On 11/03/2016 08:06 AM, Alexey Brodkin wrote: > We used to use generic implementation of dma_map_ops.mmap which is > dma_common_mmap() but that only worked for simpler cached mappings when > vaddr = paddr. > > If a driver requests uncached DMA buffer kernel maps it to virtual > address so that MMU gets involved and page uncached status takes into > account. In that case usage of dma_common_mmap() lead to mapping of > vaddr to vaddr for user-space which is obviously wrong. For more detals > please refer to verbose explanation here [1]. > > So here we implement our own version of mmap() which always deals > with dma_addr and maps underlying memory to user-space properly > (note that DMA buffer mapped to user-space is always uncached > because there's no way to properly manage cache from user-space). > > [1] https://lkml.org/lkml/2016/10/26/973 > > Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com> > Reviewed-by: Catalin Marinas <catalin.marinas at arm.com> > Cc: Marek Szyprowski <m.szyprowski at samsung.com> > Cc: Vineet Gupta <vgupta at synopsys.com> > Cc: <stable at vger.kernel.org> I've added a stable 4.5+, since ARC didn't use dma ops until 4.5-rc1. Pushed to for-curr ! Thx, -Vineet > --- > > Changes v1 -> v2: > * Added plat_dma_to_phys wrapper around dma_addr > > arch/arc/mm/dma.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/arch/arc/mm/dma.c b/arch/arc/mm/dma.c > index 20afc65e22dc..9288851d43a0 100644 > --- a/arch/arc/mm/dma.c > +++ b/arch/arc/mm/dma.c > @@ -105,6 +105,31 @@ static void arc_dma_free(struct device *dev, size_t size, void *vaddr, > __free_pages(page, get_order(size)); > } > > +static int arc_dma_mmap(struct device *dev, struct vm_area_struct *vma, > + void *cpu_addr, dma_addr_t dma_addr, size_t size, > + unsigned long attrs) > +{ > + unsigned long user_count = vma_pages(vma); > + unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT; > + unsigned long pfn = __phys_to_pfn(plat_dma_to_phys(dev, dma_addr)); > + unsigned long off = vma->vm_pgoff; > + int ret = -ENXIO; > + > + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > + > + if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret)) > + return ret; > + > + if (off < count && user_count <= (count - off)) { > + ret = remap_pfn_range(vma, vma->vm_start, > + pfn + off, > + user_count << PAGE_SHIFT, > + vma->vm_page_prot); > + } > + > + return ret; > +} > + > /* > * streaming DMA Mapping API... > * CPU accesses page via normal paddr, thus needs to explicitly made > @@ -193,6 +218,7 @@ static int arc_dma_supported(struct device *dev, u64 dma_mask) > struct dma_map_ops arc_dma_ops = { > .alloc = arc_dma_alloc, > .free = arc_dma_free, > + .mmap = arc_dma_mmap, > .map_page = arc_dma_map_page, > .map_sg = arc_dma_map_sg, > .sync_single_for_device = arc_dma_sync_single_for_device, >
