[PATCH] ath10k: fix system hang at qca99x0 probe on x86 platform

[Manoharan, Rajkumar]

On June 30, 2016 12:39 PM, Michal Kazior <michal.kazior at tieto.com> wrote:
> On 29 June 2016 at 18:35, Manoharan, Rajkumar <rmanohar at qti.qualcomm.com> wrote:
>>>> Am 29.06.2016 um 16:04 schrieb Sebastian Gottschall:
>>>> this fix will crash QCA9980 on QCA IPQ8064 cpu based systems.
>>>> so please rework it, or leave it out.
>>>> note:
>>>> maybe the limit of 256kb is too low for that card
>>>>
>>> by the way. 512 works
>
> I think this suggests the problem isn't about memory chunk size limit
> per se but some kind of bug in address/offset logic in fw or hw.
> 
> DMA coherent and single-map addresses use completely different ranges
> in many cases. Perhaps some MSBs are not properly handled in fw or hw.
> I recall there is a magic macro through which target device accesses
> host memory so maybe that's a good place to look to better understand
> the problem?
> 
Michał,

Could you please shed some light on this issue? It seems this issue is popping up
more frequently and there are multiple threads for this issue.

"Anyone brought up 9984 NIC on x86-64?"
"AR9882 IOMMU faults"

> I recall Ben mentioned he worked around the problem by enabling
> IOMMU/VT-d on his system. This could either prevent the device from
> doing bad things or maybe changed DMA address ranges that are handed
> out to the driver effectively or changed PCI controller behavior in
> some way.
>
>> Thanks a lot Sebastian. Let me confirm the same on x86 and will update the change.
> 
> Just changing the memory chunk size limit blindly is bad and
> Sebastian's crash has proven it. 512 may seem to work now but it may
> fail with a other 10.4 firmware revisions or make x86 hang in other
> cases.
> 
Even with current logic, If the memory chunk allocation fails for bigger size, then it tries
to allocate smaller chunks. So If smaller chunks causes unexpected behaviour, it is even
applicable to existing logic. no?

-Rajkumar