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Diffstat (limited to 'Documentation/gpu/todo.rst')
| -rw-r--r-- | Documentation/gpu/todo.rst | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst index 40ccac61137e..22ce801e3a8d 100644 --- a/Documentation/gpu/todo.rst +++ b/Documentation/gpu/todo.rst @@ -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 ============== |