On 20 February 2014 14:54, Srikanth Thokala <sthokal@xxxxxxxxxx> wrote: > On Wed, Feb 19, 2014 at 12:33 AM, Jassi Brar <jaswinder.singh@xxxxxxxxxx> wrote: >> On 18 February 2014 23:16, Srikanth Thokala <sthokal@xxxxxxxxxx> wrote: >>> On Tue, Feb 18, 2014 at 10:20 PM, Jassi Brar <jaswinder.singh@xxxxxxxxxx> wrote: >>>> On 18 February 2014 16:58, Srikanth Thokala <sthokal@xxxxxxxxxx> wrote: >>>>> On Mon, Feb 17, 2014 at 3:27 PM, Jassi Brar <jaswinder.singh@xxxxxxxxxx> wrote: >>>>>> On 15 February 2014 17:30, Srikanth Thokala <sthokal@xxxxxxxxxx> wrote: >>>>>>> The current implementation of interleaved DMA API support multiple >>>>>>> frames only when the memory is contiguous by incrementing src_start/ >>>>>>> dst_start members of interleaved template. >>>>>>> >>>>>>> But, when the memory is non-contiguous it will restrict slave device >>>>>>> to not submit multiple frames in a batch. This patch handles this >>>>>>> issue by allowing the slave device to send array of interleaved dma >>>>>>> templates each having a different memory location. >>>>>>> >>>>>> How fragmented could be memory in your case? Is it inefficient to >>>>>> submit separate transfers for each segment/frame? >>>>>> It will help if you could give a typical example (chunk size and gap >>>>>> in bytes) of what you worry about. >>>>> >>>>> With scatter-gather engine feature in the hardware, submitting separate >>>>> transfers for each frame look inefficient. As an example, our DMA engine >>>>> supports up to 16 video frames, with each frame (a typical video frame >>>>> size) being contiguous in memory but frames are scattered into different >>>>> locations. We could not definitely submit frame by frame as it would be >>>>> software overhead (HW interrupting for each frame) resulting in video lags. >>>>> >>>> IIUIC, it is 30fps and one dma interrupt per frame ... it doesn't seem >>>> inefficient at all. Even poor-latency audio would generate a higher >>>> interrupt-rate. So the "inefficiency concern" doesn't seem valid to >>>> me. >>>> >>>> Not to mean we shouldn't strive to reduce the interrupt-rate further. >>>> Another option is to emulate the ring-buffer scheme of ALSA.... which >>>> should be possible since for a session of video playback the frame >>>> buffers' locations wouldn't change. >>>> >>>> Yet another option is to use the full potential of the >>>> interleaved-xfer api as such. It seems you confuse a 'video frame' >>>> with the interleaved-xfer api's 'frame'. They are different. >>>> >>>> Assuming your one video frame is F bytes long and Gk is the gap in >>>> bytes between end of frame [k] and start of frame [k+1] and Gi != Gj >>>> for i!=j >>>> In the context of interleaved-xfer api, you have just 1 Frame of 16 >>>> chunks. Each chunk is Fbytes and the inter-chunk-gap(ICG) is Gk where >>>> 0<=k<15 >>>> So for your use-case ..... >>>> dma_interleaved_template.numf = 1 /* just 1 frame */ >>>> dma_interleaved_template.frame_size = 16 /* containing 16 chunks */ >>>> ...... //other parameters >>>> >>>> You have 3 options to choose from and all should work just as fine. >>>> Otherwise please state your problem in real numbers (video-frames' >>>> size, count & gap in bytes). >>> >>> Initially I interpreted interleaved template the same. But, Lars corrected me >>> in the subsequent discussion and let me put it here briefly, >>> >>> In the interleaved template, each frame represents a line of size denoted by >>> chunk.size and the stride by icg. 'numf' represent number of frames i.e. >>> number of lines. >>> >>> In video frame context, >>> chunk.size -> hsize >>> chunk.icg -> stride >>> numf -> vsize >>> and frame_size is always 1 as it will have only one chunk in a line. >>> >> But you said in your last post >> "with each frame (a typical video frame size) being contiguous in memory" >> ... which is not true from what you write above. Anyways, my first 2 >> suggestions still hold. > > Yes, each video frame is contiguous and they can be scattered. > I assume by contiguous frame you mean as in framebuffer? Which is an array of bytes. If yes, then you should do as I suggest first, frame_size=16 and numf=1. If no, then it seems you are already doing the right thing.... the ring-buffer scheme. Please share some stats how the current api is causing you overhead because that is a very common case (many controllers support LLI) and you have 467ms (@30fps with 16-frames ring-buffer) to queue in before you see any frame drop. Regards, Jassi -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
