expansion
boards to be written once without knowledge of the SoC on the
other side of the connector. This avoids the unscalable
combinatorial explosion of a different DT overlay for each
expansion board and SoC pair.

We need a way to describe the GPIOs routed through the connector
in an SoC agnostic way. Let's introduce nexus property parsing
into the OF core to do this. This is largely based on the
interrupt nexus support we already have. This allows us to remap
a phandle list in a consumer node (e.g. reset-gpios) through a
connector in a generic way (e.g. via gpio-map). Do this in a
generic routine so that we can remap any sort of variable length
phandle list.

Taking GPIOs as an example, the connector would be a GPIO nexus,
supporting the remapping of a GPIO specifier space to multiple
GPIO providers on the SoC. DT would look as shown below, where
'soc_gpio1' and 'soc_gpio2' are inside the SoC, 'connector' is an
expansion port where boards can be plugged in, and
'expansion_device' is a device on the expansion board.

	soc {
		soc_gpio1: gpio-controller1 {
			#gpio-cells = <2>;
		};

		soc_gpio2: gpio-controller2 {
			#gpio-cells = <2>;
		};
	};

	connector: connector {
		#gpio-cells = <2>;
		gpio-map = <0 0 &soc_gpio1 1 0>,
			   <1 0 &soc_gpio2 4 0>,
			   <2 0 &soc_gpio1 3 0>,
			   <3 0 &soc_gpio2 2 0>;
		gpio-map-mask = <0xf 0x0>;
		gpio-map-pass-thru = <0x0 0x1>
	};

	expansion_device {
		reset-gpios = <&connector 2 GPIO_ACTIVE_LOW>;
	};

The GPIO core would use of_parse_phandle_with_args_map() instead
of of_parse_phandle_with_args() and arrive at the same type of
result, a phandle and argument list. The difference is that the
phandle and arguments will be remapped through the nexus node to
the underlying SoC GPIO controller node. In the example above,
we would remap 'reset-gpios' from <&connector 2 GPIO_ACTIVE_LOW>
to <&soc_gpio1 3 GPIO_ACTIVE_LOW>.

Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
---
 drivers/of/base.c  | 184 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/of.h |  12 ++++
 2 files changed, 196 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 686628d1dfa6..60f15bf56534 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -1366,6 +1366,190 @@ int of_parse_phandle_with_args(const struct device_node *np, const char *list_na
 EXPORT_SYMBOL(of_parse_phandle_with_args);
 
