of: Overlay manager

From e14eb45fa5a93c1bff8a6dfe7b6756e4ad72c579 Mon Sep 17 00:00:00 2001
From: Dmitry Shmidt <[email protected]>
Date: Wed, 24 Aug 2016 13:25:52 -0700
Subject: [PATCH] of: Overlay manager

Overlay manager processes DT entries on demand. It is chosen by CONFIG_OF_OVERLAY_MGR option. These entries can be chosen from kernel command line:
overlay_mgr.overlay_dt_entry=hardware_cfg_0 DT contains main overlay_mng entry with all possible HW config setups. And then kernel command line option will allow to choose between them.

  Kernel DT entry:
    overlay_mgr {
        compatible = "linux,overlay_manager";
        hardware_cfg_0 {
            overlay@0 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };

            overlay@1 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };
        };
    };

Signed-off-by Dmitry Shmidt <[email protected]>

Tested-by John Stultz <[email protected]>

Acked-by John Stultz <[email protected]>

---
 .../devicetree/bindings/of/overlay_mgr.txt         | 32 ++++++++
 drivers/of/Kconfig                                 | 10 +++
 drivers/of/Makefile                                |  1 +
 drivers/of/overlay_mgr.c                           | 90 ++++++++++++++++++++++
 4 files changed, 133 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/of/overlay_mgr.txt
 create mode 100644 drivers/of/overlay_mgr.c

Documentation/devicetree/bindings/of/overlay_mgr.txt new file +32 -0

new file mode 100644
index 0000000..5f3ce4c
@@ -0,0 +1,32 @@
+overlay_mgr
+
+Required properties:
+- compatible: "linux,overlay_manager";
+
+Optional properties:
+- starts from the word "hardware": hardware_cfg_0
+
+These properties can be chosen from kernel command line:
+overlay_mgr.overlay_dt_entry=hardware_cfg_0
+DT contains main overlay_mng entry with all possible
+HW config setups. And then kernel command line option
+will allow to choose between them.
+
+Example:
+    overlay_mgr {
+        compatible = "linux,overlay_manager";
+        hardware_cfg_0 {
+            overlay@0 {
+                    fragment@0 {
+                            __overlay__ {
+                            };
+                    };
+            };
+            overlay@1 {
+                    fragment@0 {
+                            __overlay__ {
+                            };
+                    };
+            };
+        };
+    };

drivers/of/Kconfig +10 -0

index e2a4841..e3eb06d 100644
@@ -112,4 +112,14 @@ config OF_OVERLAY
       While this option is selected automatically when needed, you can
       enable it manually to improve device tree unit test coverage.
 
+config OF_OVERLAY_MGR
+    bool "Enable Overlay manager"
+    default n
+    depends on OF_OVERLAY
+    help
+      Enables Overlay manager - it accepts DT entry from command line
+      overlay_mgr.overlay_dt_entry=<name> and applies all overlays in
+      it to current DT. It is also possible to apply predefined DT
+      entry on the fly by writing it to 'current_overlay' sysfs entry.
+
 endif # OF

drivers/of/Makefile +1 -0

index 156c072..3bddd19 100644
@@ -14,5 +14,6 @@ obj-$(CONFIG_OF_MTD)    += of_mtd.o
 obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
 obj-$(CONFIG_OF_RESOLVE)  += resolver.o
 obj-$(CONFIG_OF_OVERLAY) += overlay.o
+obj-$(CONFIG_OF_OVERLAY_MGR) += overlay_mgr.o
 
