Re: [edk2-discuss] Load Option passing. Either bugs or my confusion.

[Laszlo Ersek]

On 04/20/20 16:13, Gerd Hoffmann wrote:
>   Hi,
>
>> So I would say that the symptom you see is a QEMU v4.1.0 regression.
>> The QemuRamfbGraphicsOutputSetMode() function in the OVMF ramfb
>> driver certainly needs the QemuFwCfgWriteBytes() call to work, for
>> changing the resolution.
>
> Oh?  QemuRamfbGraphicsOutputSetMode() can be called multiple times?
> How does that happen?

QemuRamfbGraphicsOutputSetMode() is the "SetMode" member function of the
EFI_GRAPHICS_OUTPUT_PROTOCOL instance that QemuRamfbDxe produces.

This is a standard protocol; UEFI drivers and applications are free to
locate it and to use it.

(1) When you launch OVMF, you get the splash screen in a particular
resolution. This resolution:
- is configured by OvmfPkg/PlatformDxe,
- is inherited by an OS boot loader,
- is reconfigurable with OvmfPkg/PlatformDxe, for the next boot, via the
  Setup TUI,
- defaults to 800x600 (taking effect when no particular choice is
  configured).

(2) UiApp -- the Setup TUI itself -- uses its own resolution. Under
OVMF, this resolution is fixed 640x480. When UiApp is entered,
ultimately a call is made to QemuRamfbGraphicsOutputSetMode() -- i.e., a
GOP.SetMode() member function -- for setting this 640x480 resolution.

Using the following command:

  qemu-system-x86_64 \
    -nodefaults \
    -boot menu=on,splash-time=5000 \
    -enable-kvm \
    -device ramfb \
    -drive 
if=pflash,readonly,format=raw,file=$PREFIX/share/qemu/edk2-x86_64-code.fd \
    -drive 
if=pflash,snapshot,format=raw,file=$PREFIX/share/qemu/edk2-i386-vars.fd \
    -debugcon file:ovmf.log \
    -global isa-debugcon.iobase=0x402

when you first see the progress bar, the graphical resolution (1) is
800x600. Accordingly, QEMU prints to stderr:

> ramfb_fw_cfg_write: 800x600 @ 0x6702000

Once you hit ESC to interrupt the progress bar and to enter the Setup
TUI, UiApp switches to resolution (2), 640x480. QEMU prints:

> ramfb_fw_cfg_write: 640x480 @ 0x6702000
> ramfb_fw_cfg_write: resolution locked, change rejected

And you get garbage in the Setup window.

Thanks,
Laszlo