| Message ID | 1c68be0449aa3217e2bbc898dd8c7426748fc6b8.1629902585.git.robin.murphy@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/cma-helper: Set VM_DONTEXPAND for mmap | expand |
> drm_gem_cma_mmap() cannot assume every implementation of dma_mmap_wc() > will end up calling remap_pfn_range() (which happens to set the relevant > vma flag, among others), so in order to make sure expectations around > VM_DONTEXPAND are met, let it explicitly set the flag like most other > GEM mmap implementations do. > > This avoids repeated warnings on a small minority of systems where the > display is behind an IOMMU, and has a simple driver which does not > override drm_gem_cma_default_funcs. Apple system-on-chips have their display behind an IOMMU. Actually, a separate IOMMU for each display, and a separate IOMMU for each display controller -- so there are 4 IOMMUs total for display on the M1. I've tested this patch against my work-in-progress display driver for the M1. It indeed fixes the annoying warnings every frame (wayland) and on mode setting (x11). So this is Tested-by: Alyssa Rosenzweig <alyssa@rosenzweig.io> I've cherry-picked the patch into my M1 staging/downstream tree, so I guess that's an Acked-by. I don't know anything about the vm_* stuff in the kernel yet, though, since can't give a reviewed-by. Will leave that one to the pro's. I know you were trying to fix an HDLCD issue, but I needed this patch too, so thank you!
diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c index d53388199f34..63e48d98263d 100644 --- a/drivers/gpu/drm/drm_gem_cma_helper.c +++ b/drivers/gpu/drm/drm_gem_cma_helper.c @@ -510,6 +510,7 @@ int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) */ vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node); vma->vm_flags &= ~VM_PFNMAP; + vma->vm_flags |= VM_DONTEXPAND; cma_obj = to_drm_gem_cma_obj(obj);
drm_gem_cma_mmap() cannot assume every implementation of dma_mmap_wc() will end up calling remap_pfn_range() (which happens to set the relevant vma flag, among others), so in order to make sure expectations around VM_DONTEXPAND are met, let it explicitly set the flag like most other GEM mmap implementations do. This avoids repeated warnings on a small minority of systems where the display is behind an IOMMU, and has a simple driver which does not override drm_gem_cma_default_funcs. Signed-off-by: Robin Murphy <robin.murphy@arm.com> --- drivers/gpu/drm/drm_gem_cma_helper.c | 1 + 1 file changed, 1 insertion(+)