[Qemu-devel] [Bug 1752646] [NEW] Freezing VNC screen on some the UEFI framebuffer applications

[Leonid Myravjev]

Public bug reported:

Hi folks!

I use TianCore (UEFI) formware on the qemu (master version last commit a6e0344).
When kernel/linux is start, it using UEFI Framebuffer. Then I run UEFI 
application (which writes directly to the framebuffer) my VNS screen is 
freezing. Then I restart vnclient I see only one frame.

When I run application, I getting in the file hw/display/vga.c on
function 'vga_ioport_write' some commands, it change "s->ar_index" from
0x20 -> 0x10

In the function vga_update_display:
1751         if (!(s->ar_index & 0x20)) {
1752             graphic_mode = GMODE_BLANK;
1753         } else {

And I got GMODE_BLANK mode. If I patch it:
1751         if (0) {

my VNC not freezing.

>From "Hardware Level VGA and SVGA Video Programming Information Page" I
saw, what ar_index is 0x3C0 (Attribute Controller Data Write Register),
0x20(5-bit) is PAS -- Palette Address Source

If there is a output via the UEFI framebuffer, does the difference have
a PAS or not? Why do we need to pause the output if the PAS is exposed?
Especially when the application outputs via framebuffer.

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: framebuffer uefi vga

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https://bugs.launchpad.net/bugs/1752646

Title:
  Freezing VNC screen on some the UEFI framebuffer applications

Status in QEMU:
  New

Bug description:
  Hi folks!

  I use TianCore (UEFI) formware on the qemu (master version last commit 
a6e0344).
  When kernel/linux is start, it using UEFI Framebuffer. Then I run UEFI 
application (which writes directly to the framebuffer) my VNS screen is 
freezing. Then I restart vnclient I see only one frame.

  When I run application, I getting in the file hw/display/vga.c on
  function 'vga_ioport_write' some commands, it change "s->ar_index"
  from 0x20 -> 0x10

  In the function vga_update_display:
  1751         if (!(s->ar_index & 0x20)) {
  1752             graphic_mode = GMODE_BLANK;
  1753         } else {

  And I got GMODE_BLANK mode. If I patch it:
  1751         if (0) {

  my VNC not freezing.

  From "Hardware Level VGA and SVGA Video Programming Information Page"
  I saw, what ar_index is 0x3C0 (Attribute Controller Data Write
  Register), 0x20(5-bit) is PAS -- Palette Address Source

  If there is a output via the UEFI framebuffer, does the difference
  have a PAS or not? Why do we need to pause the output if the PAS is
  exposed? Especially when the application outputs via framebuffer.

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