This patchset adds support for simple-framebuffer platform devices and a handover mechanism for native drivers to take-over control of the hardware.
The new driver, called simpledrm, binds to a simple-framebuffer platform device. The kernel's boot code creates such devices for firmware-provided framebuffers, such as EFI-GOP or VESA. Typically the BIOS, UEFI or boot loader sets up the framebuffers. Description via device tree is also an option.
Simpledrm is small enough to be linked into the kernel. The driver's main purpose is to provide graphical output during the early phases of the boot process, before the native DRM drivers are available. Native drivers are typically loaded from an initrd ram disk. Occationally simpledrm can also serve as interim solution on graphics hardware without native DRM driver.
So far distributions rely on fbdev drivers, such as efifb, vesafb or simplefb, for early-boot graphical output. However fbdev is deprecated and the drivers do not provide DRM interfaces for modern userspace.
Patches 1 and 2 prepare the DRM format helpers for simpledrm.
Patches 4 to 8 add the simpledrm driver. It's build on simple DRM helpers and SHMEM. It supports 16-bit, 24-bit and 32-bit RGB framebuffers. During pageflips, SHMEM buffers are copied into the framebuffer memory, similar to cirrus or mgag200. The code in patches 7 and 8 handles clocks and regulators. It's based on the simplefb drivers, but has been modified for DRM. These patches will be squashed into one for the merger, so that the result is bisectable.
Patches 3 and 9 add a hand-over mechanism. Simpledrm acquires it's framebuffer's I/O-memory range and can be hot-unplugged by a native driver. The native driver will remove simpledrm before taking over the hardware. The removal is integrated into existing helpers, so existing drivers use it automatically.
I've also been working on fastboot support (i.e., flicker-free booting). This requires state-readout from simpledrm via generic interfaces, as outlined in [1]. I do have some prototype code, but it will take a while to get this ready. Simpledrm will then support it.
I've tested simpledrm with x86 EFI and VESA framebuffers, which both work reliably. The fbdev console and Weston work automatically. Xorg requires manual configuration of the device. Xorgs current modesetting driver does not work with both, platform and PCI device, for the same physical hardware. Once configured, X11 works. I looked into X11, but couldn't see an easy way of fixing the problem. With the push towards Wayland+Xwayland I expect the problem to become a non-issue soon. Additional testing has been reported at [2].
One cosmetical issue is that simpledrm's device file is card0 and the native driver's device file is card1. After simpledrm has been kicked out, only card1 is left. This does not seem to be a practical problem however.
TODO/IDEAS: * provide deferred takeover * provide bootsplash DRM client * make simplekms usable with ARM-EFI fbs
v5: * fix build error introduced by rebasing v4 * fix typo in documenation v4: * provide interface for acquiring firmware framebuffers (Daniel) * make simpledrm and simplefb mutually exclusive (Maxime) * documentation fixes v3: * clear screen to black when disabled (Daniel) * rebase onto existing aperture helpers * detach via hot-unplug via platform_device_unregister() v2: * rename to simpledrm, aperture helpers * reorganized patches * use hotplug helpers for removal (Daniel) * added DT match tables (Rob) * use shadow-plane helpers * lots of minor cleanups
[1] https://lore.kernel.org/dri-devel/CAKMK7uHtqHy_oz4W7F+hmp9iqp7W5Ra8CxPvJ=9Bw... [2] https://lore.kernel.org/dri-devel/1761762.3HQLrFs1K7@nerdopolis/
Thomas Zimmermann (9): drm/format-helper: Pass destination pitch to drm_fb_memcpy_dstclip() drm/format-helper: Add blitter functions drm/aperture: Add infrastructure for aperture ownership drm: Add simpledrm driver drm/simpledrm: Add fbdev emulation drm/simpledrm: Initialize framebuffer data from device-tree node drm/simpledrm: Acquire clocks from DT device node drm/simpledrm: Acquire regulators from DT device node drm/simpledrm: Acquire memory aperture for framebuffer
MAINTAINERS | 7 + drivers/gpu/drm/drm_aperture.c | 221 +++++- drivers/gpu/drm/drm_format_helper.c | 96 ++- drivers/gpu/drm/mgag200/mgag200_mode.c | 2 +- drivers/gpu/drm/tiny/Kconfig | 16 + drivers/gpu/drm/tiny/Makefile | 1 + drivers/gpu/drm/tiny/cirrus.c | 2 +- drivers/gpu/drm/tiny/simpledrm.c | 896 +++++++++++++++++++++++++ drivers/video/fbdev/Kconfig | 2 +- include/drm/drm_aperture.h | 4 + include/drm/drm_format_helper.h | 10 +- 11 files changed, 1245 insertions(+), 12 deletions(-) create mode 100644 drivers/gpu/drm/tiny/simpledrm.c
base-commit: bf25e1addaf44137e20ce95de72ff118b37d808c prerequisite-patch-id: c2b2f08f0eccc9f5df0c0da49fa1d36267deb11d prerequisite-patch-id: c67e5d886a47b7d0266d81100837557fda34cb24 prerequisite-patch-id: c59ca2ddb182af06006fa360ad3e90fe16b93d3a prerequisite-patch-id: dd15fb5fe2130e0dbf2fb7df6cae76d808ef6816 prerequisite-patch-id: 90618028e0df10398d6a0e4ae261e1e855905d38 prerequisite-patch-id: 3ee4d936e76da021ac3ea2dea586582813263876 prerequisite-patch-id: 8f302cdd86509f93ae2f573718264a7fb332c098 prerequisite-patch-id: b4b1d4a05a1db29696b3aea8572ff982677ec4b5 prerequisite-patch-id: 2a9db4556e8ecf0f2f2caa23ee288579d00ae002 -- 2.31.1