On Thu, Jan 10, 2019 at 03:15:35PM -0800, Tyrel Datwyler wrote: > On a secondary note I was unaware of the GFP_ATOMIC limitations. Should this be > added to the documentation somewhere? I don't see any mention here form > DMA-API-HOWTO.txt. The DMA documentation unfortauntely doesn't seem very good. It's been on my todo list to eventually update it, but I'm still discoverying various warts. GFP_ATOMIC allocations generally work fine on DMA coherent architectures, but tend to cause problems on a lot of non-coherent ones with the notable exceptions of arm and arm64 that go to great length to introduce special pools for them. But that code is rarely exercised, so I found various bugs e.g. in the arm64 iommu code for this case. But more importantly there really should be no need for the coherent allocation from irq context - we only need coherent for descriptors that don't have clear ownership, and aything allocated in the I/O path generally has that.
