This far we have used the remap_pfn_range() function directly to map buffers to user space. Calling this function has worked as all memory allocations have been contiguous. However, the function must support also non-contiguous memory allocations as we later want to turn on IOMMU.
This patch modifies the code to use dma_mapping API for mapping buffers to user space.
Signed-off-by: Arto Merilainen amerilainen@nvidia.com ---
I tested this patch on cardhu using Hiroshi Doyu's series "Unified SMMU driver among Tegra SoCs" and using just pure Linux 3.12rc4. I have not tested this on T20 so I would appreaciate help in here (although I do not think this should affect the behavior on T20 at all).
I also would like to hear suggestions on better approaches for using dma_mmap_writecombine(). If IOMMU is not used, this function call ends up calling arm_iommu_mmap() which assumes that vm_pgoff value is valid. I see that other drm drivers simply implement fault callbacks and avoid this problem completely.
drivers/gpu/host1x/drm/gem.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/host1x/drm/gem.c b/drivers/gpu/host1x/drm/gem.c index 59623de..82ae3d5 100644 --- a/drivers/gpu/host1x/drm/gem.c +++ b/drivers/gpu/host1x/drm/gem.c @@ -240,6 +240,7 @@ int tegra_drm_mmap(struct file *file, struct vm_area_struct *vma) { struct drm_gem_object *gem; struct tegra_bo *bo; + unsigned long vm_pgoff; int ret;
ret = drm_gem_mmap(file, vma); @@ -249,8 +250,19 @@ int tegra_drm_mmap(struct file *file, struct vm_area_struct *vma) gem = vma->vm_private_data; bo = to_tegra_bo(gem);
- ret = remap_pfn_range(vma, vma->vm_start, bo->paddr >> PAGE_SHIFT, - vma->vm_end - vma->vm_start, vma->vm_page_prot); + /* the pages are real */ + vma->vm_flags &= ~VM_PFNMAP; + + /* drm holds a fake offset in vm_pgoff... dma_mapping assumes that + * vm_pgoff contains data related to the buffer => clear the cookie + * temporarily. */ + + vm_pgoff = vma->vm_pgoff; + vma->vm_pgoff = 0; + ret = dma_mmap_writecombine(bo->gem.dev->dev, vma, bo->vaddr, + bo->paddr, bo->gem.size); + vma->vm_pgoff = vm_pgoff; + if (ret) drm_gem_vm_close(vma);