 obj-$(CONFIG_OF_UNITTEST) += unittest-data/

drivers/of/overlay_mgr.c new file +80 -0

new file mode 100644
index 0000000..1fdeb0a
@@ -0,0 +1,90 @@
+/*
+ * Overlay manager that allows to apply list of overlays from DT entry
+ *
+ * Copyright (C) 2016 Google, Inc.
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+static char *of_overlay_dt_entry;
+module_param_named(overlay_dt_entry, of_overlay_dt_entry, charp, 0644);
+
+static int of_overlay_mgr_apply_overlay(struct device_node *onp)
+{
+    int ret;
+
+    ret = of_overlay_create(onp);
+    if (ret < 0) {
+        pr_err("overlay_mgr: fail to create overlay: %d\n", ret);
+        of_node_put(onp);
+        return ret;
+    }
+    pr_info("overlay_mgr: %s overlay applied\n", onp->name);
+    return 0;
+}
+
+static int of_overlay_mgr_apply_dt(struct device *dev, char *dt_entry)
+{
+    struct device_node *enp = dev->of_node;
+    struct device_node *next;
+    struct device_node *prev = NULL;
+
+    if (!enp) {
+        pr_err("overlay_mgr: no dt entry\n");
+        return -ENODEV;
+    }
+
+    enp = of_get_child_by_name(enp, dt_entry);
+    if (!enp) {
+        pr_err("overlay_mgr: dt entry %s not found\n", dt_entry);
+        return -ENODEV;
+    }
+    pr_info("overlay_mgr: apply %s dt entry\n", enp->name);
+    while ((next = of_get_next_available_child(enp, prev)) != NULL) {
+        if (strncmp(next->name, "overlay", 7) == 0)
+            of_overlay_mgr_apply_overlay(next);
+        prev = next;
+    }
+    return 0;
+}
+
+static int of_overlay_mgr_probe(struct platform_device *pdev)
+{
+    if (!of_overlay_dt_entry)
+        return 0;
+    of_overlay_mgr_apply_dt(&pdev->dev, of_overlay_dt_entry);
+    return 0;
+}
+
+static const struct of_device_id of_overlay_mgr_match[] = {
+    { .compatible = "linux,overlay_manager", },
+    {}
+};
+
+static struct platform_driver of_overlay_mgr_driver = {
+    .probe    = of_overlay_mgr_probe,
+    .driver    = {
+        .name = "overlay_manager",

Quoted 23 lines · On 09/08/16 13:35, [email protected] wrote:

From e14eb45fa5a93c1bff8a6dfe7b6756e4ad72c579 Mon Sep 17 00:00:00 2001
From: Dmitry Shmidt <[email protected]>
Date: Wed, 24 Aug 2016 13:25:52 -0700
Subject: [PATCH] of: Overlay manager

Overlay manager processes DT entries on demand. It is chosen by CONFIG_OF_OVERLAY_MGR option. These entries can be chosen from kernel command line:
overlay_mgr.overlay_dt_entry=hardware_cfg_0 DT contains main overlay_mng entry with all possible HW config setups. And then kernel command line option will allow to choose between them.

  Kernel DT entry:
    overlay_mgr {
        compatible = "linux,overlay_manager";
        hardware_cfg_0 {
            overlay@0 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };

Quoted 8 lines

            overlay@1 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };
        };
    };

What problem(s) are you trying to solve with this?

What is the use case?

-Frank

Quoted 177 lines

Signed-off-by Dmitry Shmidt <[email protected]>

Tested-by John Stultz <[email protected]>

Acked-by John Stultz <[email protected]>

---
 .../devicetree/bindings/of/overlay_mgr.txt         | 32 ++++++++
 drivers/of/Kconfig                                 | 10 +++
 drivers/of/Makefile                                |  1 +
 drivers/of/overlay_mgr.c                           | 90 ++++++++++++++++++++++
 4 files changed, 133 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/of/overlay_mgr.txt
 create mode 100644 drivers/of/overlay_mgr.c

