On Mon, May 19, 2014 at 09:21:17AM +0100, Jon Medhurst (Tixy) wrote: > On Fri, 2014-05-16 at 18:40 +0100, Catalin Marinas wrote: > > On Fri, May 16, 2014 at 06:08:45PM +0100, Jon Medhurst (Tixy) wrote: > > > On Fri, 2014-05-16 at 13:55 +0100, Catalin Marinas wrote: > > > [...] > > > > > It could if arm64 would restrict the DMA addresses to 32-bit, but it doesn't > > > > > and I end up on my platform with USB DMA buffers allocated >4GB address. > > > > > > > > dma_alloc_coherent() on arm64 should return 32-bit addresses if the > > > > coherent_dma_mask is set to 32-bit. > > > > > > Not if you have CONFIG_DMA_CMA. Unless I have misread the code, enabling > > > CMA means memory comes from a common pool carved out at boot with no way > > > for drivers to specify it's restrictions [1]. It's what I've spent most > > > of the week trying to work around in a clean way, and have finally given > > > up. > > > > The easiest "hack" would be to pass a limit dma_contiguous_reserve() > > in arm64_memblock_init(), something like this: > > That is by far the easiest but I dismissed it because it affects all > platforms built from that source tree; and if the hack were extended to > include a kernel config option, that still may not work on a single > kernel binary expected to work on multiple platforms. Basically, I've > tried various was to do it 'properly' and after failing am resorting to > truly hideous hacks to the (out-of-tree driver) code - so at least other > platforms won't be impacted. Can you set a specific reserved memory region in the DT to be used by CMA (via linux,cma-default), or it's just for the default size? On arm64 we enabled CONFIG_DMA_CMA by default but compared to swiotlb it doesn't honour GFP_DMA. The arm32 port sets the CMA limit to arm_dma_limit which is 32-bit or a SoC-define one. So I'm tempted to default to 32-bit as well if it can be overridden via DT. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
