linux-kernel - Re: [PATCH 2/2] ARM: dts: imx7: add DMA properties for ECSPI

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Date:   Wed, 13 Feb 2019 00:07:17 +0000
From:   Trent Piepho <tpiepho@...inj.com>
To:     "festevam@...il.com" <festevam@...il.com>
CC:     "linux-imx@....com" <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "stefan@...er.ch" <stefan@...er.ch>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "fabio.estevam@....com" <fabio.estevam@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
Subject: Re: [PATCH 2/2] ARM: dts: imx7: add DMA properties for ECSPI

On Tue, 2019-02-12 at 17:37 -0200, Fabio Estevam wrote:
> On Mon, Feb 11, 2019 at 8:22 PM Trent Piepho <tpiepho@...inj.com>
> wrote:
> 
> > > Just trying to understand if the SDMA firmware plays a role on
> > > this
> > > behavior or not.
> > 
> > The ROM firmware only.
> 
> Does the problem also happen if the external SDMA firmware is used?
> Just trying to narrow it down.

Tried SDMA firmware 4.2.  Still broken.  No apparent change.

Get 4 cycle pause after each byte.

And crash while/after using DMA.  Clearly some sort of memory
corruption going on.  Fortunately, it's very reliable that using DMA
almost immediately causes a problem and this is easy to reproduce.  I
think that indicates it's either clobbers a lot of RAM, or consistently
manages to hit a very important location for kernel memory allocators.

I've got an idea of where that might be happening that I'm looking
into.

I think it's reasonable to add the dma attributes, but put a check in
the spi-imx driver to disable DMA on imx7d at least.