Hi
This series tries to fix the mess with global system framebuffer access in device drivers. Currently, architecture initialization sets the "screen_info" object according to the system framebuffer that was detected during boot. The device driver that can map VMEM first gets access to it. There is no way to give a specific driver access to the device and no _proper_ way to revoke access again. In fact, some drivers don't even check whether they mapped the VMEM successfully, letting multiple drivers to access the system framebuffer at the same time.
This series introduces a new bus in patch #1. Global system framebuffers are added as devices to this bus and drivers can register as bus drivers. Via sysfs we can now bind/unbind the drivers. This guarantees that only one driver has access to a single system-framebuffer at a time. But we can also easily control which driver gets loaded (and extend this logic at a central place if we want).
If a real hardware drivers gets loaded via another bus that actually provides the system-framebuffer (like pci-bus), these drivers can use a special BUS function to claim the system framebuffer and unload all other drivers from this device. This can be used by _real_ DRM drivers that want to kill all other generic framebuffer drivers.
This series adds a SYSFB_VBE (VESA/VBE) framebuffer type as example, but the bus can be used with any other system-framebuffer type. Any other architecture can add their own type like SYSFB_VBE. Patch #3 is currently a HACK to provide the VBE framebuffer on all architectures. However, the platform-device for system-framebuffers should instead be provided by architecture code.
Why a new BUS type? We need a way to allow transition from a generic driver to a real hardware driver (like most DRM drivers or special fbdev drivers). We could implement this logic separately, but the BUS driver-core code is available, anyway. So lets use it and save a lot of .text space. Additionally, we get some extra features like driver binding/unbinding via sysfs for free (which is really handy for debugging). The new bus is actually implemented in <200 lines of code. I don't think we can get a smaller implementation when not using the bus-core code.
Patch #4 fixes vesafb.c to be hotplug-capable. It doesn't depend on this new bus so it would be nice if it could get applied right away. It allows vesafb to be compiled as a module.
Patch #5 makes vesafb.c register as new bus driver on the system-framebuffer bus.
Patch #6-#9 introduce DVBE. It's a DRM driver based on VBE/VESA. It also uses the new system-framebuffer bus and provides merely the same functionality as vesafb.c but with a sane user-space API and without any fbdev dependency.
What needs to be done? All drivers that use screen_info currently don't _have_ to be converted to the new bus as the request_memory() calls protect the drivers from interfering. So this new bus works even if no other driver gets converted. However, we really _should_ convert the drivers. I will do that if a maintainer agrees to take the bus code through their tree. But I hope to avoid converting all drivers if no maintainer thinks this bus is a good idea. The DVBE and vesafb drivers show how it is done.
I also like to see the system-framebuffer platform-devices being registered during architecture initialization. I haven't worked much there so any comments are welcome. Otherwise, I will keep the HACK to add the devices during sysfb module-init.
Regards David
David Herrmann (9): video: introduce system framebuffer bus video: sysfb: new vbefb device type video: sysfb: always provide vbefb device video: vesafb: allow building as module video: vesafb: use sysfb bus drm: new sysfb DRM bus module drm: new VESA BIOS Extension DRM driver stub drm: dvbe: implement VBE/VESA blitting backend drm: dvbe: add optional fbdev frontend
drivers/gpu/drm/Kconfig | 7 + drivers/gpu/drm/Makefile | 2 + drivers/gpu/drm/drm_sysfb.c | 145 +++++++++++++ drivers/gpu/drm/dvbe/Kconfig | 47 +++++ drivers/gpu/drm/dvbe/Makefile | 5 + drivers/gpu/drm/dvbe/dvbe.h | 121 +++++++++++ drivers/gpu/drm/dvbe/dvbe_drv.c | 104 +++++++++ drivers/gpu/drm/dvbe/dvbe_fbdev.c | 235 +++++++++++++++++++++ drivers/gpu/drm/dvbe/dvbe_main.c | 432 ++++++++++++++++++++++++++++++++++++++ drivers/gpu/drm/dvbe/dvbe_mem.c | 269 ++++++++++++++++++++++++ drivers/gpu/drm/dvbe/dvbe_vesa.c | 263 +++++++++++++++++++++++ drivers/video/Kconfig | 20 +- drivers/video/Makefile | 1 + drivers/video/sysfb.c | 315 +++++++++++++++++++++++++++ drivers/video/vesafb.c | 105 ++++----- include/drm/drmP.h | 4 + include/drm/drm_sysfb.h | 35 +++ include/linux/sysfb.h | 137 ++++++++++++ 18 files changed, 2197 insertions(+), 50 deletions(-) create mode 100644 drivers/gpu/drm/drm_sysfb.c create mode 100644 drivers/gpu/drm/dvbe/Kconfig create mode 100644 drivers/gpu/drm/dvbe/Makefile create mode 100644 drivers/gpu/drm/dvbe/dvbe.h create mode 100644 drivers/gpu/drm/dvbe/dvbe_drv.c create mode 100644 drivers/gpu/drm/dvbe/dvbe_fbdev.c create mode 100644 drivers/gpu/drm/dvbe/dvbe_main.c create mode 100644 drivers/gpu/drm/dvbe/dvbe_mem.c create mode 100644 drivers/gpu/drm/dvbe/dvbe_vesa.c create mode 100644 drivers/video/sysfb.c create mode 100644 include/drm/drm_sysfb.h create mode 100644 include/linux/sysfb.h