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(+)
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.
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! 😄
dri-devel@lists.freedesktop.org
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Alyssa Rosenzweig -
Robin Murphy