Ok, I finally found the original patch from Vladimir. Comments below:
> +++ b/kernel/dma/direct.c
> @@ -456,14 +456,14 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
> #else /* CONFIG_MMU */
> bool dma_direct_can_mmap(struct device *dev)
> {
> - return false;
> + return true;
> }
>
> int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
> void *cpu_addr, dma_addr_t dma_addr, size_t size,
> unsigned long attrs)
> {
> - return -ENXIO;
> + return vm_iomap_memory(vma, vma->vm_start, (vma->vm_end - vma->vm_start));;
I think we should try to reuse the mmu dma_direct_mmap implementation,
which does about the same. This version has been compile tested on
arm-nommu only, let me know what you think: (btw, a nommu_defconfig of
some kind for arm would be nice..)
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index d006668c0027d2..e0dae570a51530 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -71,6 +71,7 @@ config SWIOTLB
# in the pagetables
#
config DMA_NONCOHERENT_MMAP
+ default y if !MMU
bool
config DMA_REMAP
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 0a4881e59aa7d6..9ec6a5c3fc578c 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -459,7 +459,6 @@ int dma_direct_get_sgtable(struct device *dev, struct sg_table *sgt,
return ret;
}
-#ifdef CONFIG_MMU
bool dma_direct_can_mmap(struct device *dev)
{
return dev_is_dma_coherent(dev) ||
@@ -485,19 +484,6 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
user_count << PAGE_SHIFT, vma->vm_page_prot);
}
-#else /* CONFIG_MMU */
-bool dma_direct_can_mmap(struct device *dev)
-{
- return false;
-}
-
-int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
- void *cpu_addr, dma_addr_t dma_addr, size_t size,
- unsigned long attrs)
-{
- return -ENXIO;
-}
-#endif /* CONFIG_MMU */
int dma_direct_supported(struct device *dev, u64 mask)
{
