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Re: [PATCH v6 10/10] ASoC: rockchip_i2s: modify DMA max burst to 1

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On 10/15/2015 03:36 AM, Shawn Lin wrote:
[...]
> +
> +	if (snd_dmaengine_pcm_get_caps(&pdev->dev, &dma_caps) == 0) {
> +		if (dma_caps.max_burst > 4) {
> +			i2s->playback_dma_data.maxburst = 4;
> +			i2s->capture_dma_data.maxburst = 4;
> +		} else {
> +			i2s->playback_dma_data.maxburst = 1;
> +			i2s->capture_dma_data.maxburst = 1;

So this is what this is all about? I though you might have to program some
FIFO threshold registers in the peripheral itself.

But it seems all this does is to read the maximum burst length from the DMA
controller only to tell the DMA controller that this is the maximum burst
length it should use. That seems rather unnecessary.

The maxburst field of the dma_data indicates the maximum burst length that
the audio peripheral can handle. Typically this is the number of samples the
audio FIFO can receive without overflowing after sending the DMA request
signal. Since as the name suggests this is the maximum burst size the DMA
controller is free to choose a burst size smaller than this when writing
data to the peripheral.

So in your case instead of introducing all these facilities to query the
maximum burst size it should be OK to simply reduce the burst size in the
DMA controller itself when it gets a request with a burst size larger than
it can handle, or is there a reason why this is not possible?

- Lars
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Thread

[PATCH v6 0/10] Fix broken DMAFLUSHP on Rockchips platform Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
  [PATCH v6 04/10] ARM: dts: Add arm,pl330-broken-no-flushp quirk for rk3288 platform Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
  [PATCH v6 01/10] DMA: pl330: support burst mode for dev-to-mem and mem-to-dev transmit Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
    Re: [PATCH v6 01/10] DMA: pl330: support burst mode for dev-to-mem  and mem-to-dev transmit Vinod Koul <vinod.koul@intel.com> - 2015-10-15 06:10 +0200
      Re: [PATCH v6 01/10] DMA: pl330: support burst mode for dev-to-mem  and mem-to-dev transmit Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 09:00 +0200
  [PATCH v6 02/10] Documentation: arm-pl330: add description of arm,pl330-broken-no-flushp Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
  [PATCH v6 05/10] ARM: dts: Add arm,pl330-broken-no-flushp quirk for rk3xxx platform Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
  [PATCH v6 10/10] ASoC: rockchip_i2s: modify DMA max burst to 1 Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
    Re: [PATCH v6 10/10] ASoC: rockchip_i2s: modify DMA max burst to  1 Lars-Peter Clausen <lars@metafoo.de> - 2015-10-15 11:00 +0200
      Re: [PATCH v6 10/10] ASoC: rockchip_i2s: modify DMA max burst to 1 Jianqun Xu <jay.xu@rock-chips.com> - 2015-10-15 12:50 +0200
  [PATCH v6 07/10] DMA: pl330: add max burst for dmaengine Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
  [PATCH v6 03/10] DMA: pl330: add quirk for broken no flushp Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
  [PATCH v6 06/10] DMA: dmaengine: expose max burst capability to clients Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 03:40 +0200
  [PATCH v6 08/10] spi: rockchip: modify DMA max burst to 1 Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 04:00 +0200
  [PATCH v6 09/10] snd: dmaengine-pcm: add snd_dmaengine_pcm_get_caps interface Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 04:00 +0200
    Re: [alsa-devel] [PATCH v6 09/10] snd: dmaengine-pcm: add  snd_dmaengine_pcm_get_caps interface kbuild test robot <lkp@intel.com> - 2015-10-15 05:10 +0200
    Re: [PATCH v6 09/10] snd: dmaengine-pcm: add  snd_dmaengine_pcm_get_caps interface Vinod Koul <vinod.koul@intel.com> - 2015-10-15 06:10 +0200
      Re: [PATCH v6 09/10] snd: dmaengine-pcm: add  snd_dmaengine_pcm_get_caps interface Shawn Lin <shawn.lin@rock-chips.com> - 2015-10-15 09:00 +0200

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