[PATCH kernel v3 0/3] powerpc/ioda2: Yet another attempt to allow DMA masks between 32 and 59

[Shawn Anastasio]

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 at 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.

Perhaps some subtle corruption is occurring?