Allow overlay device tree file system, remove dtc that does not work with overlays

4 files changed, 720 insertions, 4 deletions

diff --git a/recipes-kernel/linux/linux-at91-4.9/950-0090-OF-DT-Overlay-configfs-interface.patch b/recipes-kernel/linux/linux-at91-4.9/950-0090-OF-DT-Overlay-configfs-interface.patch
new file mode 100644
index 0000000..6a0d9ee
--- /dev/null
+++ b/recipes-kernel/linux/linux-at91-4.9/950-0090-OF-DT-Overlay-configfs-interface.patch
@@ -0,0 +1,427 @@
+This patch comes from:
+https://git.telliq.com/gtu/openwrt/blob/e34ea1b4ff6db504718258cbcc40bdbd730e57a3/target/linux/brcm2708/patches-4.9/950-0090-OF-DT-Overlay-configfs-interface.patch
+
+From ef4a8376af32bb6722e1ea933a9e1a83ebc8f175 Mon Sep 17 00:00:00 2001
+From: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
+Date: Wed, 3 Dec 2014 13:23:28 +0200
+Subject: [PATCH] OF: DT-Overlay configfs interface
+
+This is a port of Pantelis Antoniou's v3 port that makes use of the
+new upstreamed configfs support for binary attributes.
+
+Original commit message:
+
+Add a runtime interface to using configfs for generic device tree overlay
+usage. With it its possible to use device tree overlays without having
+to use a per-platform overlay manager.
+
+Please see Documentation/devicetree/configfs-overlays.txt for more info.
+
+Changes since v2:
+- Removed ifdef CONFIG_OF_OVERLAY (since for now it's required)
+- Created a documentation entry
+- Slight rewording in Kconfig
+
+Changes since v1:
+- of_resolve() -> of_resolve_phandles().
+
+Originally-signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
+Signed-off-by: Phil Elwell <phil@raspberrypi.org>
+
+DT configfs: Fix build errors on other platforms
+
+Signed-off-by: Phil Elwell <phil@raspberrypi.org>
+
+DT configfs: fix build error
+
+There is an error when compiling rpi-4.6.y branch:
+  CC      drivers/of/configfs.o
+drivers/of/configfs.c:291:21: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
+   .default_groups = of_cfs_def_groups,
+                     ^
+drivers/of/configfs.c:291:21: note: (near initialization for 'of_cfs_subsys.su_group.default_groups.next')
+
+The .default_groups is linked list since commit
+1ae1602de028acaa42a0f6ff18d19756f8e825c6.
+This commit uses configfs_add_default_group to fix this problem.
+
+Signed-off-by: Slawomir Stepien <sst@poczta.fm>
+---
+ Documentation/devicetree/configfs-overlays.txt |  31 +++
+ drivers/of/Kconfig                             |   7 +
+ drivers/of/Makefile                            |   1 +
+ drivers/of/configfs.c                          | 311 +++++++++++++++++++++++++
+ 4 files changed, 350 insertions(+)
+ create mode 100644 Documentation/devicetree/configfs-overlays.txt
+ create mode 100644 drivers/of/configfs.c
+
+--- /dev/null
++++ b/Documentation/devicetree/configfs-overlays.txt
+@@ -0,0 +1,31 @@
++Howto use the configfs overlay interface.
++
++A device-tree configfs entry is created in /config/device-tree/overlays
++and and it is manipulated using standard file system I/O.
++Note that this is a debug level interface, for use by developers and
++not necessarily something accessed by normal users due to the
++security implications of having direct access to the kernel's device tree.
++
++* To create an overlay you mkdir the directory:
++
++	# mkdir /config/device-tree/overlays/foo
++
++* Either you echo the overlay firmware file to the path property file.
++
++	# echo foo.dtbo >/config/device-tree/overlays/foo/path
++
++* Or you cat the contents of the overlay to the dtbo file
++
++	# cat foo.dtbo >/config/device-tree/overlays/foo/dtbo
++
++The overlay file will be applied, and devices will be created/destroyed
++as required.
++
++To remove it simply rmdir the directory.