 /**
+ * of_parse_phandle_with_args_map() - Find a node pointed by phandle in a list and remap it
+ * @np:		pointer to a device tree node containing a list
+ * @list_name:	property name that contains a list
+ * @stem_name:	stem of property names that specify phandles' arguments count
+ * @index:	index of a phandle to parse out
+ * @out_args:	optional pointer to output arguments structure (will be filled)
+ *
+ * This function is useful to parse lists of phandles and their arguments.
+ * Returns 0 on success and fills out_args, on error returns appropriate errno
+ * value. The difference between this function and of_parse_phandle_with_args()
+ * is that this API remaps a phandle if the node the phandle points to has
+ * a <@stem_name>-map property.
+ *
+ * Caller is responsible to call of_node_put() on the returned out_args->np
+ * pointer.
+ *
+ * Example:
+ *
+ * phandle1: node1 {
+ *	#list-cells = <2>;
+ * }
+ *
+ * phandle2: node2 {
+ *	#list-cells = <1>;
+ * }
+ *
+ * phandle3: node3 {
+ * 	#list-cells = <1>;
+ * 	list-map = <0 &phandle2 3>,
+ * 		   <1 &phandle2 2>,
+ * 		   <2 &phandle1 5 1>;
+ *	list-map-mask = <0x3>;
+ * };
+ *
+ * node4 {
+ *	list = <&phandle1 1 2 &phandle3 0>;
+ * }
+ *
+ * To get a device_node of the `node2' node you may call this:
+ * of_parse_phandle_with_args(node4, "list", "list", 1, &args);
+ */
+int of_parse_phandle_with_args_map(const struct device_node *np,
+				   const char *list_name,
+				   const char *stem_name,
+				   int index, struct of_phandle_args *out_args)
+{
+	char *cells_name, *map_name = NULL, *mask_name = NULL;
+	char *pass_name = NULL;
+	struct device_node *cur, *new = NULL;
+	const __be32 *map, *mask, *pass;
+	static const __be32 dummy_mask[] = { [0 ... MAX_PHANDLE_ARGS] = ~0 };
+	static const __be32 dummy_pass[] = { [0 ... MAX_PHANDLE_ARGS] = 0 };
+	__be32 initial_match_array[MAX_PHANDLE_ARGS];
+	const __be32 *match_array = initial_match_array;
+	int i, ret, map_len, match;
+	u32 list_size, new_size;
+
+	if (index < 0)
+		return -EINVAL;
+
+	cells_name = kasprintf(GFP_KERNEL, "#%s-cells", stem_name);
+	if (!cells_name)
+		return -ENOMEM;
+
+	ret = -ENOMEM;
+	map_name = kasprintf(GFP_KERNEL, "%s-map", stem_name);
+	if (!map_name)
+		goto free;
+
+	mask_name = kasprintf(GFP_KERNEL, "%s-map-mask", stem_name);
+	if (!mask_name)
+		goto free;
+
+	pass_name = kasprintf(GFP_KERNEL, "%s-map-pass-thru", stem_name);
+	if (!pass_name)
+		goto free;
+
+	ret = __of_parse_phandle_with_args(np, list_name, cells_name, 0, index,
+					   out_args);
+	if (ret)
+		goto free;
+
+	/* Get the #<list>-cells property */
+	cur = out_args->np;
+	ret = of_property_read_u32(cur, cells_name, &list_size);
+	if (ret < 0)
+		goto put;
+
+	/* Precalculate the match array - this simplifies match loop */
+	for (i = 0; i < list_size; i++)
+		initial_match_array[i] = cpu_to_be32(out_args->args[i]);
+
+	ret = -EINVAL;
+	while (cur) {
+		/* Get the <list>-map property */
+		map = of_get_property(cur, map_name, &map_len);
+		if (!map) {
+			ret = 0;
+			goto free;
+		}
+		map_len /= sizeof(u32);
+
+		/* Get the <list>-map-mask property (optional) */
+		mask = of_get_property(cur, mask_name, NULL);
+		if (!mask)
+			mask = dummy_mask;
+		/* Iterate through <list>-map property */
+		match = 0;
+		while (map_len > (list_size + 1) && !match) {
+			/* Compare specifiers */
+			match = 1;
+			for (i = 0; i < list_size; i++, map_len--)
+				match &= !((match_array[i] ^ *map++) & mask[i]);
+
+			of_node_put(new);
+			new = of_find_node_by_phandle(be32_to_cpup(map));
+			map++;
+			map_len--;
+
+			/* Check if not found */
+			if (!new)
+				goto put;
+
+			if (!of_device_is_available(new))
+				match = 0;
+
+			ret = of_property_read_u32(new, cells_name, &new_size);
+			if (ret)
+				goto put;
+
+			/* Check for malformed properties */
+			if (WARN_ON(new_size > MAX_PHANDLE_ARGS))
+				goto put;
+			if (map_len < new_size)
+				goto put;
+
+			/* Move forward by new node's #<list>-cells amount */
+			map += new_size;
+			map_len -= new_size;
+		}
+		if (!match)
+			goto put;
+
+		/* Get the <list>-map-pass-thru property (optional) */
+		pass = of_get_property(cur, pass_name, NULL);
+		if (!pass)
+			pass = dummy_pass;
+
+		/*
+		 * Successfully parsed a <list>-map translation; copy new
+		 * specifier into the out_args structure, keeping the
+		 * bits specified in <list>-map-pass-thru.
+		 */
+		match_array = map - new_size;
+		for (i = 0; i < new_size; i++) {
+			__be32 val = *(map - new_size + i);
+
+			if (i < list_size) {
+				val &= ~pass[i];
+				val |= cpu_to_be32(out_args->args[i]) & pass[i];
+			}
+
+			out_args->args[i] = be32_to_cpu(val);
+		}
+		out_args->args_count = list_size = new_size;
+		/* Iterate again with new provider */
+		out_args->np = new;
+		of_node_put(cur);
+		cur = new;
+	}
+put:
+	of_node_put(cur);
+	of_node_put(new);
+free:
+	kfree(mask_name);
+	kfree(map_name);
+	kfree(cells_name);
+	kfree(pass_name);
+
+	return ret;
+}
+EXPORT_SYMBOL(of_parse_phandle_with_args_map);
+
+/**
  * of_parse_phandle_with_fixed_args() - Find a node pointed by phandle in a list
  * @np:		pointer to a device tree node containing a list
  * @list_name:	property name that contains a list
diff --git a/include/linux/of.h b/include/linux/of.h
index 23bf46ee8686..92fd032b76c7 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -362,6 +362,9 @@ extern struct device_node *of_parse_phandle(const struct device_node *np,
 extern int of_parse_phandle_with_args(const struct device_node *np,
 	const char *list_name, const char *cells_name, int index,
 	struct of_phandle_args *out_args);
+extern int of_parse_phandle_with_args_map(const struct device_node *np,
+	const char *list_name, const char *stem_name, int index,
+	struct of_phandle_args *out_args);
 extern int of_parse_phandle_with_fixed_args(const struct device_node *np,
 	const char *list_name, int cells_count, int index,
 	struct of_phandle_args *out_args);
@@ -764,6 +767,15 @@ static inline int of_parse_phandle_with_args(const struct device_node *np,
 	return -ENOSYS;
 }
 
