Dear all, I am reading LDD(V3) chapter 6 on the topic of wait_event(queue, condition) and wake_up(queue) functions. I am quite confused on the sayings. One is "Until condition evaluates to a true value, the process continues to sleep", which looks like that 'condition' is the one who wake up the process from its sleeping. However the other saying is "The basic function that wakes up sleeping processes is called wake_up, and wake_up wakes up all processes waiting on the given queue" So who is the exact one to wake the sleeping process up at all, condition or wake_up? From my understanding, if the condition becomes true, then the sleeping process will leave its sleeping status and wake up. Then what's the use of wake_up function?
My senario could be described as: in my char device driver, I use one ioctl command to initiate a DMA transfer. After all related registers are initiated, this process will be put to sleep for saving CPU cycles. In the interrupt handler which is for a DMA_done, I wake that process up and resume its following executing. With this method, in my application program if I release a DMA initiation command, it is a Blocking operation and it will wait until the DMA transfer is done. Perhaps my question is quite simple or basic. Thanks for any explanation and comment on this topic in my senario from you experts. Thanks a lot. Br Ming _________________________________________________________________ 与联机的朋友进行交流，请使用 MSN Messenger: http://messenger.msn.com/cn _______________________________________________ Linuxppc-embedded mailing list [email protected] https://ozlabs.org/mailman/listinfo/linuxppc-embedded