++
++	# rmdir /config/device-tree/overlays/foo
++
++The rationalle of the dual interface (firmware & direct copy) is that each is
++better suited to different use patterns. The firmware interface is what's
++intended to be used by hardware managers in the kernel, while the copy interface
++make sense for developers (since it avoids problems with namespaces).
+--- a/drivers/of/Kconfig
++++ b/drivers/of/Kconfig
+@@ -112,4 +112,11 @@ config OF_OVERLAY
+ config OF_NUMA
+ 	bool
+ 
++config OF_CONFIGFS
++	bool "Device Tree Overlay ConfigFS interface"
++	select CONFIGFS_FS
++	select OF_OVERLAY
++	help
++	  Enable a simple user-space driven DT overlay interface.
++
+ endif # OF
+--- a/drivers/of/Makefile
++++ b/drivers/of/Makefile
+@@ -1,4 +1,5 @@
+ obj-y = base.o device.o platform.o
++obj-$(CONFIG_OF_CONFIGFS) += configfs.o
+ obj-$(CONFIG_OF_DYNAMIC) += dynamic.o
+ obj-$(CONFIG_OF_FLATTREE) += fdt.o
+ obj-$(CONFIG_OF_EARLY_FLATTREE) += fdt_address.o
+--- /dev/null
++++ b/drivers/of/configfs.c
+@@ -0,0 +1,311 @@
++/*
++ * Configfs entries for device-tree
++ *
++ * Copyright (C) 2013 - Pantelis Antoniou <panto@antoniou-consulting.com>
++ *
++ * This program is free software; you can redistribute it and/or
++ * modify it under the terms of the GNU General Public License
++ * as published by the Free Software Foundation; either version
++ * 2 of the License, or (at your option) any later version.
++ */
++#include <linux/ctype.h>
++#include <linux/cpu.h>
++#include <linux/module.h>
++#include <linux/of.h>
++#include <linux/of_fdt.h>
++#include <linux/spinlock.h>
++#include <linux/slab.h>
++#include <linux/proc_fs.h>
++#include <linux/configfs.h>
++#include <linux/types.h>
++#include <linux/stat.h>
++#include <linux/limits.h>
++#include <linux/file.h>
++#include <linux/vmalloc.h>
++#include <linux/firmware.h>
++#include <linux/sizes.h>
++
++#include "of_private.h"
++
++struct cfs_overlay_item {
++	struct config_item	item;
++
++	char			path[PATH_MAX];
++
++	const struct firmware	*fw;
++	struct device_node	*overlay;
++	int			ov_id;
++
++	void			*dtbo;
++	int			dtbo_size;
++};
++
++static int create_overlay(struct cfs_overlay_item *overlay, void *blob)
++{
++	int err;
++
++	/* unflatten the tree */
++	of_fdt_unflatten_tree(blob, NULL, &overlay->overlay);
++	if (overlay->overlay == NULL) {
++		pr_err("%s: failed to unflatten tree\n", __func__);
++		err = -EINVAL;
++		goto out_err;
++	}
++	pr_debug("%s: unflattened OK\n", __func__);
++
++	/* mark it as detached */
++	of_node_set_flag(overlay->overlay, OF_DETACHED);
++
++	/* perform resolution */
++	err = of_resolve_phandles(overlay->overlay);
++	if (err != 0) {
++		pr_err("%s: Failed to resolve tree\n", __func__);
++		goto out_err;
++	}
++	pr_debug("%s: resolved OK\n", __func__);
++
++	err = of_overlay_create(overlay->overlay);
++	if (err < 0) {
++		pr_err("%s: Failed to create overlay (err=%d)\n",
++				__func__, err);
++		goto out_err;
++	}
++	overlay->ov_id = err;
++
++out_err:
++	return err;
++}
++
++static inline struct cfs_overlay_item *to_cfs_overlay_item(
++		struct config_item *item)
++{
++	return item ? container_of(item, struct cfs_overlay_item, item) : NULL;
++}
++
++static ssize_t cfs_overlay_item_path_show(struct config_item *item,
++		char *page)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++	return sprintf(page, "%s\n", overlay->path);