Documentation/devicetree/bindings/of/overlay_mgr.txt new file +32 -0

new file mode 100644
index 0000000..5f3ce4c
@@ -0,0 +1,32 @@
+overlay_mgr
+
+Required properties:
+- compatible: "linux,overlay_manager";
+
+Optional properties:
+- starts from the word "hardware": hardware_cfg_0
+
+These properties can be chosen from kernel command line:
+overlay_mgr.overlay_dt_entry=hardware_cfg_0
+DT contains main overlay_mng entry with all possible
+HW config setups. And then kernel command line option
+will allow to choose between them.
+
+Example:
+    overlay_mgr {
+        compatible = "linux,overlay_manager";
+        hardware_cfg_0 {
+            overlay@0 {
+                    fragment@0 {
+                            __overlay__ {
+                            };
+                    };
+            };
+            overlay@1 {
+                    fragment@0 {
+                            __overlay__ {
+                            };
+                    };
+            };
+        };
+    };

drivers/of/Kconfig +10 -0

index e2a4841..e3eb06d 100644
@@ -112,4 +112,14 @@ config OF_OVERLAY
       While this option is selected automatically when needed, you can
       enable it manually to improve device tree unit test coverage.
 
+config OF_OVERLAY_MGR
+    bool "Enable Overlay manager"
+    default n
+    depends on OF_OVERLAY
+    help
+      Enables Overlay manager - it accepts DT entry from command line
+      overlay_mgr.overlay_dt_entry=<name> and applies all overlays in
+      it to current DT. It is also possible to apply predefined DT
+      entry on the fly by writing it to 'current_overlay' sysfs entry.
+
 endif # OF

drivers/of/Makefile +1 -0

index 156c072..3bddd19 100644
@@ -14,5 +14,6 @@ obj-$(CONFIG_OF_MTD)    += of_mtd.o
 obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
 obj-$(CONFIG_OF_RESOLVE)  += resolver.o
 obj-$(CONFIG_OF_OVERLAY) += overlay.o
+obj-$(CONFIG_OF_OVERLAY_MGR) += overlay_mgr.o
 
 obj-$(CONFIG_OF_UNITTEST) += unittest-data/

drivers/of/overlay_mgr.c new file +90 -0

new file mode 100644
index 0000000..1fdeb0a
@@ -0,0 +1,90 @@
+/*
+ * Overlay manager that allows to apply list of overlays from DT entry
+ *
+ * Copyright (C) 2016 Google, Inc.
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+static char *of_overlay_dt_entry;
+module_param_named(overlay_dt_entry, of_overlay_dt_entry, charp, 0644);
+
+static int of_overlay_mgr_apply_overlay(struct device_node *onp)
+{
+    int ret;
+
+    ret = of_overlay_create(onp);
+    if (ret < 0) {
+        pr_err("overlay_mgr: fail to create overlay: %d\n", ret);
+        of_node_put(onp);
+        return ret;
+    }
+    pr_info("overlay_mgr: %s overlay applied\n", onp->name);
+    return 0;
+}
+
+static int of_overlay_mgr_apply_dt(struct device *dev, char *dt_entry)
+{
+    struct device_node *enp = dev->of_node;
+    struct device_node *next;
+    struct device_node *prev = NULL;
+
+    if (!enp) {
+        pr_err("overlay_mgr: no dt entry\n");
+        return -ENODEV;
+    }
+
+    enp = of_get_child_by_name(enp, dt_entry);
+    if (!enp) {
+        pr_err("overlay_mgr: dt entry %s not found\n", dt_entry);
+        return -ENODEV;
+    }
+    pr_info("overlay_mgr: apply %s dt entry\n", enp->name);
+    while ((next = of_get_next_available_child(enp, prev)) != NULL) {
+        if (strncmp(next->name, "overlay", 7) == 0)
+            of_overlay_mgr_apply_overlay(next);
+        prev = next;
+    }
+    return 0;
+}
+
+static int of_overlay_mgr_probe(struct platform_device *pdev)
+{
+    if (!of_overlay_dt_entry)
+        return 0;
+    of_overlay_mgr_apply_dt(&pdev->dev, of_overlay_dt_entry);
+    return 0;
+}
+
+static const struct of_device_id of_overlay_mgr_match[] = {
+    { .compatible = "linux,overlay_manager", },
+    {}
+};
+
+static struct platform_driver of_overlay_mgr_driver = {
+    .probe    = of_overlay_mgr_probe,
+    .driver    = {
+        .name = "overlay_manager",
+        .of_match_table = of_match_ptr(of_overlay_mgr_match),
+    },
+};
+
+static int __init of_overlay_mgr_init(void)
+{
+    return platform_driver_register(&of_overlay_mgr_driver);
+}
+
+postcore_initcall(of_overlay_mgr_init);

