stand/fdt: Consolidate overlay handling a little further

This should have been done as part of r327350, but due to lack of foresight
it came later. In the different places we apply overlays, we duplicate the
bits that check for fdt_overlays in the environment and supplement that with
any other places we need to check for overlays to load. These "other places"
will be loader specific and are not candidates for consolidation.

Provide an fdt_load_dtb_overlays to capture the common logic, allow passing
in an additional list of overlays to be loaded. This additional list of
overlays is used in practice for ubldr to pull in any fdt_overlays passed to
it from U-Boot environment, but it can be used for any other source of
overlays.

These additional overlays supplement loader.conf(5) fdt_overlays, rather
than replace, so that we're not restricted to specifying overlays in only
one place. This is a change from previous behavior where loader.conf(5)
supplied fdt_overlays would cause us to ignore U-Boot environment, and this
seems nonsensical- user should have sufficient control over both of these
aspects, or lack of control for good reasons.

A knob could be considered in the future to ignore U-Boot supplied overlays,
but the supplemental treatment seems like a good start.

Reviewed by:	imp (earlier version), gonzo (earlier version)
Differential Revision:	https://reviews.freebsd.org/D13993

stand/efi/fdt/efi_fdt.c

@@ -53,12 +53,7 @@ fdt_platform_load_dtb(void)
 		return (1);
 	printf("Using DTB provided by EFI at %p.\n", hdr);
 
-	s = getenv("fdt_overlays");
-	if (s != NULL && *s != '\0') {
-		printf("Loading DTB overlays: '%s'\n", s);
-		fdt_load_dtb_overlays(s);
-	}
-
+	fdt_load_dtb_overlays(NULL);
 	return (0);
 }
 

stand/fdt/fdt_loader_cmd.c

@@ -76,6 +76,7 @@ static int fdt_load_dtb(vm_offset_t va);
 static void fdt_print_overlay_load_error(int err, const char *filename);
 
 static int fdt_cmd_nyi(int argc, char *argv[]);
+static int fdt_load_dtb_overlays_string(const char * filenames);
 
 static int fdt_cmd_addr(int argc, char *argv[]);
 static int fdt_cmd_mkprop(int argc, char *argv[]);
@@ -331,15 +332,15 @@ fdt_print_overlay_load_error(int err, const char *filename)
 	}
 }
 
-int
-fdt_load_dtb_overlays(const char * filenames)
+static int
+fdt_load_dtb_overlays_string(const char * filenames)
 {
 	char *names;
 	char *name, *name_ext;
 	char *comaptr;
 	int err, namesz;
 
-	debugf("fdt_load_dtb_overlay(%s)\n", filenames);
+	debugf("fdt_load_dtb_overlays_string(%s)\n", filenames);
 
 	names = strdup(filenames);
 	if (names == NULL)
@@ -832,6 +833,25 @@ fdt_fixup_stdout(const char *str)
 	}
 }
 
+void
+fdt_load_dtb_overlays(const char *extras)
+{
+	const char *s;
+
+	/* Any extra overlays supplied by pre-loader environment */
+	if (extras != NULL && *extras != '\0') {
+		printf("Loading DTB overlays: '%s'\n", extras);
+		fdt_load_dtb_overlays_string(extras);
+	}
+
+	/* Any overlays supplied by loader environment */
+	s = getenv("fdt_overlays");
+	if (s != NULL && *s != '\0') {
+		printf("Loading DTB overlays: '%s'\n", s);
+		fdt_load_dtb_overlays_string(s);
+	}
+}
+
 /*
  * Locate the blob, fix it up and return its location.
  */

stand/fdt/fdt_platform.h

@@ -46,7 +46,7 @@ void fdt_fixup_stdout(const char *);
 void fdt_apply_overlays(void);
 int fdt_load_dtb_addr(struct fdt_header *);
 int fdt_load_dtb_file(const char *);
-int fdt_load_dtb_overlays(const char *);
+void fdt_load_dtb_overlays(const char *);
 int fdt_setup_fdtp(void);
 
 /* The platform library needs to implement these functions */

stand/uboot/fdt/uboot_fdt.c

@@ -89,16 +89,8 @@ fdt_platform_load_dtb(void)
 	}
 
 exit:
-	if (rv == 0) {
-		s = getenv("fdt_overlays");
-		if (s == NULL)
-			s = ub_env_get("fdt_overlays");
-		if (s != NULL && *s != '\0') {
-			printf("Loading DTB overlays: '%s'\n", s);
-			fdt_load_dtb_overlays(s);
-		}
-	}
-
+	if (rv == 0)
+		fdt_load_dtb_overlays(ub_env_get("fdt_overlays"));
 	return (rv);
 }