++}
++
++static ssize_t cfs_overlay_item_path_store(struct config_item *item,
++		const char *page, size_t count)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++	const char *p = page;
++	char *s;
++	int err;
++
++	/* if it's set do not allow changes */
++	if (overlay->path[0] != '\0' || overlay->dtbo_size > 0)
++		return -EPERM;
++
++	/* copy to path buffer (and make sure it's always zero terminated */
++	count = snprintf(overlay->path, sizeof(overlay->path) - 1, "%s", p);
++	overlay->path[sizeof(overlay->path) - 1] = '\0';
++
++	/* strip trailing newlines */
++	s = overlay->path + strlen(overlay->path);
++	while (s > overlay->path && *--s == '\n')
++		*s = '\0';
++
++	pr_debug("%s: path is '%s'\n", __func__, overlay->path);
++
++	err = request_firmware(&overlay->fw, overlay->path, NULL);
++	if (err != 0)
++		goto out_err;
++
++	err = create_overlay(overlay, (void *)overlay->fw->data);
++	if (err != 0)
++		goto out_err;
++
++	return count;
++
++out_err:
++
++	release_firmware(overlay->fw);
++	overlay->fw = NULL;
++
++	overlay->path[0] = '\0';
++	return err;
++}
++
++static ssize_t cfs_overlay_item_status_show(struct config_item *item,
++		char *page)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++
++	return sprintf(page, "%s\n",
++			overlay->ov_id >= 0 ? "applied" : "unapplied");
++}
++
++CONFIGFS_ATTR(cfs_overlay_item_, path);
++CONFIGFS_ATTR_RO(cfs_overlay_item_, status);
++
++static struct configfs_attribute *cfs_overlay_attrs[] = {
++	&cfs_overlay_item_attr_path,
++	&cfs_overlay_item_attr_status,
++	NULL,
++};
++
++ssize_t cfs_overlay_item_dtbo_read(struct config_item *item,
++		void *buf, size_t max_count)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++
++	pr_debug("%s: buf=%p max_count=%zu\n", __func__,
++			buf, max_count);
++
++	if (overlay->dtbo == NULL)
++		return 0;
++
++	/* copy if buffer provided */
++	if (buf != NULL) {
++		/* the buffer must be large enough */
++		if (overlay->dtbo_size > max_count)
++			return -ENOSPC;
++
++		memcpy(buf, overlay->dtbo, overlay->dtbo_size);
++	}
++
++	return overlay->dtbo_size;
++}
++
++ssize_t cfs_overlay_item_dtbo_write(struct config_item *item,
++		const void *buf, size_t count)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++	int err;
++
++	/* if it's set do not allow changes */
++	if (overlay->path[0] != '\0' || overlay->dtbo_size > 0)
++		return -EPERM;
++
++	/* copy the contents */
++	overlay->dtbo = kmemdup(buf, count, GFP_KERNEL);
++	if (overlay->dtbo == NULL)
++		return -ENOMEM;
++
++	overlay->dtbo_size = count;
++
++	err = create_overlay(overlay, overlay->dtbo);
++	if (err != 0)
++		goto out_err;
++
++	return count;
++
++out_err:
++	kfree(overlay->dtbo);
++	overlay->dtbo = NULL;
++	overlay->dtbo_size = 0;
++
++	return err;
++}
++
++CONFIGFS_BIN_ATTR(cfs_overlay_item_, dtbo, NULL, SZ_1M);
++
++static struct configfs_bin_attribute *cfs_overlay_bin_attrs[] = {
++	&cfs_overlay_item_attr_dtbo,
++	NULL,
++};
++
++static void cfs_overlay_release(struct config_item *item)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++
++	if (overlay->ov_id >= 0)
++		of_overlay_destroy(overlay->ov_id);
++	if (overlay->fw)
++		release_firmware(overlay->fw);
++	/* kfree with NULL is safe */
++	kfree(overlay->dtbo);
++	kfree(overlay);
++}
++
++static struct configfs_item_operations cfs_overlay_item_ops = {
