add $sys substitution

udev.7

@@ -362,6 +362,11 @@ The node name of the parent device.
 The udev_root value.
 .RE
 .PP
+\fB$sys\fR, \fB%S\fR
+.RS 4
+The sysfs mount point.
+.RE
+.PP
 \fB$tempnode\fR, \fB%N\fR
 .RS 4
 The name of a created temporary device node to provide access to the device from a external program before the real node is created.

udev.xml

@@ -529,6 +529,13 @@
               </listitem>
             </varlistentry>
 
+            <varlistentry>
+              <term><option>$sys</option>, <option>%S</option></term>
+              <listitem>
+                <para>The sysfs mount point.</para>
+              </listitem>
+            </varlistentry>
+
             <varlistentry>
               <term><option>$tempnode</option>, <option>%N</option></term>
               <listitem>

udev_rules.c

@@ -292,6 +292,7 @@ void udev_rules_apply_format(struct udevice *udev, char *string, size_t maxsize)
 		SUBST_PARENT,
 		SUBST_TEMP_NODE,
 		SUBST_ROOT,
+		SUBST_SYS,
 		SUBST_ENV,
 	};
 	static const struct subst_map {
@@ -311,6 +312,7 @@ void udev_rules_apply_format(struct udevice *udev, char *string, size_t maxsize)
 		{ .name = "parent",	.fmt = 'P',	.type = SUBST_PARENT },
 		{ .name = "tempnode",	.fmt = 'N',	.type = SUBST_TEMP_NODE },
 		{ .name = "root",	.fmt = 'r',	.type = SUBST_ROOT },
+		{ .name = "sys",	.fmt = 'S',	.type = SUBST_SYS },
 		{ .name = "env",	.fmt = 'E',	.type = SUBST_ENV },
 		{ NULL, '\0', 0 }
 	};
@@ -516,6 +518,10 @@ found:
 			strlcat(string, udev_root, maxsize);
 			dbg("substitute udev_root '%s'", udev_root);
 			break;
+		case SUBST_SYS:
+			strlcat(string, sysfs_path, maxsize);
+			dbg("substitute sysfs_path '%s'", sysfs_path);
+			break;
 		case SUBST_ENV:
 			if (attr == NULL) {
 				dbg("missing attribute");