1 files changed, 88 insertions, 0 deletions

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 23ffb7c0caf2..ad8ac1a8af28 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -385,3 +385,91 @@ struct device_node *of_find_matching_node(struct device_node *from,
         return np;
 }
 EXPORT_SYMBOL(of_find_matching_node);
+
+/**
+ * of_modalias_table: Table of explicit compatible ==> modalias mappings
+ *
+ * This table allows particulare compatible property values to be mapped
+ * to modalias strings.  This is useful for busses which do not directly
+ * understand the OF device tree but are populated based on data contained
+ * within the device tree.  SPI and I2C are the two current users of this
+ * table.
+ *
+ * In most cases, devices do not need to be listed in this table because
+ * the modalias value can be derived directly from the compatible table.
+ * However, if for any reason a value cannot be derived, then this table
+ * provides a method to override the implicit derivation.
+ *
+ * At the moment, a single table is used for all bus types because it is
+ * assumed that the data size is small and that the compatible values
+ * should already be distinct enough to differentiate between SPI, I2C
+ * and other devices.
+ */
+struct of_modalias_table {
+        char *of_device;
+        char *modalias;
+};
+static struct of_modalias_table of_modalias_table[] = {
+        /* Empty for now; add entries as needed */
+};
+
+/**
+ * of_modalias_node - Lookup appropriate modalias for a device node
+ * @node:       pointer to a device tree node
+ * @modalias:   Pointer to buffer that modalias value will be copied into
+ * @len:        Length of modalias value
+ *
+ * Based on the value of the compatible property, this routine will determine
+ * an appropriate modalias value for a particular device tree node.  Three
+ * separate methods are used to derive a modalias value.
+ *
+ * First method is to lookup the compatible value in of_modalias_table.
+ * Second is to look for a "linux,<modalias>" entry in the compatible list
+ * and used that for modalias.  Third is to strip off the manufacturer
+ * prefix from the first compatible entry and use the remainder as modalias
+ *
+ * This routine returns 0 on success
+ */
+int of_modalias_node(struct device_node *node, char *modalias, int len)
+{
+        int i, cplen;
+        const char *compatible;
+        const char *p;
+
+        /* 1. search for exception list entry */
+        for (i = 0; i < ARRAY_SIZE(of_modalias_table); i++) {
+                compatible = of_modalias_table[i].of_device;
+                if (!of_device_is_compatible(node, compatible))
+                        continue;
+                strlcpy(modalias, of_modalias_table[i].modalias, len);
+                return 0;
+        }
+
+        compatible = of_get_property(node, "compatible", &cplen);
+        if (!compatible)
+                return -ENODEV;
+
+        /* 2. search for linux,<modalias> entry */
+        p = compatible;
+        while (cplen > 0) {
+                if (!strncmp(p, "linux,", 6)) {
+                        p += 6;
+                        strlcpy(modalias, p, len);
+                        return 0;
+                }
+
+                i = strlen(p) + 1;
+                p += i;
+                cplen -= i;
+        }
+
+        /* 3. take first compatible entry and strip manufacturer */
+        p = strchr(compatible, ',');
+        if (!p)
+                return -ENODEV;
+        p++;
+        strlcpy(modalias, p, len);
+        return 0;
+}
+EXPORT_SYMBOL_GPL(of_modalias_node);
+