++	.release	= cfs_overlay_release,
++};
++
++static struct config_item_type cfs_overlay_type = {
++	.ct_item_ops	= &cfs_overlay_item_ops,
++	.ct_attrs	= cfs_overlay_attrs,
++	.ct_bin_attrs	= cfs_overlay_bin_attrs,
++	.ct_owner	= THIS_MODULE,
++};
++
++static struct config_item *cfs_overlay_group_make_item(
++		struct config_group *group, const char *name)
++{
++	struct cfs_overlay_item *overlay;
++
++	overlay = kzalloc(sizeof(*overlay), GFP_KERNEL);
++	if (!overlay)
++		return ERR_PTR(-ENOMEM);
++	overlay->ov_id = -1;
++
++	config_item_init_type_name(&overlay->item, name, &cfs_overlay_type);
++	return &overlay->item;
++}
++
++static void cfs_overlay_group_drop_item(struct config_group *group,
++		struct config_item *item)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++
++	config_item_put(&overlay->item);
++}
++
++static struct configfs_group_operations overlays_ops = {
++	.make_item	= cfs_overlay_group_make_item,
++	.drop_item	= cfs_overlay_group_drop_item,
++};
++
++static struct config_item_type overlays_type = {
++	.ct_group_ops   = &overlays_ops,
++	.ct_owner       = THIS_MODULE,
++};
++
++static struct configfs_group_operations of_cfs_ops = {
++	/* empty - we don't allow anything to be created */
++};
++
++static struct config_item_type of_cfs_type = {
++	.ct_group_ops   = &of_cfs_ops,
++	.ct_owner       = THIS_MODULE,
++};
++
++struct config_group of_cfs_overlay_group;
++
++static struct configfs_subsystem of_cfs_subsys = {
++	.su_group = {
++		.cg_item = {
++			.ci_namebuf = "device-tree",
++			.ci_type = &of_cfs_type,
++		},
++	},
++	.su_mutex = __MUTEX_INITIALIZER(of_cfs_subsys.su_mutex),
++};
++
++static int __init of_cfs_init(void)
++{
++	int ret;
++
++	pr_info("%s\n", __func__);
++
++	config_group_init(&of_cfs_subsys.su_group);
++	config_group_init_type_name(&of_cfs_overlay_group, "overlays",
++			&overlays_type);
++	configfs_add_default_group(&of_cfs_overlay_group,
++			&of_cfs_subsys.su_group);
++
++	ret = configfs_register_subsystem(&of_cfs_subsys);
++	if (ret != 0) {
++		pr_err("%s: failed to register subsys\n", __func__);
++		goto out;
++	}
++	pr_info("%s: OK\n", __func__);
++out:
++	return ret;
++}
++late_initcall(of_cfs_init);
diff --git a/recipes-kernel/linux/linux-at91-4.9/mtcdt/defconfig b/recipes-kernel/linux/linux-at91-4.9/mtcdt/defconfig
index d08d412..bf26f84 100644
--- a/recipes-kernel/linux/linux-at91-4.9/mtcdt/defconfig
+++ b/recipes-kernel/linux/linux-at91-4.9/mtcdt/defconfig
@@ -875,6 +875,7 @@ CONFIG_OF_MDIO=y
 CONFIG_OF_RESERVED_MEM=y
 CONFIG_OF_RESOLVE=y
 CONFIG_OF_OVERLAY=y
+CONFIG_OF_CONFIGFS=y
 CONFIG_ARCH_MIGHT_HAVE_PC_PARPORT=y
 # CONFIG_PARPORT is not set
 CONFIG_BLK_DEV=y
@@ -3015,7 +3016,7 @@ CONFIG_FANOTIFY=y
 # CONFIG_QUOTACTL is not set
 # CONFIG_AUTOFS4_FS is not set
 # CONFIG_FUSE_FS is not set
-# CONFIG_OVERLAY_FS is not set
+CONFIG_OVERLAY_FS=y
 
 #
 # Caches
diff --git a/recipes-kernel/linux/linux-at91-4.9/v5-3-9-OF-DT-Overlay-configfs-interface.diff b/recipes-kernel/linux/linux-at91-4.9/v5-3-9-OF-DT-Overlay-configfs-interface.diff
new file mode 100644
index 0000000..619b888
--- /dev/null
+++ b/recipes-kernel/linux/linux-at91-4.9/v5-3-9-OF-DT-Overlay-configfs-interface.diff
@@ -0,0 +1,287 @@
+Patch from:
+https://lore.kernel.org/patchwork/patch/468129/
+
+This patch will not compile with the 4.9.87 kernel.
