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. -- Tixy > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > index 51d5352e6ad5..558434c69612 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -162,7 +162,7 @@ void __init arm64_memblock_init(void) > } > > early_init_fdt_scan_reserved_mem(); > - dma_contiguous_reserve(0); > + dma_contiguous_reserve(dma_to_phys(NULL, DMA_BIT_MASK(32)) + 1); > > memblock_allow_resize(); > memblock_dump_all(); > > probably with a check for IS_ENABLED(CONFIG_ZONE_DMA) (we do this for > swiotlb initialisation). > > At some point, if we have some system topology description we could > decide whether we need to limit the above based on the dma coherent > masks. > -- 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
