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From: "Oliver O'Halloran" <oohall@gmail.com>
Date: Wed, 12 Jun 2019 16:16:12 +1000
Message-ID: <CAOSf1CEoEgWwD2qmBHiCG0B4JjmS0g=SUqm+OEYsbvv11QSARw@mail.gmail.com>
Subject: Re: [PATCH kernel v3 0/3] powerpc/ioda2: Yet another attempt to allow
 DMA masks between 32 and 59
To: Shawn Anastasio <shawn@anastas.io>
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Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
 Alistair Popple <alistair@popple.id.au>,
 David Gibson <david@gibson.dropbear.id.au>,
 linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
 Sam Bobroff <sbobroff@linux.ibm.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On Wed, Jun 12, 2019 at 3:06 PM Shawn Anastasio <shawn@anastas.io> wrote:
>
> On 6/5/19 11:11 PM, Shawn Anastasio wrote:
> > On 5/30/19 2:03 AM, Alexey Kardashevskiy wrote:
> >> This is an attempt to allow DMA masks between 32..59 which are not large
> >> enough to use either a PHB3 bypass mode or a sketchy bypass. Depending
> >> on the max order, up to 40 is usually available.
> >>
> >>
> >> This is based on v5.2-rc2.
> >>
> >> Please comment. Thanks.
> >
> > I have tested this patch set with an AMD GPU that's limited to <64bit
> > DMA (I believe it's 40 or 42 bit). It successfully allows the card to
> > operate without falling back to 32-bit DMA mode as it does without
> > the patches.
> >
> > Relevant kernel log message:
> > ```
> > [    0.311211] pci 0033:01     : [PE# 00] Enabling 64-bit DMA bypass
> > ```
> >
> > Tested-by: Shawn Anastasio <shawn@anastas.io>
>
> After a few days of further testing, I've started to run into stability
> issues with the patch applied and used with an AMD GPU. Specifically,
> the system sometimes spontaneously crashes. Not just EEH errors either,
> the whole system shuts down in what looks like a checkstop.

Any specific workload? Checkstops are harder to debug without a system
in the failed state so we'd need to replicate that locally to get a
decent idea what's up.

> Perhaps some subtle corruption is occurring?