+
+ConfigFS overlay
+==================================================================================
+diff -aNru linux-4.9.87.orig/drivers/of/Kconfig linux-4.9.87/drivers/of/Kconfig
+--- linux-4.9.87.orig/drivers/of/Kconfig	2018-12-05 10:47:45.348494186 -0600
++++ linux-4.9.87/drivers/of/Kconfig	2018-12-05 11:05:10.272463251 -0600
+@@ -112,4 +112,11 @@
+ config OF_NUMA
+ 	bool
+
++config OF_CONFIGFS
++	bool "OpenFirmware Overlay ConfigFS interface"
++	select CONFIGFS_FS
++	select OF_OVERLAY
++	help
++	  Enable a simple user-space driver DT overlay interface.
++
+ endif # OF
+diff -aNru linux-4.9.87.orig/drivers/of/Makefile linux-4.9.87/drivers/of/Makefile
+--- linux-4.9.87.orig/drivers/of/Makefile	2018-12-05 10:48:27.836492928 -0600
++++ linux-4.9.87/drivers/of/Makefile	2018-12-05 11:05:57.668461848 -0600
+@@ -14,5 +14,6 @@
+ obj-$(CONFIG_OF_RESOLVE)  += resolver.o
+ obj-$(CONFIG_OF_OVERLAY) += overlay.o
+ obj-$(CONFIG_OF_NUMA) += of_numa.o
++obj-$(CONFIG_OF_CONFIGFS) += configfs.o
+ 
+ obj-$(CONFIG_OF_UNITTEST) += unittest-data/
+diff -aNru linux-4.9.87.orig/drivers/of/configfs.c linux-4.9.87/drivers/of/configfs.c
+--- linux-4.9.87.orig/drivers/of/configfs.c	1969-12-31 18:00:00.000000000 -0600
++++ linux-4.9.87/drivers/of/configfs.c	2018-12-05 10:58:59.056474241 -0600
+@@ -0,0 +1,251 @@
++/*
++ * Configfs entries for device-tree
++ *
++ * Copyright (C) 2013 - Pantelis Antoniou <panto@antoniou-consulting.com>
++ *
++ * This program is free software; you can redistribute it and/or
++ * modify it under the terms of the GNU General Public License
++ * as published by the Free Software Foundation; either version
++ * 2 of the License, or (at your option) any later version.
++ */
++#include <linux/ctype.h>
++#include <linux/cpu.h>
++#include <linux/module.h>
++#include <linux/of.h>
++#include <linux/of_fdt.h>
++#include <linux/spinlock.h>
++#include <linux/slab.h>
++#include <linux/proc_fs.h>
++#include <linux/configfs.h>
++#include <linux/types.h>
++#include <linux/stat.h>
++#include <linux/limits.h>
++#include <linux/file.h>
++#include <linux/vmalloc.h>
++#include <linux/firmware.h>
++
++#include "of_private.h"
++
++#ifdef CONFIG_OF_OVERLAY
++
++struct cfs_overlay_item {
++	struct config_item	item;
++
++	char			path[PATH_MAX];
++
++	const struct firmware	*fw;
++	struct device_node	*overlay;
++	int			ov_id;
++};
++
++static inline struct cfs_overlay_item *to_cfs_overlay_item(
++		struct config_item *item)
++{
++	return item ? container_of(item, struct cfs_overlay_item, item) : NULL;
++}
++
++CONFIGFS_ATTR_STRUCT(cfs_overlay_item);
++#define CFS_OVERLAY_ITEM_ATTR(_name, _mode, _show, _store)	\
++struct cfs_overlay_item_attribute cfs_overlay_item_attr_##_name = \
++	__CONFIGFS_ATTR(_name, _mode, _show, _store)
++#define CFS_OVERLAY_ITEM_ATTR_RO(_name, _show)	\
++struct cfs_overlay_item_attribute cfs_overlay_item_attr_##_name = \
++	__CONFIGFS_ATTR_RO(_name, _show)
++
++static ssize_t cfs_overlay_item_path_show(struct cfs_overlay_item *overlay,
++		char *page)
++{
++	return sprintf(page, "%s\n", overlay->path);
++}
++
++static ssize_t cfs_overlay_item_path_store(struct cfs_overlay_item *overlay,
