> 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@xxxxxxxxxxxxx> 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! 😄
