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Studying more of GRUB's video-drivers...
The EFI-GOP driver module-initializer checks if there's a suitable pseudofile with available video-modes before registering the driver. The module-finalizer might set the mode back before unregistering the driver.
The info&fini method reformats (via a helper) reformats EFI data into GRUB's generic format, if successful it defers to generic code & frees an additional framebuffer.
The render-target setter defers to generic code with a fallback value.
1/
Buffers are swapped via a `blt` firmware method, if the secondary framebuffer's available.
To get the EDID it opens a pseudofile with fallback to carefully retrieve its "agp-internal-edid" property. These pseudofiles & their properties are EFI-compliant firmware concepts.
The modes-iterator method wraps the `query_mode` firmware method in a for-loop, passing each reformatted (via a helper) entry to a given callback.
A further helper, used by the mode-info reformatter, handles bitmasks.
2/?
Whilst a shared helper calculates pixel bit-depth under different conditions.
The finalizer additionally considers calling the firmware-method to set the mode back & unconditionally frees the extra framebuffer. Whilst the initializer zeroes out the framebuffer.
The setup method gets fallback dimensions from the EDID, considers reformatting bitdepth from a value retrieved from the firmware, iterates over available video-modes choosing the best-fitting one, ...
3/?
... configures the firmware to use the found mode if any, reformats (via a shared helper) that mode, allocates the extra framebuffer, & carefully calls generic routines to initialize the main framebuffer.
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As for the SM712 video-driver...
Its info&fini method is the usual.
Buffer-swapping defers to generic code with additional cache-syncing.
There's numerous I/O helpers, whereas usually there's few if any. Ultimately it might compile down to printf()s for debugging/testing.
4/?
The finalizer might deregister the memory-mapped I/O before deferring to generic code. Whilst the initializer additionally zeroes out the framebuffer.
Then there's datastructures defining the language SM712 graphics cards speak.
The setup routine validates the given dimensions, locates the graphics card on the PCI bus & its framebuffer, fills in mode-info data for info&fini to return, possibly outputs some desired specs, registers memory-mapped I/O, sends an init output, ...
5/6!
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