Quoted 33 lines · Frank Rowand

Quoted 23 lines · On 09/08/16 13:35, [email protected] wrote:

From e14eb45fa5a93c1bff8a6dfe7b6756e4ad72c579 Mon Sep 17 00:00:00 2001
From: Dmitry Shmidt <[email protected]>
Date: Wed, 24 Aug 2016 13:25:52 -0700
Subject: [PATCH] of: Overlay manager

Overlay manager processes DT entries on demand. It is chosen by CONFIG_OF_OVERLAY_MGR option. These entries can be chosen from kernel command line:
overlay_mgr.overlay_dt_entry=hardware_cfg_0 DT contains main overlay_mng entry with all possible HW config setups. And then kernel command line option will allow to choose between them.

  Kernel DT entry:
    overlay_mgr {
        compatible = "linux,overlay_manager";
        hardware_cfg_0 {
            overlay@0 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };

Quoted 8 lines

            overlay@1 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };
        };
    };

Quoted 1 line

What problem(s) are you trying to solve with this?

Currently the Linux kernel doesn't provide a way for boot time selection of different possible board configurations, when the board peripherals are specified via Device Tree.

Thus, this patch provides a driver which takes a boot option to apply pre-defined device-tree overlay fragments on bootup. This allows a single kernel/devicetree to be able to support a number of different configurations by only changing a boot argument.

Quoted 1 line

What is the use case?

It is usually useful for development board when you can use different peripherals. For example you want to use special LCD panel. Using it will go on account of other stuff like GPIOs, so you don't want it all the time. And it is not convenient to apply new patches and to recompile the kernel. And this code allows to choose LCD panel configuration from command line.

Quoted 45 lines · Dmitry Shmidt

Quoted 33 lines · Frank Rowand

Quoted 23 lines · On 09/08/16 13:35, [email protected] wrote:

From e14eb45fa5a93c1bff8a6dfe7b6756e4ad72c579 Mon Sep 17 00:00:00 2001
From: Dmitry Shmidt <[email protected]>
Date: Wed, 24 Aug 2016 13:25:52 -0700
Subject: [PATCH] of: Overlay manager

Overlay manager processes DT entries on demand. It is chosen by CONFIG_OF_OVERLAY_MGR option. These entries can be chosen from kernel command line:
overlay_mgr.overlay_dt_entry=hardware_cfg_0 DT contains main overlay_mng entry with all possible HW config setups. And then kernel command line option will allow to choose between them.

  Kernel DT entry:
    overlay_mgr {
        compatible = "linux,overlay_manager";
        hardware_cfg_0 {
            overlay@0 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };

Quoted 8 lines

            overlay@1 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };
        };
    };

Quoted 1 line

What problem(s) are you trying to solve with this?

Currently the Linux kernel doesn't provide a way for boot time selection of different possible board configurations, when the board peripherals are specified via Device Tree.

Thus, this patch provides a driver which takes a boot option to apply pre-defined device-tree overlay fragments on bootup. This allows a single kernel/devicetree to be able to support a number of different configurations by only changing a boot argument.

Quoted 8 lines

Quoted 1 line

What is the use case?

It is usually useful for development board when you can use different peripherals. For example you want to use special LCD panel. Using it will go on account of other stuff like GPIOs, so you don't want it all the time. And it is not convenient to apply new patches and to recompile the kernel. And this code allows to choose LCD panel configuration from command line.

In other words, you want to be able to make configuration choices at boot time.

The hardware is not different between boots, but you may want to use it in different ways, with a boot time selection.

