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

[Michal Kazior]

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?

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.


Michał