linux-kernel - Re: [PATCH v2] ARM: dts: imx6dl: disable dma support for spi on i.mx6dl

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Date:	Tue, 16 Sep 2014 11:41:55 +0200
From:	Alexander Holler <holler@...oftware.de>
To:	Robin Gong <b38343@...escale.com>
CC:	shawn.guo@...escale.com, kernel@...gutronix.de, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	fugang.duan@...escale.com
Subject: Re: [PATCH v2] ARM: dts: imx6dl: disable dma support for spi on i.mx6dl

Am 16.09.2014 05:52, schrieb Robin Gong:
> On Mon, Sep 15, 2014 at 01:50:02PM +0200, Alexander Holler wrote:
>> Am 10.09.2014 07:30, schrieb Robin Gong:
>>> There is one weird data in rxfifo after one full rx/tx transfer
>>> done sometimes. It looks a design issue and hard to workaround
>>> totally, so disable dma functhion here. And will re-enable it
>>> once the root cause found.
>>
>> Hmm, I experience problems with DMA too but on uart3. I'm using the same
>> workaround for the uart (I've just commented out the dma entries in the DT).
>> The problem manifests itself here such, that brcm_patchram_plus
>> hangs while uploading the firmware to a BCM4330 connected at uart3
>> (reproducible).
>>
>> So maybe there is a bug in the DMA-engine which not only effects
>> SPI. Or both drivers contain the same error in handling DMA (maybe
>> through c&p).
>> But that's just specualtion from me, I haven't looked further into
>> that problem.
>>
>> Regards,
>>
>> Alexander Holler
> Thanks for your information share. But my issue should be caused by hardware,
> since everything is ok if it runs on other i.mx6 chip. Is your board also based
> on i.mx6 chip? If yes, hope you can raise your issue in freescale community or
> contact with Andy whose mail address added in CC list fugang.duan@...escale.cm.
> We have fix some bugs in UART DMA case.

It's an i.mx6q (Wandboard quad c1) where I have this problem with 
mainline and much older (but heavily patched freescale 3.10.x based) 
kernels. A quick web-search suggests that this problem exists since a 
long time (noticed mainly by people which try to use BT as this seems to 
be the major use case for high speed serial communication).

Regards,

Alexander Holler
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