+static inline int of_parse_phandle_with_args_map(const struct device_node *np,
+						 const char *list_name,
+						 const char *stem_name,
+						 int index,
+						 struct of_phandle_args *out_args)
+{
+	return -ENOSYS;
+}
+
 static inline int of_parse_phandle_with_fixed_args(const struct device_node *np,
 	const char *list_name, int cells_count, int index,
 	struct of_phandle_args *out_args)
-- 
2.7.4

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#1709761 — [PATCH v4 3/4] of: unittest: Add phandle remapping test

Test the functionality of of_parse_phandle_with_args_map().

Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
---
 drivers/of/unittest-data/testcases.dts      |  11 +++
 drivers/of/unittest-data/tests-phandle.dtsi |  25 ++++++
 drivers/of/unittest.c                       | 120 ++++++++++++++++++++++++++++
 3 files changed, 156 insertions(+)

diff --git a/drivers/of/unittest-data/testcases.dts b/drivers/of/unittest-data/testcases.dts
index 12f7c3d649c8..173b96f39cd0 100644
--- a/drivers/of/unittest-data/testcases.dts
+++ b/drivers/of/unittest-data/testcases.dts
@@ -26,12 +26,23 @@
 / { __local_fixups__ {
 	testcase-data {
 		phandle-tests {
+			provider4 {
+				phandle-map = <0x00000008 0x00000018
+					       0x00000024 0x0000003c
+					       0x00000050 0x00000064>;
+			};
 			consumer-a {
 				phandle-list = <0x00000000 0x00000008
 						0x00000018 0x00000028
 						0x00000034 0x00000038>;
 				phandle-list-bad-args = <0x00000000 0x0000000c>;
 			};
+			consumer-b {
+				phandle-list = <0x00000000 0x00000008
+						0x00000018 0x00000024
+						0x00000030 0x00000034>;
+				phandle-list-bad-args = <0x00000000 0x0000000c>;
+			};
 		};
 		interrupts {
 			intmap0 {
diff --git a/drivers/of/unittest-data/tests-phandle.dtsi b/drivers/of/unittest-data/tests-phandle.dtsi
index 5b1527e8a7fb..59e297f497d1 100644
--- a/drivers/of/unittest-data/tests-phandle.dtsi
+++ b/drivers/of/unittest-data/tests-phandle.dtsi
@@ -25,6 +25,18 @@
 				#phandle-cells = <3>;
 			};
 
