[PATCH v2 1/8] qcom: board: validate fdt before trying to use it

[Volodymyr Babchuk]

There are cases when previous bootloader stage leaves some seemingly
valid value in r0, which in fact does not point to valid FDT
blob. This behavior was encountered when trying to boot U-Boot as
"hyp" loader on SA8155P-ADP.

To be sure that we really got the pointer to a device tree we need to
validate it with fdt_valid() function.

Note: This approach is not 100% fool-proof, as get_prev_bl_fdt_addr()
theoretically can return a pointer to a region that is not physically
mapped and we will get data abort exception when "fdt_valid" will try
to access it. But at this early boot stage we don't know where RAM is
anyways so there is little we can do.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk at epam.com>

---

Changes in v2:
 - New patch in v2

 arch/arm/mach-snapdragon/board.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-snapdragon/board.c b/arch/arm/mach-snapdragon/board.c
index f12f5791a1..10eec47ada 100644
--- a/arch/arm/mach-snapdragon/board.c
+++ b/arch/arm/mach-snapdragon/board.c
@@ -24,6 +24,7 @@
 #include <linux/sizes.h>
 #include <lmb.h>
 #include <malloc.h>
+#include <fdt_support.h>
 #include <usb.h>
 #include <sort.h>
 
@@ -93,7 +94,9 @@ void *board_fdt_blob_setup(int *err)
 	 * try and use the FDT built into U-Boot if there is one...
 	 * This avoids having a hard dependency on the previous stage bootloader
 	 */
-	if (IS_ENABLED(CONFIG_OF_SEPARATE) && (!fdt || fdt != ALIGN(fdt, SZ_4K))) {
+
+	if (IS_ENABLED(CONFIG_OF_SEPARATE) && (!fdt || fdt != ALIGN(fdt, SZ_4K) ||
+					       !fdt_valid((void *)&fdt))) {
 		debug("%s: Using built in FDT, bootloader gave us %#llx\n", __func__, fdt);
 		return (void *)gd->fdt_blob;
 	}
-- 
2.43.0