I am new to the Linux Kernel programming, and still learning the OS concepts. (but project deadlines don’t consider it u know ;-)
Can anyone explain why do we write driver code like this :
static void s3c24a0_ac97_write(struct ac97_codec *codec, u8 reg, u16 val){
down(&CAR_mutex); //ACQUIRE SEMAPHORE //
init_completion(&CAR_completion); //MAKE CODE ATOMIC //
AC_CODEC_CMD = AC_CMD_ADDR(reg) | AC_CMD_DATA(val); //CRITICAL SECTION //
wait_for_completion(&CAR_completion);
up(&CAR_mutex); //RELEASE SEAMPHORE //
}
why it cant be written as
static void s3c24a0_ac97_write(struct ac97_codec *codec, u8 reg, u16 val)
{
AC_CODEC_CMD = AC_CMD_ADDR(reg) | AC_CMD_DATA(val);
}
what is the meaning of down,up,completion etc.
see the commnets embedded above hope that helps you are trying to change the value of a variable which may be read or write by any other process so acquiring it using a semaphore and then after completing the opn.. releasing semaphore .
Someone Please correct me if i am wrong ?
Shiv Kumar Garg
Senior Software Engineer
System LSI Division
Samsung India Software Operation
3/1 Millers Road, Bangalore
Phone: +91-80-51197777 ext 2018
email: shivg@xxxxxxxxxxx
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