Here is the patch I used to fix build error.

diff --git a/drivers/usb.c b/drivers/usb.c
index 0da6efa..a959389 100644
--- a/drivers/usb.c
+++ b/drivers/usb.c
@@ -20,7 +20,7 @@
#include <libpayload-config.h>

/* Only use this code if libpayload is compiled with USB stack */
-#ifdef CONFIG_USB
+#ifdef CONFIG_USB_DISK
#include <fs.h>
#include <usb/usb.h>
#include <usb/usbmsc.h>

Please let me know if this is correct and I should submit it

On Fri, Oct 10, 2014 at 11:41 PM, Vipin Gahlaut <gailu96@gmail.com> wrote:

Hi,

We need USB support in Filo. Our Linux kernel and file system is expected to be on USB thumb driver. We have enabled USB in menuconfig; however build fails with following errors.

blockdev.c:(.text+0x18e): undefined reference to `usb_read'
/home/vgahlaut/coreboot-fsp/coreboot/payloads/filo/build/fs/blockdev.o: In function `devopen':
blockdev.c:(.text+0x91e): undefined reference to `usb_probe'

We are using latest FILO and Coreboot from git repository. These functions seems to be defined in drivers/usb.c and usb.c is getting compiled.

Problem seems to be due to the fact that CONFIG_USB=y in .config is automatically removed during make and these function are defined in usb.c under #ifdef CONFIG_USB

Can you please suggest a solution and let me know why CONFIG_USB is removed from my .config