The boot framebuffer is expected to be configured by the firmware, so it
uses fw_cfg as interface. Initialization goes as follows:
(1) Check whenever etc/ramfb is present.
(2) Allocate framebuffer from RAM.
(3) Fill struct RAMFBCfg, write it to etc/ramfb.
Done. You can write stuff to the framebuffer now, and it should appear
automagically on the screen.
Note that this isn't very efficient because it does a full display
update on each refresh. No dirty tracking. Dirty tracking would have
to be active for the whole ram slot, so that wouldn't be very efficient
either. For a boot display which is active for a short time only this
isn't a big deal. As permanent guest display something better should be
used (if possible).
This is the ramfb core code. Some windup is needed for display devices
which want have a ramfb boot display.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Message-id: 20180613122948.18149-2-kraxel@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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