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@xxxxxxxxxx>
---
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);
--
1.8.1.5
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