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Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1

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On Thu, Sep 03, 2015 at 09:41:43PM +0800, Shawn Lin wrote:
> On 2015/9/3 20:54, Mark Brown wrote:

> >If this is a quirk of the DMA controller why is it being fixed with a
> >property specific to the SPI controller?  Can't the DMA controller just
> >override the burst size?

> Cool...that's a good question. Actually DMA controller can't do that since
> block peripheral controller(e.g sd/emmc, they always access data by
> block-512Bytes.) can't meet the case. So It's hard for dma controller know
> who is the caller, and what should be done.

You could take a guess based on request size, but that's going to be a
bit error prone I imagine.

> The only thing dma controller can do is avoid to execute DMAFLUSHP on its
> own. But how about peripheral controller trigger non-multiple access? So
> that's what I mentioned on covery letter that we should do "broken things"
> for both dma controller and some peripherals.

The other thing it could do is provide the information out via some
internal Linux API which the drivers could query instead of directly
having a DT property in each client driver.  That way at least the DT
only needs the quirk in one place even if the clients need to handle it
individually.

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Thread

[PATCH v3 0/9] Fix broken DMAFLUSHP on Rockchips platform Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:00 +0200
  [PATCH v3 6/9] ARM: dts: Add arm,pl330-broken-no-flushp quirk for rk3288 platform Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:00 +0200
  [PATCH v3 5/9] DMA: pl330: add quirk for broken no flushp Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:00 +0200
  [PATCH v3 1/9] DMA: pl330: support burst mode for dev-to-mem and mem-to-dev transmit Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:00 +0200
  [PATCH v3 2/9] Documentation: arm-pl330: add description of arm,pl330-broken-no-flushp Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:00 +0200
  [PATCH v3 3/9] Documentation: spi-rockchip: add description of rockchip,spi-broken-burst-len Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:00 +0200
  [PATCH v3 7/9] ARM: dts: Add arm,pl330-broken-no-flushp quirk for rk3xxx platform Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:00 +0200
  [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1 Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:10 +0200
    Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1 Mark Brown <broonie@kernel.org> - 2015-09-03 15:00 +0200
      Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1 Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-03 15:50 +0200
        Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1 Mark Brown <broonie@kernel.org> - 2015-09-03 20:50 +0200
          Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1 Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-04 02:10 +0200
  [PATCH v3 9/9] ASoC: rockchip_i2s: modify DMA max burst to 1 Shawn Lin <shawn.lin@rock-chips.com> - 2015-09-01 12:10 +0200

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