implicit declaration of function 这种警告问题的原因及解决方法

最近在改进SD卡的SEP4020驱动时，在改掉所有的warning时老报一个implicit declaration of function 的警告错误，上网查了下原因，原来有两种情况会产生这种情况

1  没有把函数所在的c文件生成.o目标文件

2  在函数所在的c文件中定义了，但是没有在与之相关联的.h文件中声明

[[email protected] linux]# make

  CHK     include/linux/version.h

make[1]: “include/asm-arm/mach-types.h”是最新的。

  CHK     include/linux/compile.h

  CHK     usr/initramfs_list

  CC      drivers/mmc/sep_mci.o

drivers/mmc/sep_mci.c: In function `sep4020sdi_probe':

drivers/mmc/sep_mci.c:745: warning: implicit declaration of function `clk_get'

drivers/mmc/sep_mci.c:745: warning: assignment makes pointer from integer without a cast

drivers/mmc/sep_mci.c:754: warning: implicit declaration of function `clk_enable'

drivers/mmc/sep_mci.c:800: warning: implicit declaration of function `clk_put'

drivers/mmc/sep_mci.c: In function `sep4020sdi_remove':

drivers/mmc/sep_mci.c:830: warning: implicit declaration of function `clk_disable'

drivers/mmc/sep_mci.c: In function `sep4020sdi_irq':

drivers/mmc/sep_mci.c:197: warning: 'sdi_cclear' might be used uninitialized in this function

drivers/mmc/sep_mci.c: In function `sep4020sdi_probe':

drivers/mmc/sep_mci.c:673: warning: 'host' might be used uninitialized in this function

drivers/mmc/sep_mci.c: At top level:

drivers/mmc/sep_mci.c:337: warning: 'sep4020sdi_irq_cd' defined but not used

  LD      drivers/mmc/built-in.o

  LD      drivers/built-in.o

  GEN     .version

  CHK     include/linux/compile.h

  UPD     include/linux/compile.h

  CC      init/version.o

  LD      init/built-in.o

  LD      .tmp_vmlinux1

  KSYM    .tmp_kallsyms1.S

  AS      .tmp_kallsyms1.o

  LD      .tmp_vmlinux2

  KSYM    .tmp_kallsyms2.S

  AS      .tmp_kallsyms2.o

  LD      vmlinux

  SYSMAP  System.map

  SYSMAP  .tmp_System.map

  OBJCOPY arch/arm/boot/Image

  Kernel: arch/arm/boot/Image is ready

  GZIP    arch/arm/boot/compressed/piggy.gz

  AS      arch/arm/boot/compressed/piggy.o

  LD      arch/arm/boot/compressed/vmlinux

  OBJCOPY arch/arm/boot/zImage

  Kernel: arch/arm/boot/zImage is ready

  Building modules, stage 2.

  MODPOST

于是我在sep_mci.c的头部将 <linux/clk.h>包含进去就行了

这样就没有任何warning产生了，呵呵