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[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

** Also affects: linux-raspi2 (Ubuntu Xenial)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1708417

Title:
  Board hangs with 'dtoverlay=vc4-kms-v3d' while writing to /dev/fb0

Status in linux-raspi2 package in Ubuntu:
  New
Status in linux-raspi2 source package in Xenial:
  New

Bug description:
  Impact:

  There is a kernel hang in 4.4.y if the vc4 driver is enabled, and
  another program opens /dev/fb0 to display an image.

  Fix:

  Apply the attached patch and recompile the kernel.

  How to test:

  Enable the gpu hardware acceleration by loading the vc4 overlay:

  config.txt:
  ...
  dtoverlay=vc4-kms-v3d
  ...

  reboot and check that vc4 was activated:

  $ dmesg | grep vc4

  ...
  [   15.274385] vc4-drm soc:gpu: bound 3f902000.hdmi (ops vc4_hdmi_ops [vc4])
  [   15.274660] vc4_dsi 3f700000.dsi: DSI not set up by firmware.
  [   15.274753] vc4-drm soc:gpu: bound 3f700000.dsi (ops vc4_dsi_ops [vc4])
  [   15.274873] vc4-drm soc:gpu: bound 3f400000.hvs (ops vc4_hvs_ops [vc4])
  [   15.275178] vc4-drm soc:gpu: bound 3f206000.pixelvalve (ops vc4_crtc_ops [vc4])
  [   15.275407] vc4-drm soc:gpu: bound 3f207000.pixelvalve (ops vc4_crtc_ops [vc4])
  [   15.275643] vc4-drm soc:gpu: bound 3f807000.pixelvalve (ops vc4_crtc_ops [vc4])
  [   15.275818] vc4-drm soc:gpu: bound 3fc00000.v3d (ops vc4_v3d_ops [vc4])
  [   15.403354] vc4-drm soc:gpu: fb0:  frame buffer device
  ...

  then download and compile psplash:

  $ git clone git://git.yoctoproject.org/psplash
  $ cd psplash
  $ autoreconf --install
  $ ./configure
  $ make
  $ sudo ./psplash

  here the board should hang, pull the plug to get it back.
  Now install the patched kernel, and execute psplash again - the board will be fine, and a bitmap will be displayed on hdmi, ctrl+c to exit psplash.

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