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authorGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-03-15 08:36:41 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2021-03-15 08:36:41 +0100
commit83be46e944f630fde26ce03cb93f61a3066448e3 (patch)
treed94a48051f9311d99b615fa06adda2511f9cff2d /Documentation/gpu/todo.rst
parentf8096ff38d5f62d8a2c473e1bec0163a1b2b86d8 (diff)
parent1e28eed17697bcf343c6743f0028cc3b5dd88bf0 (diff)
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Merge v5.12-rc3 into char-misc-next
We need the char/misc fixes in here as well. Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@@ -613,6 +613,27 @@ Some of these date from the very introduction of KMS in 2008 ...
Level: Intermediate
+Remove automatic page mapping from dma-buf importing
+----------------------------------------------------
+
+When importing dma-bufs, the dma-buf and PRIME frameworks automatically map
+imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and
+drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach()
+even if they never do actual device DMA, but only CPU access through
+dma_buf_vmap(). This is a problem for USB devices, which do not support DMA
+operations.
+
+To fix the issue, automatic page mappings should be removed from the
+buffer-sharing code. Fixing this is a bit more involved, since the import/export
+cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over
+this problem for USB devices by fishing out the USB host controller device, as
+long as that supports DMA. Otherwise importing can still needlessly fail.
+
+Contact: Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter
+
+Level: Advanced
+
+
Better Testing
==============