+			provider4: provider4 {
+				#phandle-cells = <2>;
+				phandle-map = <0 1 &provider1 3>,
+					      <4 0 &provider0>,
+					      <16 5 &provider3 3 5 0>,
+					      <200 8 &provider2 23 6>,
+					      <19 0 &provider2 15 0>,
+					      <2 3 &provider3 2 5 3>;
+				phandle-map-mask = <0xff 0xf>;
+				phandle-map-pass-thru = <0x0 0xf0>;
+			};
+
 			consumer-a {
 				phandle-list =	<&provider1 1>,
 						<&provider2 2 0>,
@@ -43,6 +55,19 @@
 				unterminated-string = [40 41 42 43];
 				unterminated-string-list = "first", "second", [40 41 42 43];
 			};
+
+			consumer-b {
+				phandle-list =	<&provider1 1>,
+						<&provider4 2 3>,
+						<0>,
+						<&provider4 4 0x100>,
+						<&provider4 0 0x61>,
+						<&provider0>,
+						<&provider4 19 0x20>;
+				phandle-list-bad-phandle = <12345678 0 0>;
+				phandle-list-bad-args = <&provider2 1 0>,
+							<&provider4 0>;
+			};
 		};
 	};
 };
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index 0107fc680335..c6091d1e55de 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -443,6 +443,125 @@ static void __init of_unittest_parse_phandle_with_args(void)
 	unittest(rc == -EINVAL, "expected:%i got:%i\n", -EINVAL, rc);
 }
 
+static void __init of_unittest_parse_phandle_with_args_map(void)
+{
+	struct device_node *np, *p0, *p1, *p2, *p3;
+	struct of_phandle_args args;
+	int i, rc;
+
+	np = of_find_node_by_path("/testcase-data/phandle-tests/consumer-b");
+	if (!np) {
+		pr_err("missing testcase data\n");
+		return;
+	}
+
+	p0 = of_find_node_by_path("/testcase-data/phandle-tests/provider0");
+	if (!p0) {
+		pr_err("missing testcase data\n");
+		return;
+	}
+
+	p1 = of_find_node_by_path("/testcase-data/phandle-tests/provider1");
+	if (!p1) {
+		pr_err("missing testcase data\n");
+		return;
+	}
+
+	p2 = of_find_node_by_path("/testcase-data/phandle-tests/provider2");
+	if (!p2) {
+		pr_err("missing testcase data\n");
+		return;
+	}
+
+	p3 = of_find_node_by_path("/testcase-data/phandle-tests/provider3");
+	if (!p3) {
+		pr_err("missing testcase data\n");
+		return;
+	}
+
+	rc = of_count_phandle_with_args(np, "phandle-list", "#phandle-cells");
+	unittest(rc == 7, "of_count_phandle_with_args() returned %i, expected 7\n", rc);
+
+	for (i = 0; i < 8; i++) {
+		bool passed = true;
+
+		rc = of_parse_phandle_with_args_map(np, "phandle-list",
+						    "phandle", i, &args);
+
+		/* Test the values from tests-phandle.dtsi */
+		switch (i) {
+		case 0:
+			passed &= !rc;
+			passed &= (args.np == p1);
+			passed &= (args.args_count == 1);
+			passed &= (args.args[0] == 1);
+			break;
+		case 1:
+			passed &= !rc;
+			passed &= (args.np == p3);
+			passed &= (args.args_count == 3);
+			passed &= (args.args[0] == 2);
+			passed &= (args.args[1] == 5);
+			passed &= (args.args[2] == 3);
+			break;
+		case 2:
+			passed &= (rc == -ENOENT);
+			break;
+		case 3:
+			passed &= !rc;
+			passed &= (args.np == p0);
+			passed &= (args.args_count == 0);
+			break;
+		case 4:
+			passed &= !rc;
+			passed &= (args.np == p1);
+			passed &= (args.args_count == 1);
+			passed &= (args.args[0] == 3);
+			break;
+		case 5:
+			passed &= !rc;
+			passed &= (args.np == p0);
+			passed &= (args.args_count == 0);
+			break;
+		case 6:
+			passed &= !rc;
+			passed &= (args.np == p2);
+			passed &= (args.args_count == 2);
+			passed &= (args.args[0] == 15);
+			passed &= (args.args[1] == 0x20);
+			break;
+		case 7:
+			passed &= (rc == -ENOENT);
+			break;
+		default:
+			passed = false;
+		}
+
+		unittest(passed, "index %i - data error on node %s rc=%i\n",
+			 i, args.np->full_name, rc);
+	}
+
+	/* Check for missing list property */
+	rc = of_parse_phandle_with_args_map(np, "phandle-list-missing",
+					    "phandle", 0, &args);
+	unittest(rc == -ENOENT, "expected:%i got:%i\n", -ENOENT, rc);
+
+	/* Check for missing cells,map,mask property */
+	rc = of_parse_phandle_with_args_map(np, "phandle-list",
+					    "phandle-missing", 0, &args);
+	unittest(rc == -EINVAL, "expected:%i got:%i\n", -EINVAL, rc);
+
+	/* Check for bad phandle in list */
+	rc = of_parse_phandle_with_args_map(np, "phandle-list-bad-phandle",
+					    "phandle", 0, &args);
+	unittest(rc == -EINVAL, "expected:%i got:%i\n", -EINVAL, rc);
+
+	/* Check for incorrectly formed argument list */
+	rc = of_parse_phandle_with_args_map(np, "phandle-list-bad-args",
+					    "phandle", 1, &args);
+	unittest(rc == -EINVAL, "expected:%i got:%i\n", -EINVAL, rc);
+}
+
 static void __init of_unittest_property_string(void)
 {
 	const char *strings[4];
@@ -2326,6 +2445,7 @@ static int __init of_unittest(void)
 	of_unittest_find_node_by_name();
 	of_unittest_dynamic();
 	of_unittest_parse_phandle_with_args();
+	of_unittest_parse_phandle_with_args_map();
 	of_unittest_printf();
 	of_unittest_property_string();
 	of_unittest_property_copy();
-- 
2.7.4