++		const char *page, size_t count)
++{
++	const char *p = page;
++	char *s;
++	int err;
++
++	/* if it's set do not allow changes */
++	if (overlay->path[0] != '\0')
++		return -EPERM;
++
++	/* copy to path buffer (and make sure it's always zero terminated */
++	count = snprintf(overlay->path, sizeof(overlay->path) - 1, "%s", p);
++	overlay->path[sizeof(overlay->path) - 1] = '\0';
++
++	/* strip trailing newlines */
++	s = overlay->path + strlen(overlay->path);
++	while (s > overlay->path && *--s == '\n')
++		*s = '\0';
++
++	pr_debug("%s: path is '%s'\n", __func__, overlay->path);
++
++	err = request_firmware(&overlay->fw, overlay->path, NULL);
++	if (err != 0)
++		goto out_err;
++
++	/* unflatten the tree */
++	of_fdt_unflatten_tree((void *)overlay->fw->data, &overlay->overlay);
++	if (overlay->overlay == NULL) {
++		pr_err("%s: failed to unflatten tree\n", __func__);
++		err = -EINVAL;
++		goto out_err;
++	}
++	pr_debug("%s: unflattened OK\n", __func__);
++
++	/* mark it as detached */
++	of_node_set_flag(overlay->overlay, OF_DETACHED);
++
++	/* perform resolution */
++	err = of_resolve(overlay->overlay);
++	if (err != 0) {
++		pr_err("%s: Failed to resolve tree\n", __func__);
++		goto out_err;
++	}
++	pr_debug("%s: resolved OK\n", __func__);
++
++	err = of_overlay_create(overlay->overlay);
++	if (err < 0) {
++		pr_err("%s: Failed to create overlay (err=%d)\n",
++				__func__, err);
++		goto out_err;
++	}
++	overlay->ov_id = err;
++
++	return count;
++
++out_err:
++
++	release_firmware(overlay->fw);
++	overlay->fw = NULL;
++
++	overlay->path[0] = '\0';
++	return err;
++}
++
++static ssize_t cfs_overlay_item_status_show(struct cfs_overlay_item *overlay,
++		char *page)
++{
++	return sprintf(page, "%s\n",
++			overlay->ov_id >= 0 ? "applied" : "unapplied");
++}
++
++CFS_OVERLAY_ITEM_ATTR(path, S_IRUGO | S_IWUSR,
++		cfs_overlay_item_path_show, cfs_overlay_item_path_store);
++CFS_OVERLAY_ITEM_ATTR_RO(status, cfs_overlay_item_status_show);
++
++static struct configfs_attribute *cfs_overlay_attrs[] = {
++	&cfs_overlay_item_attr_path.attr,
++	&cfs_overlay_item_attr_status.attr,
++	NULL,
++};
++
++static void cfs_overlay_release(struct config_item *item)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++
++	if (overlay->ov_id >= 0)
++		of_overlay_destroy(overlay->ov_id);
++	if (overlay->fw)
++		release_firmware(overlay->fw);
++	kfree(overlay);
++}
++
++CONFIGFS_ATTR_OPS(cfs_overlay_item);
++static struct configfs_item_operations cfs_overlay_item_ops = {
++	.release		= cfs_overlay_release,
++	.show_attribute		= cfs_overlay_item_attr_show,
++	.store_attribute	= cfs_overlay_item_attr_store,
++};
++
++static struct config_item_type cfs_overlay_type = {
++	.ct_item_ops	= &cfs_overlay_item_ops,
++	.ct_attrs	= cfs_overlay_attrs,
++	.ct_owner	= THIS_MODULE,
++};
++
++static struct config_item *cfs_overlay_group_make_item(
++		struct config_group *group, const char *name)
++{
++	struct cfs_overlay_item *overlay;
++
++	overlay = kzalloc(sizeof(*overlay), GFP_KERNEL);
++	if (!overlay)
++		return ERR_PTR(-ENOMEM);
++	overlay->ov_id = -1;
++
++	config_item_init_type_name(&overlay->item, name, &cfs_overlay_type);
