DMA issues on PowerPC64

[Jared Bents]

Hi all,

Some background information first.  I transitioned a build from 32 bit
to 64 bit and discovered my wifi modules no longer work.  I am using
fsl-v2.0-1703 on a qoriq t1042.  I sourced the problem to DMA mapping
errors and found that it was trying to map addresses in regions not
allowed by the kernel.

ath10k_pci 0001:01:00.0: unable to get target info from device
ath10k_pci 0001:01:00.0: could not get target info (5)
ath10k_pci 0001:01:00.0: could not probe fw (5)


I discovered that if I limited my memory from the actual 8GB present
down to just 2GB with the bootarg mem=2048M, the ath10k modules
worked.

So I started poking around in ath10k/pci.c and noticed that if I ORed
the regions specified in the memory allocations with GFP_DMA, I could
get rid of the initial dma mapping errors.  A couple of examples are
below.

skb = __dev_alloc_skb(pipe->buf_sz, GFP_DMA | GFP_ATOMIC);
treq = kmemdup(req, req_len, GFP_DMA | GFP_KERNEL);


But then came across these failures which I have yet to sort out.

ath10k_pci 0001:01:00.0: failed to connect htt (-5)
ath10k_pci 0001:01:00.0: could not init core (-5)
ath10k_pci 0001:01:00.0: could not probe fw (-5)


I am wondering if anyone else has come across this issue and solved it
or if somehow this is just an issue on ppc64 and I am somehow the only
one in that use case.  Unfortunately because of the qoriq t1042, I am
on the latest kernel I can use via the latest available sdk for my
processor which is linux kernel version 4.1.35-rt41

Thank you,
Jared