[PATCH] drm: Fix for GEM buffers with write-combine memory

[Paul Cercueil]

The previous commit wrongly assumed that dma_mmap_wc() could be replaced
by pgprot_writecombine() + dma_mmap_pages(). It did work on my setup,
but did not work everywhere.

Use dma_mmap_wc() when the buffer has the write-combine cache attribute,
and dma_mmap_pages() when it has the non-coherent cache attribute.

Signed-off-by: Paul Cercueil <p...@crapouillou.net>
Reported-by: Tomi Valkeinen <tomi.valkei...@ideasonboard.com>
Fixes: cf8ccbc72d61 ("drm: Add support for GEM buffers backed by non-coherent 
memory")
---
 drivers/gpu/drm/drm_gem_cma_helper.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c 
b/drivers/gpu/drm/drm_gem_cma_helper.c
index 235c7a63da2b..4c3772651954 100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -514,13 +514,17 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj, struct 
vm_area_struct *vma)
 
        cma_obj = to_drm_gem_cma_obj(obj);
 
-       vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
-       if (!cma_obj->map_noncoherent)
-               vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+       if (cma_obj->map_noncoherent) {
+               vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
+
+               ret = dma_mmap_pages(cma_obj->base.dev->dev,
+                                    vma, vma->vm_end - vma->vm_start,
+                                    virt_to_page(cma_obj->vaddr));
+       } else {
+               ret = dma_mmap_wc(cma_obj->base.dev->dev, vma, cma_obj->vaddr,
+                                 cma_obj->paddr, vma->vm_end - vma->vm_start);
 
-       ret = dma_mmap_pages(cma_obj->base.dev->dev,
-                            vma, vma->vm_end - vma->vm_start,
-                            virt_to_page(cma_obj->vaddr));
+       }
        if (ret)
                drm_gem_vm_close(vma);
 
-- 
2.30.2