++	return &overlay->item;
++}
++
++static void cfs_overlay_group_drop_item(struct config_group *group,
++		struct config_item *item)
++{
++	struct cfs_overlay_item *overlay = to_cfs_overlay_item(item);
++
++	config_item_put(&overlay->item);
++}
++
++static struct configfs_group_operations overlays_ops = {
++	.make_item	= cfs_overlay_group_make_item,
++	.drop_item	= cfs_overlay_group_drop_item,
++};
++
++static struct config_item_type overlays_type = {
++	.ct_group_ops   = &overlays_ops,
++	.ct_owner       = THIS_MODULE,
++};
++
++#endif /* CONFIG_OF_OVERLAY */
++
++static struct configfs_group_operations of_cfs_ops = {
++	/* empty - we don't allow anything to be created */
++};
++
++static struct config_item_type of_cfs_type = {
++	.ct_group_ops   = &of_cfs_ops,
++	.ct_owner       = THIS_MODULE,
++};
++
++struct config_group of_cfs_overlay_group;
++
++struct config_group *of_cfs_def_groups[] = {
++#ifdef CONFIG_OF_OVERLAY
++	&of_cfs_overlay_group,
++#endif
++	NULL
++};
++
++static struct configfs_subsystem of_cfs_subsys = {
++	.su_group = {
++		.cg_item = {
++			.ci_namebuf = "device-tree",
++			.ci_type = &of_cfs_type,
++		},
++		.default_groups = of_cfs_def_groups,
++	},
++	.su_mutex = __MUTEX_INITIALIZER(of_cfs_subsys.su_mutex),
++};
++
++static int __init of_cfs_init(void)
++{
++	int ret;
++
++	pr_info("%s\n", __func__);
++
++	config_group_init(&of_cfs_subsys.su_group);
++#ifdef CONFIG_OF_OVERLAY
++	config_group_init_type_name(&of_cfs_overlay_group, "overlays",
++			&overlays_type);
++#endif
++
++	ret = configfs_register_subsystem(&of_cfs_subsys);
++	if (ret != 0) {
++		pr_err("%s: failed to register subsys\n", __func__);
++		goto out;
++	}
++	pr_info("%s: OK\n", __func__);
++out:
++	return ret;
++}
++late_initcall(of_cfs_init);
diff --git a/recipes-kernel/linux/linux-at91_4.9.bb b/recipes-kernel/linux/linux-at91_4.9.bb
index 28d6a14..10e9152 100644
--- a/recipes-kernel/linux/linux-at91_4.9.bb
+++ b/recipes-kernel/linux/linux-at91_4.9.bb
@@ -30,6 +30,7 @@ SRC_URI_append_mtcdt = "\
             file://defconfig \
             file://linux-4.9-mtcdt-device-tree.patch \
             file://linux-4.9-add-num_accessory_ports-config-option.patch \
+            file://950-0090-OF-DT-Overlay-configfs-interface.patch \
             "
 
 DTB_APPEND_mtcdt = "mtcdt"
@@ -101,10 +102,10 @@ pkg_postinst_kernel-image-uimage-inst() {
 	fi
 }
 
-# Install dtc and fixdep to build any device tree overlays in other recipes/modules.
+# The 4.9 kernel dtc will not work with overlays, so don't install dtc and fixdep
 do_install_append() {
-	install -D -m 0755 scripts/dtc/dtc ${STAGING_DIR_NATIVE}${USRBINPATH_class-native}/dtc
-	install -D -m 0755 scripts/basic/fixdep ${STAGING_DIR_NATIVE}${USRBINPATH_class-native}/fixdep
+	#install -D -m 0755 scripts/dtc/dtc ${STAGING_DIR_NATIVE}${USRBINPATH_class-native}/dtc
+	#install -D -m 0755 scripts/basic/fixdep ${STAGING_DIR_NATIVE}${USRBINPATH_class-native}/fixdep
         install -d -m 0755  ${D}${includedir}/linux
         cp -a ${STAGING_KERNEL_DIR}/include/dt-bindings ${D}${includedir}/linux/
         install -d -m 0755 ${STAGING_DIR_TARGET}/${includedir}/linux