[PATCH v2 1/2] environment: support DT-compatible-specific overlays

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

From: Ahmad Fatoum <a.fatoum@barebox.org>

Board-specific environments are registered from board code via
defaultenv_append_directory(), but this isn't possible when using
CONFIG_DEFAULT_ENVIRONMENT_PATH with an external environment.

Add support for a match.of_compatible/ directory convention within
the default environment. Subdirectories named after DT root compatible
strings are overlaid onto /env from most generic to most specific
after the default environment is loaded. The match.of_compatible/
directory is removed afterwards to keep /env clean.

Example layout in CONFIG_DEFAULT_ENVIRONMENT_PATH:

  barebox-defaultenv/
    nv/boot.default
    match.of_compatible/
      fsl,imx8mm/
        nv/boot.default
      fsl,imx8mm-evk/
        nv/boot.default

For compatible = "fsl,imx8mm-evk", "fsl,imx8mm":
  1. fsl,imx8mm/     overlay applied first  (most generic)
  2. fsl,imx8mm-evk/ overlay applied second (most specific)

Signed-off-by: Ahmad Fatoum <a.fatoum@barebox.org>
---
v1 -> v2:
  - Fix typo in commit message (Marco)
  - Add documentation for the feature (Marco)
---
 Documentation/user/defaultenv-2.rst | 29 ++++++++++++++++++
 common/startup.c                    | 47 +++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/Documentation/user/defaultenv-2.rst b/Documentation/user/defaultenv-2.rst
index e5cb4a51bfad..2564eb959fcc 100644
--- a/Documentation/user/defaultenv-2.rst
+++ b/Documentation/user/defaultenv-2.rst
@@ -155,3 +155,32 @@ This contains the files to be sourced when barebox detects that the OS
 had requested a specific :ref:`reboot_mode` (via e.g. ``reboot bootloader``
 under Linux). After the ``/env/init`` scripts were executed, barebox will
 ``source /env/bmode/${global.system.reboot_mode.prev}`` if available.
+
+/env/mach.of_compatible/
+------------------------
+
+On devicetree enabled systems, this optional directory may contain
+environment overlays that should be applied onto ``/env``.
+
+Each subdirectory should be named after a device tree root compatible
+string and they will be applied from most generic to most specific match
+after the default environment is loaded.
+The ``match.of_compatible/`` directory is removed afterwards to keep
+``/env`` clean.
+
+For example, given ``CONFIG_DEFAULT_ENVIRONMENT_PATH`` pointing
+at an external ``barebox-defaultenv/`` directory::
+
+  barebox-defaultenv/
+    nv/boot.default     -> kernel-common
+    match.of_compatible/
+      fsl,imx8mm/
+        nv/boot.default -> kernel-mx8mm
+      fsl,imx8mm-evk/
+        nv/boot.default -> kernel-mx8mm-evk
+
+The final ``/env/nv/boot.default`` would be:
+
+- For ``compatible = "fsl,imx8mm-evk", "fsl,imx8mm";``,  ``kernel-mx8mm-evk``
+- For ``compatible = "fsl,imx8mm-evkb", "fsl,imx8mm";``, ``kernel-mx8mm``
+- For ``compatible = "fsl,imx8mp-evk", "fsl,imx8mp";``,  ``kernel-common``
diff --git a/common/startup.c b/common/startup.c
index 2e2b5f820fe9..e630033e3505 100644
--- a/common/startup.c
+++ b/common/startup.c
@@ -46,6 +46,7 @@
 #include <pbl/handoff-data.h>
 #include <libfile.h>
 #include <fuzz.h>
+#include <of.h>
 
 extern initcall_t __barebox_initcalls_start[], __barebox_early_initcalls_end[],
 		  __barebox_initcalls_end[];
@@ -95,6 +96,50 @@ void autoload_external_env(bool endis)
 }
 #endif
 
+static void env_merge_of_compat_overlays(const char *dir)
+{
+	struct device_node *root;
+	const char *compat;
+	struct stat s;
+	char *ofdir, *src;
+	int count;
+
+	root = of_get_root_node();
+	if (!root)
+		return;
+
+	ofdir = xasprintf("%s/match.of_compatible", dir);
+
+	if (stat(ofdir, &s) || !S_ISDIR(s.st_mode))
+		goto out;
+
+	count = of_property_count_strings(root, "compatible");
+
+	/*
+	 * Apply overlays from most generic to most specific, so that
+	 * more specific entries take precedence.
+	 */
+	for (int i = count - 1; i >= 0; i--) {
+		if (of_property_read_string_index(root, "compatible",
+						  i, &compat))
+			continue;
+
+		src = xasprintf("%s/%s", ofdir, compat);
+
+		if (stat(src, &s) == 0 && S_ISDIR(s.st_mode)) {
+			pr_debug("Applying '%s'-compatible environment overlay\n",
+				 compat);
+			copy_recursive(src, dir, 0);
+		}
+
+		free(src);
+	}
+
+	unlink_recursive(ofdir, NULL);
+out:
+	free(ofdir);
+}
+
 static int load_environment(void)
 {
 	const char *default_environment_path;
@@ -115,6 +160,8 @@ static int load_environment(void)
 		pr_info("external environment support %s. Using default environment\n",
 			IS_ENABLED(CONFIG_ENV_HANDLING) ? "disallowed" : "disabled");
 
+	env_merge_of_compat_overlays("/env");
+
 	nvvar_load();
 
 	return 0;
-- 
2.47.3