Merge tag 'drm-misc-next-2017-01-30' of git://anongit.freedesktop.org/git/drm-misc into drm-next

Another round of -misc stuff:
- Noralf debugfs cleanup cleanup (not yet everything, some more driver
  patches awaiting acks).
- More doc work.
- edid/infoframe fixes from Ville.
- misc 1-patch fixes all over, as usual

Noralf needs this for his tinydrm pull request.

* tag 'drm-misc-next-2017-01-30' of git://anongit.freedesktop.org/git/drm-misc: (48 commits)
  drm/vc4: Remove vc4_debugfs_cleanup()
  dma/fence: Export enable-signaling tracepoint for emission by drivers
  drm/tilcdc: Remove tilcdc_debugfs_cleanup()
  drm/tegra: Remove tegra_debugfs_cleanup()
  drm/sti: Remove drm_debugfs_remove_files() calls
  drm/radeon: Remove drm_debugfs_remove_files() call
  drm/omap: Remove omap_debugfs_cleanup()
  drm/hdlcd: Remove hdlcd_debugfs_cleanup()
  drm/etnaviv: Remove etnaviv_debugfs_cleanup()
  drm/etnaviv: allow build with COMPILE_TEST
  drm/amd/amdgpu: Remove drm_debugfs_remove_files() call
  drm/prime: Clarify DMA-BUF/GEM Object lifetime
  drm/ttm: Make sure BOs being swapped out are cacheable
  drm/atomic: Remove drm_atomic_debugfs_cleanup()
  drm: drm_minor_register(): Clean up debugfs on failure
  drm: debugfs: Remove all files automatically on cleanup
  drm/fourcc: add vivante tiled layout format modifiers
  drm/edid: Set YQ bits in the AVI infoframe according to CEA-861-F
  drm/edid: Set AVI infoframe Q even when QS=0
  drm/edid: Introduce drm_hdmi_avi_infoframe_quant_range()
  ...

1 files changed, 16 insertions, 3 deletions

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 8d77b2462594..25aa4558f1b5 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -40,8 +40,11 @@
  * On the export the dma_buf holds a reference to the exporting GEM
  * object. It takes this reference in handle_to_fd_ioctl, when it
  * first calls .prime_export and stores the exporting GEM object in
- * the dma_buf priv. This reference is released when the dma_buf
- * object goes away in the driver .release function.
+ * the dma_buf priv. This reference needs to be released when the
+ * final reference to the &dma_buf itself is dropped and its
+ * &dma_buf_ops.release function is called. For GEM-based drivers,
+ * the dma_buf should be exported using drm_gem_dmabuf_export() and
+ * then released by drm_gem_dmabuf_release().
  *
  * On the import the importing GEM object holds a reference to the
  * dma_buf (which in turn holds a ref to the exporting GEM object).
@@ -51,6 +54,16 @@
  * when the imported object is destroyed, we remove the attachment
  * and drop the reference to the dma_buf.
  *
+ * When all the references to the &dma_buf are dropped, i.e. when
+ * userspace has closed both handles to the imported GEM object (through the
+ * FD_TO_HANDLE IOCTL) and closed the file descriptor of the exported
+ * (through the HANDLE_TO_FD IOCTL) dma_buf, and all kernel-internal references
+ * are also gone, then the dma_buf gets destroyed.  This can also happen as a
+ * part of the clean up procedure in the drm_release() function if userspace
+ * fails to properly clean up.  Note that both the kernel and userspace (by
+ * keeeping the PRIME file descriptors open) can hold references onto a
+ * &dma_buf.
+ *
  * Thus the chain of references always flows in one direction
  * (avoiding loops): importing_gem -> dmabuf -> exporting_gem
  *
@@ -291,7 +304,7 @@ static void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
  * This wraps dma_buf_export() for use by generic GEM drivers that are using
  * drm_gem_dmabuf_release(). In addition to calling dma_buf_export(), we take
  * a reference to the &drm_device and the exported &drm_gem_object (stored in
- * exp_info->priv) which is released by drm_gem_dmabuf_release().
+ * &dma_buf_export_info.priv) which is released by drm_gem_dmabuf_release().
  *
  * Returns the new dmabuf.
  */