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#1709763 — [PATCH v4 4/4] gpio: Support gpio nexus dt bindings

Platforms like 96boards have a standardized connector/expansion
slot that exposes signals like GPIOs to expansion boards in an
SoC agnostic way. We'd like the DT overlays for the expansion
boards to be written once without knowledge of the SoC on the
other side of the connector. This avoids the unscalable
combinatorial explosion of a different DT overlay for each
expansion board and SoC pair.

Now that we have nexus support in the OF core let's change the
function call here that parses the phandle lists of gpios to use
the nexus variant. This allows us to remap phandles and their
arguments through any number of nexus nodes and end up with the
actual gpio provider being used.

Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
---
 drivers/gpio/gpiolib-of.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
index 54ce8dc58ad0..0d968c758129 100644
--- a/drivers/gpio/gpiolib-of.c
+++ b/drivers/gpio/gpiolib-of.c
@@ -75,8 +75,8 @@ struct gpio_desc *of_get_named_gpiod_flags(struct device_node *np,
 	struct gpio_desc *desc;
 	int ret;
 
-	ret = of_parse_phandle_with_args(np, propname, "#gpio-cells", index,
-					 &gpiospec);
+	ret = of_parse_phandle_with_args_map(np, propname, "gpio", index,
+					     &gpiospec);
 	if (ret) {
 		pr_debug("%s: can't parse '%s' property of node '%s[%d]'\n",
 			__func__, propname, np->full_name, index);
-- 
2.7.4

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#1712472

On Fri, Aug 11, 2017 at 10:42 AM, Stephen Boyd <stephen.boyd@linaro.org> wrote:
> This is a continutation of my phandle remapping/nexus node series
> from a while ago. I finally got around to writing the documentation
> in the spec for this, but it's really rough around the edges and
> could use some review/suggestions to get it into shape. Please
> review!
>
> This is one small chunk of work related to DT overlays for expansion
> boards. It would be good to have a way to expose #<list>-cells types of
> providers through a connector in a standard way. So we introduce a way
> to make "nexus" nodes for these types of properties to remap the consumer
> number space to the other side of the connector's number space. It's
> basically a copy of the interrupt nexus implementation, but without
> the address space matching design and interrupt-parent walking.

This generally looks good to me. I'm inclined to merge the kernel
parts now and sort the spec addition out afterwards. With no users
yet, we can still tweak things if needed.

I would like to see more comments on this though. Perhaps "OF phandle
nexus" is too obscure. Maybe "Add DT overlay connector bindings" would
trick some people in looking at it...

Rob

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