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Tuesday, 22 May 2012

PRIME dmabuf work picked up by ARM graphics open-source development

The Linux hybrid graphics community has grown massively in the last few years, and the large number of people with hybrid graphics laptops has spurred the development of tools to have these devices fully supported in Linux. Some of this great work, the PRIME dmabuf code developed by David Airlie, has now been applied to support ARM's next-generation GPU Mali chips. Tom Cooksey reports the developments below: 

For the last few months we (ARM MPD... "The Mali guys") have been working on
getting X.Org up and running with Mali T6xx (ARM's next-generation GPU IP).
The approach is very similar (well identical I think) to how things work on
OMAP: We use a DRM driver to manage the display controller via KMS. The KMS
driver also allocates both scan-out and pixmap/back buffers via the
DRM_IOCTL_MODE_CREATE_DUMB ioctl which is internally implemented with GEM.
When returning buffers to DRI clients, the x-server uses flink to get a
global handle to a buffer which it passes back to the DRI client (in our
case the Mali-T600 X11 EGL winsys). The client then uses the new PRIME
ioctls to export the GEM buffer it received from the x-server to a dma_buf
ioctls to export the GEM buffer it received from the x-server to a dma_buf
fd. This fd is then passed into the T6xx kernel driver via our own job
dispatch user/kernel API (we're not using DRM for driving the GPU, only the
display controller).