drm/fbdev: Add fbdev-shmem

Add an fbdev emulation for SHMEM-based memory managers. The code is
similar to fbdev-generic, but does not require an additional shadow
buffer for mmap(). Fbdev-shmem operates directly on the buffer object's
SHMEM pages. Fbdev's deferred-I/O mechanism updates the hardware state
on write operations.

The memory pages of GEM SHMEM cannot be detected by fbdefio. Therefore
fbdev-shmem implements the .get_page() hook in struct fb_deferred_io.
The fbdefio helpers call this hook to retrieve the page directly from
fbdev-shmem instead of trying to detect it internally.

v3:
- clarify on get_page mechanism in commit description (Javier)
v2:
- use drm_driver_legacy_fb_format() (Geert)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240419083331.7761-9-tzimmermann@suse.de

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index f9ca4f8fa6c5..fc793c6dd299 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -108,6 +108,7 @@ drm_dma_helper-$(CONFIG_DRM_KMS_HELPER) += drm_fb_dma_helper.o
 obj-$(CONFIG_DRM_GEM_DMA_HELPER) += drm_dma_helper.o
 
 drm_shmem_helper-y := drm_gem_shmem_helper.o
+drm_shmem_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fbdev_shmem.o
 obj-$(CONFIG_DRM_GEM_SHMEM_HELPER) += drm_shmem_helper.o
 
 drm_suballoc_helper-y := drm_suballoc.o