[PATCH 0/2] drm: add SimpleDRM driver

Noralf Trønnes
2016-08-04T14:10:56Z

This patchset adds the simpledrm driver by David Herrmann based on a
patchset[1] from 2014. That patchset also included patches for kicking
out simpledrm by real drivers. I have stayed away from that since it
involves another subsystem and I would probably be unable to answer any
questions about the implementation.

I have done my best to bring simpledrm up to speed. However I was unable to
loose drm_legacy_mmap() in sdrm_drm_mmap() since I don't understand much of
the gem code.

I was left with some questions after doing this:

- Is there any reason why simpledrm can't use drm_gem_cma_helper?
One obvious difference is that of contiguous memory allocation:

sdrm_gem_get_pages():
obj->pages = drm_malloc_ab(num, sizeof(*obj->pages));
for (i = 0; i < num; ++i) {
obj->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
obj->vmapping = vmap(obj->pages, num, 0, PAGE_KERNEL);

drm_gem_cma_create():
cma_obj->vaddr = dma_alloc_wc(drm->dev, size, &cma_obj->paddr,
GFP_KERNEL | __GFP_NOWARN);

- Could we set this range to the actual width/height of the native framebuffer?

sdrm_drm_modeset_init():
ddev->mode_config.min_width = 1;
ddev->mode_config.min_height = 1;
ddev->mode_config.max_width = 8192;
ddev->mode_config.max_height = 8192;

- Is there a usecase for offsetting the dumb buffer when blitted onto the
native buffer?

sdrm_blit():
/* get scanout offsets */
xoff = 0;
yoff = 0;
if (sdrm->pipe.plane.fb == fb) {
xoff = sdrm->pipe.crtc.x;
yoff = sdrm->pipe.crtc.y;
}

I have tested simpledrm on a Raspberry Pi B+ with U-boot setting up the
framebuffer and producing this node:

framebuffer@1e887000 {
compatible = "simple-framebuffer";
reg = <0x1e887000 0x36c600>;
format = "r5g6b5";
width = <1824>;
height = <984>;
stride = <3648>;
status = "okay";
};

I have only tested with fbcon and modetest (XR24,RG16).

Noralf.

Changes from previous version[2]:
- Remove FB_SIMPLE=n dependency to avoid kconfig recursive error
- Changed module name to match kconfig help text: sdrm -> simpledrm
- Use drm_simple_display_pipe
- Replace deprecated drm_platform_init()
- sdrm_dumb_create(): drm_gem_object_unreference() -> *_unlocked()
- sdrm_dumb_map_offset(): drm_gem_object_lookup() remove drm_device parameter
- sdrm_drm_mmap() changes:
Remove struct_mutex locking
Add drm_vma_offset_{lock,unlock}_lookup()
drm_mmap() -> drm_legacy_mmap()
- dma_buf_begin_cpu_access() doesn't require start and length anymore
- Use drm_cvt_mode() instead of open coding a mode
- Fix format conversion. In the intermediate step, store the 8/6/5 bit color
value in the upper part of the 16-bit color variable, not the lower.
- Support clips == NULL in sdrm_dirty()
- Set mode_config.preferred_depth
- Attach mode_config.dirty_info_property to connector
fbdev:
- Remove the DRM_SIMPLEDRM_FBDEV kconfig option and use DRM_FBDEV_EMULATION
- Suspend fbcon/fbdev when the pipeline is enabled, resume in lastclose
- Add FBINFO_CAN_FORCE_OUTPUT flag so we get oops'es on the console

[1] https://lists.freedesktop.org/archives/dri-devel/2014-January/052584.html
[2] https://lists.freedesktop.org/archives/dri-devel/2014-January/052594.html

Further history:

[PATCH v4 0/6] SimpleDRM Driver
https://lists.freedesktop.org/archives/dri-devel/2013-September/044638.html

[PATCH v2 00/14] Platform Framebuffers and SimpleDRM
https://lists.freedesktop.org/archives/dri-devel/2013-July/041090.html

[RFC 0/6] SimpleDRM Driver (was: dvbe driver)
https://lists.freedesktop.org/archives/dri-devel/2013-June/040386.html

[PATCH 0/9] System Framebuffer Bus (sysfb)
https://lists.freedesktop.org/archives/dri-devel/2013-February/035013.html

Noralf Trønnes (2):
drm: add SimpleDRM driver
drm: simpledrm: add fbdev fallback support

drivers/gpu/drm/Kconfig | 2 +
drivers/gpu/drm/Makefile | 1 +
drivers/gpu/drm/simpledrm/Kconfig | 22 ++
drivers/gpu/drm/simpledrm/Makefile | 5 +
drivers/gpu/drm/simpledrm/simpledrm.h | 111 ++++++++++
drivers/gpu/drm/simpledrm/simpledrm_damage.c | 314 +++++++++++++++++++++++++++
drivers/gpu/drm/simpledrm/simpledrm_drv.c | 298 +++++++++++++++++++++++++
drivers/gpu/drm/simpledrm/simpledrm_fbdev.c | 160 ++++++++++++++
drivers/gpu/drm/simpledrm/simpledrm_gem.c | 276 +++++++++++++++++++++++
drivers/gpu/drm/simpledrm/simpledrm_kms.c | 288 ++++++++++++++++++++++++
10 files changed, 1477 insertions(+)
create mode 100644 drivers/gpu/drm/simpledrm/Kconfig
create mode 100644 drivers/gpu/drm/simpledrm/Makefile
create mode 100644 drivers/gpu/drm/simpledrm/simpledrm.h
create mode 100644 drivers/gpu/drm/simpledrm/simpledrm_damage.c
create mode 100644 drivers/gpu/drm/simpledrm/simpledrm_drv.c
create mode 100644 drivers/gpu/drm/simpledrm/simpledrm_fbdev.c
create mode 100644 drivers/gpu/drm/simpledrm/simpledrm_gem.c
create mode 100644 drivers/gpu/drm/simpledrm/simpledrm_kms.c

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2.8.2