Quoted 6 lines · Frank Rowand

Quoted 5 lines · On 09/08/16 13:35, [email protected] wrote:

From e14eb45fa5a93c1bff8a6dfe7b6756e4ad72c579 Mon Sep 17 00:00:00 2001
From: Dmitry Shmidt <[email protected]>
Date: Wed, 24 Aug 2016 13:25:52 -0700
Subject: [PATCH] of: Overlay manager

Quoted 7 lines

Quoted 7 lines

Overlay manager processes DT entries on demand. It is chosen by CONFIG_OF_OVERLAY_MGR option. These entries can be chosen from kernel command line:
overlay_mgr.overlay_dt_entry=hardware_cfg_0 DT contains main overlay_mng entry with all possible HW config setups. And then kernel command line option will allow to choose between them.

Quoted 4 lines

Quoted 4 lines

  Kernel DT entry:
    overlay_mgr {
        compatible = "linux,overlay_manager";

Quoted 1 line

Quoted 1 line

        hardware_cfg_0 {

Quoted 15 lines

Quoted 14 lines

            overlay@0 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };
            overlay@1 {
                    fragment@0 {
                            __overlay__ {
                            };
                    };
            };
        };
    };

Quoted 1 line

What problem(s) are you trying to solve with this?

Currently the Linux kernel doesn't provide a way for boot time selection of different possible board configurations, when the board peripherals are specified via Device Tree.

Thus, this patch provides a driver which takes a boot option to apply pre-defined device-tree overlay fragments on bootup. This allows a single kernel/devicetree to be able to support a number of different configurations by only changing a boot argument.

Quoted 1 line

What is the use case?

It is usually useful for development board when you can use different peripherals. For example you want to use special LCD panel. Using it will go on account of other stuff like GPIOs, so you don't want it all the time. And it is not convenient to apply new patches and to recompile the kernel. And this code allows to choose LCD panel configuration from command line.

Quoted 6 lines · Dmitry Shmidt

Quoted 1 line · Frank Rowand

What problem(s) are you trying to solve with this?

Currently the Linux kernel doesn't provide a way for boot time selection of different possible board configurations, when the board peripherals are specified via Device Tree.

Well, the kernel does provide a way. For different h/w you give it a different h/w description (i.e. dtb). The issue is having multiple dtbs for mostly similar h/w is a PIA.

Also, it can be argued this should remain a bootloader problem. For the LCD case, the bootloader is going to need that information to support a splash screen. libfdt is learning how to apply overlays on flat trees.

Quoted 8 lines

Quoted 1 line

What is the use case?

It is usually useful for development board when you can use different peripherals. For example you want to use special LCD panel. Using it will go on account of other stuff like GPIOs, so you don't want it all the time. And it is not convenient to apply new patches and to recompile the kernel. And this code allows to choose LCD panel configuration from command line.

If you can figure out how to change the command line, then you can just change the dtb. At least for how Android boot works, those aren't really changed separately.

Quoted 11 lines · Rob Herring

Quoted 6 lines · Dmitry Shmidt

Quoted 1 line · Frank Rowand

What problem(s) are you trying to solve with this?

Currently the Linux kernel doesn't provide a way for boot time selection of different possible board configurations, when the board peripherals are specified via Device Tree.

Well, the kernel does provide a way. For different h/w you give it a different h/w description (i.e. dtb). The issue is having multiple dtbs for mostly similar h/w is a PIA.

Agreed.

Quoted 4 lines

Also, it can be argued this should remain a bootloader problem. For the LCD case, the bootloader is going to need that information to support a splash screen. libfdt is learning how to apply overlays on flat trees.

I can imagine in many cases like devboards with various attached shields/mezzanines the bootloader doesn't (and likely can't) have this ability.

Quoted 9 lines

Quoted 8 lines

Quoted 1 line

What is the use case?

It is usually useful for development board when you can use different peripherals. For example you want to use special LCD panel. Using it will go on account of other stuff like GPIOs, so you don't want it all the time. And it is not convenient to apply new patches and to recompile the kernel. And this code allows to choose LCD panel configuration from command line.

