Open Firmware provides basic display output via the 'display' node.
DT platform code already provides a device that represents the node's
framebuffer. Add a DRM driver for the device. The display mode and
color format is pre-initialized by the system's firmware. Runtime
modesetting via DRM is not possible. The display is useful during
early boot stages or as error fallback.

Similar functionality is already provided by fbdev's offb driver,
which is insufficient for modern userspace. The old driver includes
support for BootX device tree, which can be found on old 32-bit
PowerPC Macintosh systems. If these are still in use, the
functionality can be added to ofdrm or implemented in a new
driver. As with simepldrm, the fbdev driver cannot be selected is
ofdrm is already enabled.

Two noteable points about the driver:

 * Reading the framebuffer aperture from the device tree is not
reliable on all systems. Ofdrm takes the heuristics and a comment
from offb to pick the correct range.

 * No resource management may be tied to the underlying PCI device.
Otherwise the handover to the native driver will fail with a resource
conflict. PCI management is therefore done as part of the platform
device's cleanup.

The driver has been tested on qemu's ppc64le emulation. The device
hand-over has been tested with bochs.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 MAINTAINERS                   |   1 +
 drivers/gpu/drm/tiny/Kconfig  |  12 +
 drivers/gpu/drm/tiny/Makefile |   1 +
 drivers/gpu/drm/tiny/ofdrm.c  | 748 ++++++++++++++++++++++++++++++++++
 drivers/video/fbdev/Kconfig   |   1 +
 5 files changed, 763 insertions(+)
 create mode 100644 drivers/gpu/drm/tiny/ofdrm.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 43d833273ae9..090cbe1aa5e3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -6395,6 +6395,7 @@ L:	dri-devel@lists.freedesktop.org
 S:	Maintained
 T:	git git://anongit.freedesktop.org/drm/drm-misc
 F:	drivers/gpu/drm/drm_aperture.c
+F:	drivers/gpu/drm/tiny/ofdrm.c
 F:	drivers/gpu/drm/tiny/simpledrm.c
 F:	include/drm/drm_aperture.h
 

diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
index 627d637a1e7e..0bc54af42e7f 100644
--- a/drivers/gpu/drm/tiny/Kconfig
+++ b/drivers/gpu/drm/tiny/Kconfig

@@ -51,6 +51,18 @@ config DRM_GM12U320
 	 This is a KMS driver for projectors which use the GM12U320 chipset
 	 for video transfer over USB2/3, such as the Acer C120 mini projector.
 
+config DRM_OFDRM
+	tristate "Open Firmware display driver"
+	depends on DRM && MMU && PPC