On Thu, 23 Sep 2010, Janusz Krzysztofik wrote:
Thursday 23 September 2010 15:33:54 Guennadi Liakhovetski napisał(a):
On Wed, 22 Sep 2010, Janusz Krzysztofik wrote:
Wednesday 22 September 2010 01:23:22 Guennadi Liakhovetski napisał(a):
On Sat, 11 Sep 2010, Janusz Krzysztofik wrote:
- vb = &buf->vb;
- if (waitqueue_active(&vb->done)) {
if (!pcdev->ready && result != VIDEOBUF_ERROR)/** No next buffer has been entered into the DMA* programming register set on time, so best we can do* is stopping the capture before last DMA block,* whether our CONTIG mode whole buffer or its last* sgbuf in SG mode, gets overwritten by next frame.*/Hm, why do you think it's a good idea? This specific buffer completed successfully, but you want to fail it just because the next buffer is missing? Any specific reason for this?
Maybe my comment is not clear enough, but the below suspend_capture() doesn't indicate any failure on a frame just captured. It only prevents the frame from being overwritten by the already autoreinitialized DMA engine, pointing back to the same buffer once again.
Besides, you seem to also be considering the possibility of your ->ready == NULL, but the queue non-empty, in which case you just take the next buffer from the queue and continue with it. Why error out in this case?
pcdev->ready == NULL means no buffer was available when it was time to put it into the DMA programming register set.
But how? Buffers are added onto the list in omap1_videobuf_queue() under spin_lock_irqsave(); and there you also check ->ready and fill it in.
Guennadi, Yes, but only if pcdev->active is NULL, ie. both DMA and FIFO are idle, never if active:
- list_add_tail(&vb->queue, &pcdev->capture);
- vb->state = VIDEOBUF_QUEUED;
- if (pcdev->active)
return;Since the transfer of the DMA programming register set content to the DMA working register set is done automatically by the DMA hardware, this can pretty well happen while I keep the lock here, so I can't be sure if it's not too late for entering new data into the programming register set. Then, I decided that this operation should be done only just after the DMA interrupt occured, ie. the current DMA programming register set content has just been used and can be overwriten.
I'll emphasize the above return; with a comment.
Ok
In your completion you set ->ready = NULL, but then also call prepare_next_vb() to get the next buffer from the list - if there are any, so, how can it be NULL with a non-empty list?
It happens after the above mentioned prepare_next_vb() gets nothing from an empty queue, so nothing is entered into the DMA programming register set, only the last, just activated, buffer is processed, then omap1_videobuf_queue() puts a new buffer into the queue while the active buffer is still filled in, and finally the DMA ISR is called on this last active buffer completion.
I hope this helps.
Let's assume it does:) You seem to really understand how this is working and even be willing to document the driver, thus making it possibly the best documented soc-camera related piece of software;)
Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/