Quoted 3 lines

If you can figure out how to change the command line, then you can just change the dtb. At least for how Android boot works, those aren't really changed separately.

Ehh.. that's not so simple. The dtb is often appended to the kernel on Android devices. Changing the boot arguments is much simpler to do.

Quoted 7 lines · John Stultz

Quoted 3 lines · Rob Herring

If you can figure out how to change the command line, then you can just change the dtb. At least for how Android boot works, those aren't really changed separately.

Ehh.. that's not so simple. The dtb is often appended to the kernel on Android devices. Changing the boot arguments is much simpler to do.

How? You typically make a new bootimage assembling the kernel/dtb, ramdisk and kernel command-line. If things were done differently such that the dtb is part of the bootloader (how it is supposed to be done), then I would buy the argument that we can't update the dtb and need to either have a way to add and/or select overlays. But Android folks like to update *everything*, so I don't buy that here.

Quoted 9 lines · Rob Herring

Quoted 7 lines · John Stultz

Quoted 3 lines · Rob Herring

If you can figure out how to change the command line, then you can just change the dtb. At least for how Android boot works, those aren't really changed separately.

Ehh.. that's not so simple. The dtb is often appended to the kernel on Android devices. Changing the boot arguments is much simpler to do.

Quoted 6 lines

How? You typically make a new bootimage assembling the kernel/dtb, ramdisk and kernel command-line. If things were done differently such that the dtb is part of the bootloader (how it is supposed to be done), then I would buy the argument that we can't update the dtb and need to either have a way to add and/or select overlays. But Android folks like to update *everything*, so I don't buy that here.

So in many cases the dtb is appended when the kernel is built, not when the abootimg is assembled.

So its much easier to use abootimg -u to update a prebuilt boot.img in place and reflash. That way users don't need to regenerate the kernel w/ appended dtb.

thanks
-john

Quoted 9 lines · John Stultz

So in many cases the dtb is appended when the kernel is built, not when the abootimg is assembled.

So its much easier to use abootimg -u to update a prebuilt boot.img in place and reflash. That way users don't need to regenerate the kernel w/ appended dtb.

I understand what you’re trying to do, but it’s not going to work.

It will only work for a very small subset of overlays since you can’t have more than a single phandle label.

For instance this will not work:

overlays {
        overlay_0 {
                opt: opt_0 { bar; };
        };
        overlay_1 {
                opt: opt_1 { baz; };
        };
};

frob_device {
        compatible = “frob”;
        use = <&opt>;
};

If your use case is simple enough you’ll never hit this, but it does happen in more complex examples.

Hi John,

Quoted 19 lines · John Stultz

Quoted 9 lines · Rob Herring

Quoted 7 lines · John Stultz

Quoted 3 lines · Rob Herring

If you can figure out how to change the command line, then you can just change the dtb. At least for how Android boot works, those aren't really changed separately.

Ehh.. that's not so simple. The dtb is often appended to the kernel on Android devices. Changing the boot arguments is much simpler to do.

Quoted 6 lines

How? You typically make a new bootimage assembling the kernel/dtb, ramdisk and kernel command-line. If things were done differently such that the dtb is part of the bootloader (how it is supposed to be done), then I would buy the argument that we can't update the dtb and need to either have a way to add and/or select overlays. But Android folks like to update *everything*, so I don't buy that here.

Quoted 7 lines

So in many cases the dtb is appended when the kernel is built, not when the abootimg is assembled.

So its much easier to use abootimg -u to update a prebuilt boot.img in place and reflash. That way users don't need to regenerate the kernel w/ appended dtb.

I understand what you’re trying to do, but it’s not going to work.

It will only work for a very small subset of overlays since you can’t have more than a single phandle label.

For instance this will not work:

overlays {
        overlay_0 {
                opt: opt_0 { bar; };
        };
        overlay_1 {
                opt: opt_1 { baz; };
        };
};

frob_device {
        compatible = “frob”;
        use = <&opt>;
};