Messages in this thread | | | Date | Sun, 25 Apr 2010 18:01:23 +0200 | From | Richard Röjfors <> | Subject | Re: [PATCH 1/2] media: Add timberdale video-in driver |
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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@pelagicore.com> >> +#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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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