implicit declaration of function 這種警告問題的原因及解決方法

最近在改進SD卡的SEP4020驅動時，在改掉所有的warning時老報一個implicit declaration of function 的警告錯誤，上網查了下原因，原來有兩種情況會産生這種情況

1  沒有把函數所在的c檔案生成.o目标檔案

2  在函數所在的c檔案中定義了，但是沒有在與之相關聯的.h檔案中聲明

[[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的頭部将 <linux/clk.h>包含進去就行了

這樣就沒有任何warning産生了，呵呵