On 11/29/2012 06:46 PM, Terje Bergström wrote:
On 29.11.2012 12:01, Mark Zhang wrote:
Just for curious, why "pb->mapped + 1K" is the end of a 4K pushbuffer?
pb->mapped is u32 *, so compiler will take care of multiplying by sizeof(u32).
Ah, yes. Sorry, I must be insane at that time. :)
+unsigned int nvhost_cdma_wait_locked(struct nvhost_cdma *cdma,
enum cdma_event event)+{
- for (;;) {
unsigned int space = cdma_status_locked(cdma, event);if (space)return space;/* If somebody has managed to already start waiting, yield */if (cdma->event != CDMA_EVENT_NONE) {mutex_unlock(&cdma->lock);schedule();mutex_lock(&cdma->lock);continue;}cdma->event = event;mutex_unlock(&cdma->lock);down(&cdma->sem);mutex_lock(&cdma->lock);I'm newbie of nvhost but I feel here is very tricky, about the lock and unlock of this mutex: cdma->lock. Does it require this mutex is locked before calling this function? And do we need to unlock it before the code: "return space;" above? IMHO, this is not a good design and can we find out a better solution?
Yeah, it's not perfect and good solutions are welcome. cdma_status_locked() must be called with a mutex. But, what we generally wait for is for space in push buffer. The cleanup code cannot run if we keep cdma->lock, so I release it.
The two ways to loop are because there was a race between two processes waiting for space. One of them set cdma->event to indicate what it's waiting for and can go to sleep, but the other has to keep spinning.
Alright. I just feel this mutex operations is complicated and error-prone, but I just get the big picture of nvhost and still don't know much about a lot of details. So I'll let you know if I find some better solutions.
Terje