drm: Begin an API for in-kernel clients

This the beginning of an API for in-kernel clients.
First out is a way to get a framebuffer backed by a dumb buffer.

Only GEM drivers are supported.
The original idea of using an exported dma-buf was dropped because it
also creates an anonomous file descriptor which doesn't work when the
buffer is created from a kernel thread. The easy way out is to use
drm_driver.gem_prime_vmap to get the virtual address, which requires a
GEM object. This excludes the vmwgfx driver which is the only non-GEM
driver apart from the legacy ones. A solution for vmwgfx will have to be
worked out later if it wants to support the client API which it probably
will when we have a bootsplash client.

Suggested-by: Daniel Vetter <[email protected]>
Signed-off-by: Noralf Trønnes <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: notro

Documentation/gpu/drm-client.rst

@@ -0,0 +1,12 @@
+=================
+Kernel clients
+=================
+
+.. kernel-doc:: drivers/gpu/drm/drm_client.c
+   :doc: overview
+
+.. kernel-doc:: include/drm/drm_client.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_client.c
+   :export:

Documentation/gpu/index.rst

@@ -10,6 +10,7 @@ Linux GPU Driver Developer's Guide
    drm-kms
    drm-kms-helpers
    drm-uapi
+   drm-client
    drivers
    vga-switcheroo
    vgaarbiter

drivers/gpu/drm/Makefile

@@ -18,7 +18,7 @@ drm-y       :=	drm_auth.o drm_bufs.o drm_cache.o \
 		drm_encoder.o drm_mode_object.o drm_property.o \
 		drm_plane.o drm_color_mgmt.o drm_print.o \
 		drm_dumb_buffers.o drm_mode_config.o drm_vblank.o \
-		drm_syncobj.o drm_lease.o drm_writeback.o
+		drm_syncobj.o drm_lease.o drm_writeback.o drm_client.o
 
 drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_DRM_VM) += drm_vm.o