On 04/25/2010 05:24 PM, Mauro Carvalho Chehab wrote:
Richard Röjfors wrote:
This patch adds the timberdale video-in driver.
The video IP of timberdale delivers the video data via DMA.
The driver uses the DMA api to handle DMA transfers, and make use
of the V4L2 videobuffers to handle buffers against user space.
Due to some timing constraint it makes sense to do DMA into an
intermediate buffer and then copy the data to vmalloc:ed buffers.
If available the driver uses an encoder to get/set the video standard
Signed-off-by: Richard Röjfors<richard.rojfors@xxxxxxxxxxxxxx>
+#define TIMBLOGIW_DMA_BUFFER_SIZE (TIMBLOGIW_BYTES_PER_LINE * 576)
...
+static int __timblogiw_alloc_dma(struct timblogiw_fh *fh, struct device *dev)
+{
+ dma_addr_t addr;
+ int err, i, pos;
+ int bytes_per_desc = TIMBLOGIW_LINES_PER_DESC *
+ timblogiw_bytes_per_line(fh->cur_norm);
+
+ fh->dma.cookie = -1;
+ fh->dma.dev = dev;
+
+ fh->dma.buf = kzalloc(TIMBLOGIW_DMA_BUFFER_SIZE, GFP_KERNEL);
+ if (!fh->dma.buf)
+ return -ENOMEM;
Why do you need a fixed DMA buffer size? Just allocate the buffer size dynamically at
buffer_prepare callback.
+ videobuf_queue_vmalloc_init(&fh->vb_vidq,&timblogiw_video_qops,
+ NULL,&fh->queue_lock, V4L2_BUF_TYPE_VIDEO_CAPTURE,
+ V4L2_FIELD_NONE, sizeof(struct videobuf_buffer), fh);
You should be using, instead, videobuf_dma_sg or videobuf_cont, instead of
using videobuf-vmalloc. This way, you'll avoid double buffering.
1. dma_sg can not be used, the DMA engine requires the memory blocks to be aligned on a factor of
bytes per line, so 4K pages wouldn't work.
2.
I tried using videobuf-dma-contig, but got poor performance. I can not really explain why, I though
it's due to the fact that the contiguous buffer is allocated coherent -> no caching.
I saw both gstreamer and mplayer perform very badly.
The frame grabber requires the DMA transfer for a frame beeing started while the frame is decoded.
When I tested using contigous buffers gstreamer sometimes was that slow that it sometimes missed to
have a frame queued when a transfer was finished, so I got frame drops. Any other ideas of the poor
performance? otherwise I would like to go for the double buffered solution.
Thanks
--Richard
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