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

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On 2015/9/4 1:45, Mark Brown wrote:
> 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.
>

yes, not always cover all cases.

>> 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.

Good idea. Thanks, Mark.

>


-- 
Best Regards
Shawn Lin

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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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