This code was added in b65e64f7ccd4 ("drm/cma: Use
dma_mmap_writecombine() to mmap buffer"), but does not explain why
it's needed.It should be entirely unnecessary, because remap_pfn_range(), which is what the various dma_mmap functiosn are built on top of, does already unconditionally adjust the vma flags: https://elixir.bootlin.com/linux/v6.1-rc6/source/mm/memory.c#L2518 More importantly, it does uncondtionally set VM_PFNMAP, so clearing that does not make much sense. Patch motived by discussions around enforcing VM_PFNMAP semantics for all dma-buf users, where Thomas asked why dma helpers will work with that dma_buf_mmap() contract. References: https://lore.kernel.org/dri-devel/[email protected]/ Cc: Laurent Pinchart <[email protected]> Cc: Dave Airlie <[email protected]> Cc: Maarten Lankhorst <[email protected]> Cc: Maxime Ripard <[email protected]> Cc: Thomas Zimmermann <[email protected]> Cc: Sumit Semwal <[email protected]> Cc: "Christian König" <[email protected]> Signed-off-by: Daniel Vetter <[email protected]> --- drivers/gpu/drm/drm_gem_dma_helper.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/drm_gem_dma_helper.c b/drivers/gpu/drm/drm_gem_dma_helper.c index 1e658c448366..637a5cc62457 100644 --- a/drivers/gpu/drm/drm_gem_dma_helper.c +++ b/drivers/gpu/drm/drm_gem_dma_helper.c @@ -525,13 +525,10 @@ int drm_gem_dma_mmap(struct drm_gem_dma_object *dma_obj, struct vm_area_struct * int ret; /* - * Clear the VM_PFNMAP flag that was set by drm_gem_mmap(), and set the - * vm_pgoff (used as a fake buffer offset by DRM) to 0 as we want to map - * the whole buffer. + * Set the vm_pgoff (used as a fake buffer offset by DRM) to 0 as we + * want to map the whole buffer. */ vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node); - vma->vm_flags &= ~VM_PFNMAP; - vma->vm_flags |= VM_DONTEXPAND; if (dma_obj->map_noncoherent) { vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); -- 2.37.2
