I promised to study GRUB's IEEE1275 driver today, but after looking at my notes I believe I've already done so. As such I'll move onto some of the video-drivers GRUB has organized into submodules!
The CoreBoot framebuffer is handled specially by that port's initializer, with locating it within CoreBoot's lookuptable happening early.
The info&fini method is the usual. And the initializer additional (as usual) zeroes out the framebuffer.
1/4?
The setup method validates the state & requested dimensions, reencodes (via a helper) various format properties, extracts the actual framebuffer, & calls generic routines to initialize it.
GRUB includes video driver to LibSDL, which almost certainly serves to make it easier to debug their code. Since that's the sort of thing I've seen them do!
The render-target defers to a generic routine with a fallback value. Depending on the version of LibSDL it might swap buffers using SDL_Flip().
2/4?
But for LibSDL2 GRUB combines SDL_UpdateTexture(), SDL_RenderClear(), SDL_RenderCopy(), & SDL_Present() with error handling.
The palette setter reformats its args to hand off to the corresponding LibSDL API, or defers to a generic routine depending on the framebuffer's format.
The initializer & finalizer additionally calls SDL_Init() or SDL_Quit() & zeroes out the framebuffer.
The setup method fills in fallback dimensions, ...
3/4?
... carefully inits the LibSDL render target (on SDL2 this is a window, renderer, texture, & in-turn RGB-surface; otherwise just a window), zeroes out the framebuffer, gathers actual specs, & calls generic routines + the palette setter to init the framebuffer. A helper reformats bitmasks.
For i386 PCs there's VGA & VBE video-drivers...
It swaps buffers by ensuring (aided by a helper) its in a clean state & there's space, swaps properties, spinlocks on the hardware, & outputs new pointer.
4/6?
GRUB's VGA driver's palette-setter throws an error.
The setup&fini method outputs a mask of 15, copies a property over to the caller filling in various constants, offsets a framebuffer pointer, calls a generic routine, & frees a temporary buffer.
Its render-target getter falls back to the generic routine filling in a fallback value. The setter does the same, whilst tracking a flag.
The blit routines additionally uses that shared helper to ensure every "plane" is in a consistent state.
5/6?
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