ze': drivers/usb/gadget/fsl_mxc_udc.c:98: error: implicit declaration of function 'readl' drivers/usb/gadget/fsl_mxc_udc.c:100: error: implicit declaration of function 'writel' This error is caused by the follwing commit: (16fcb63: arm/imx: remove mx31_setup_weimcs( ) from mx31.h) ,which removed '#include ' from mx31.h. fsl_mxc_udc.c includes , which in turns includes mx31.h, so that's the reason fsl_mxc_udc.c built fine previously. Instead of relying on the indirect inclusion of the linux/io.h header file, include it directly in fsl_mxc_udc.c. Signed-off-by: Fabio Estevam Signed-off-by: Felipe Balbi Signed-off-by: Greg Kroah-Hartman ²