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

[Michal Kazior]

On 20 July 2016 at 07:44, Adrian Chadd <adrian at freebsd.org> wrote:
> Hi,
>
> dma coherent doesn't /have/ to mean "low 32 bits". It's just supposed
> to mean "try really hard to use uncached memory on platforms that
> support it."

Good point. Maybe it does on x86, or at least some machines.

@Ben: Can you verify if that's the case for you? Can you see what
address ranges hostmem chunks get with and without the GFP_DMA32 (and
maybe compare it against a revert to compare to dma-coherent as well)?


> The ath10k hardware (at least what I've played with thus far) is all
> 32 bit DMA hardware, not 64 bit, so it can't be handed 64 bit memory -
> contiguous or otherwise.
>
> So, if dma coherent on linux means 32 bit only physmem, great.
>
> Now, it also turns out that various platforms that say they do
> coherent memory these days do "mostly coherent", and you still need
> some flush/sync ops..

Yeah, but since the device has it's own CPU and RAM it has to have a
way to distinguish local and host memory in some way using these 32
bits, no? (think about firmware generating local 802.11 frames vs
pushing frames coming from host driver)


Michał