On 03/26/2015 11:52 AM, Joerg Roedel wrote:
Hi Mark,
On Thu, Mar 26, 2015 at 10:58:15AM -0400, Mark Hounschell wrote:
Sorry but CMA was still badly broken. I have a patch below that works.
In which way is it broken? What happens when you try to allocate memory
with dma_alloc_coherent?
I got Oops on both the alloc and free and I had to hit the reset button.
I've tested it with small (no CMA) and large (with CMA) dma's using
dma_alloc_coherent. The patch below is just the "git diff" from your
cloned tree piped to a file then copied into this email. If you require
an official patch I can send one. Just let me know.
The main differences I can spot are that you change the order (first
CMA, then buddy) and you manually align the input size. I can see the
reason for the later, but why does CMA need to be tried first?
I believe that is how dma_alloc_coherent works. If CMA is present it
uses it. Even for small allocations. If not present then it does the
best it can. That patch was derived by looking at the Intel iommu driver
works properly. Maybe you should take a look at that.
Also, in my opinion, this CMA thing is clearly a BUG not a feature
request. The AMD iommu clearly breaks CMA. I feel what ever fix
you are happy with should be back ported to stable.
It is not a BUG, the interface definition for dma_alloc_coherent does
not specify that it can allocate infinite amounts of memory. So this
patch does not qualify for stable.
I don't care what the "the interface definition for dma_alloc_coherent"
says. If it does not describe it's use with CMA, it is outdated. Maybe
the "interface definition for dma_alloc_coherent" was done before CMA
was implemented.
Maybe you should be looking at CMA Documentation. Unfortunately there
does not yet seem to be any in the Documentation dir. Probably because
CMA is supposed to be transparent to the DMA API. You know, one should
not need to details about it, etc...
It is a BUG. To access CMA you use dma_alloc_coherent. You have
completely highjacked that function. You have broken CMA. PERIOD. That
is a BUG.
Regards
Mark
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