fdt: Add option to default to most compatible conf in a fit image

When booting a fit image with multiple configurations, the user either has to
specify which configuration to use explicitly, or there has to be a default
defined which is chosen automatically. This change adds an option to change
that behavior so that a configuration can be selected explicitly, or the
configuration which has the device tree that claims to be compatible with the
earliest item in U-Boot's device tree.

In other words, if U-Boot claimed to be compatible with A, B, and then C, and
the configurations claimed to be compatible with A, D and B, D and D, E, the
first configuration, A, D, would be chosen. Both the first and second
configurations match, but the first one matches a more specific entry in
U-Boot's device tree. The order in the kernel's device tree is ignored.

Signed-off-by: Gabe Black <gabeblack@google.com>

Commit-Ready: Gabe Black <gabeblack@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>

2 files changed, 138 insertions, 0 deletions

diff --git a/common/cmd_bootm.c b/common/cmd_bootm.c
index d256ddfaa..4dbe952bb 100644
--- a/common/cmd_bootm.c
+++ b/common/cmd_bootm.c
@@ -949,8 +949,19 @@ static void *boot_get_kernel(cmd_tbl_t *cmdtp, int flag, int argc,
 			 * node
 			 */
 			bootstage_mark(BOOTSTAGE_ID_FIT_NO_UNIT_NAME);
+#ifdef CONFIG_FIT_BEST_MATCH
+			if (fit_uname_config)
+				cfg_noffset =
+					fit_conf_get_node(fit_hdr,
+							  fit_uname_config);
+			else
+				cfg_noffset =
+					fit_conf_find_compat(fit_hdr,
+							     gd->fdt_blob);
+#else
 			cfg_noffset = fit_conf_get_node(fit_hdr,
 							fit_uname_config);
+#endif
 			if (cfg_noffset < 0) {
 				bootstage_error(BOOTSTAGE_ID_FIT_NO_UNIT_NAME);
 				return NULL;
diff --git a/common/image.c b/common/image.c
index df642e656..e93b6e89c 100644
--- a/common/image.c
+++ b/common/image.c
@@ -3049,6 +3049,133 @@ int fit_check_format(const void *fit)
 	return 1;
 }
 
+
+/**
+ * fit_conf_find_compat
+ * @fit: pointer to the FIT format image header
+ * @fdt: pointer to the device tree to compare against
+ *
+ * fit_conf_find_compat() attempts to find the configuration whose fdt is the
+ * most compatible with the passed in device tree.
+ *
+ * Example:
+ *
+ * / o image-tree
+ *   |-o images
+ *   | |-o fdt@1
+ *   | |-o fdt@2
+ *   |
+ *   |-o configurations
+ *     |-o config@1
+ *     | |-fdt = fdt@1
+ *     |
+ *     |-o config@2
+ *       |-fdt = fdt@2
+ *
+ * / o U-Boot fdt
+ *   |-compatible = "foo,bar", "bim,bam"
+ *
+ * / o kernel fdt1
+ *   |-compatible = "foo,bar",
+ *
+ * / o kernel fdt2
+ *   |-compatible = "bim,bam", "baz,biz"
+ *
+ * Configuration 1 would be picked because the first string in U-Boot's
+ * compatible list, "foo,bar", matches a compatible string in the root of fdt1.
+ * "bim,bam" in fdt2 matches the second string which isn't as good as fdt1.
+ *
+ * returns:
+ *     offset to the configuration to use if one was found
+ *     -1 otherwise
+ */
+int fit_conf_find_compat(const void *fit, const void *fdt)
+{
+	int ndepth = 0;
+	int noffset, confs_noffset, images_noffset;
+	const void *fdt_compat;
+	int fdt_compat_len;
+	int best_match_offset = 0;
+	int best_match_pos = 0;
+
+	confs_noffset = fdt_path_offset(fit, FIT_CONFS_PATH);
+	images_noffset = fdt_path_offset(fit, FIT_IMAGES_PATH);
+	if (confs_noffset < 0 || images_noffset < 0) {
+		debug("Can't find configurations or images nodes.\n");
+		return -1;
+	}
+
+	fdt_compat = fdt_getprop(fdt, 0, "compatible", &fdt_compat_len);
+	if (!fdt_compat) {
+		debug("Fdt for comparison has no \"compatible\" property.\n");
+		return -1;
+	}
+
+	/*
+	 * Loop over the configurations in the FIT image.
+	 */
+	for (noffset = fdt_next_node(fit, confs_noffset, &ndepth);
+			(noffset >= 0) && (ndepth > 0);
+			noffset = fdt_next_node(fit, noffset, &ndepth)) {
+		const void *kfdt;
+		const char *kfdt_name;
+		int kfdt_noffset;
+		const char *cur_fdt_compat;
+		int len;
+		size_t size;
+		int i;
+
+		if (ndepth > 1)
+			continue;
+
+		kfdt_name = fdt_getprop(fit, noffset, "fdt", &len);
+		if (!kfdt_name) {
+			debug("No fdt property found.\n");
+			continue;
+		}
+		kfdt_noffset = fdt_subnode_offset(fit, images_noffset,
+						  kfdt_name);
+		if (kfdt_noffset < 0) {
+			debug("No image node named \"%s\" found.\n",
+			      kfdt_name);
+			continue;
+		}
+		/*
+		 * Get a pointer to this configuration's fdt.
+		 */
+		if (fit_image_get_data(fit, kfdt_noffset, &kfdt, &size)) {
+			debug("Failed to get fdt \"%s\".\n", kfdt_name);
+			continue;
+		}
+
+		len = fdt_compat_len;
+		cur_fdt_compat = fdt_compat;
+		/*
+		 * Look for a match for each U-Boot compatibility string in
+		 * turn in this configuration's fdt.
+		 */
+		for (i = 0; len > 0 &&
+		     (!best_match_offset || best_match_pos > i); i++) {
+			int cur_len = strlen(cur_fdt_compat) + 1;
+
+			if (!fdt_node_check_compatible(kfdt, 0,
+						       cur_fdt_compat)) {
+				best_match_offset = noffset;
+				best_match_pos = i;
+				break;
+			}
+			len -= cur_len;
+			cur_fdt_compat += cur_len;
+		}
+	}
+	if (!best_match_offset) {
+		debug("No match found.\n");
+		return -1;
+	}
+
+	return best_match_offset;
+}
+
 /**
  * fit_conf_get_node - get node offset for configuration of a given unit name
  * @fit: pointer to the FIT format image header