Private bug reported:

With "Above 4G MMIO" enabled in BIOS, EFI FB driver cannot get 64-bit FB 
address on Raven1 platform.
Then fail to initialize EFI FB driver.

That results in black-screen for console mode or installing Ubuntu
system.

e.g. if the FB address is 0x7fc80000000, EFI FB could only get the low 32-bit 
FB address.
[    0.992990] efifb: probing for efifb
[    0.992995] efifb: cannot reserve video memory at 0x80000000
[    0.992999] ioremap on RAM at 0x0000000080000000 - 0x00000000808cffff


As my investigation, it looks Ubuntu efi boot stub cannot get 64-bit address by 
GOP.

1) create a EFI shell app to get the fb address, it’s 64-bit
2) Build bzImage.efi to load 4.13 custom kernel, efifb driver also could get 
64-bit address.

** Affects: amd
     Importance: High
         Status: New

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https://bugs.launchpad.net/bugs/1736862

Title:
  [Raven1] EFI FB driver cannot get 64-bit FB address with "Above 4G
  MMIO" enabled in Ubuntu16.04.3

Status in amd:
  New

Bug description:
  With "Above 4G MMIO" enabled in BIOS, EFI FB driver cannot get 64-bit FB 
address on Raven1 platform.
  Then fail to initialize EFI FB driver.

  That results in black-screen for console mode or installing Ubuntu
  system.

  e.g. if the FB address is 0x7fc80000000, EFI FB could only get the low 32-bit 
FB address.
  [    0.992990] efifb: probing for efifb
  [    0.992995] efifb: cannot reserve video memory at 0x80000000
  [    0.992999] ioremap on RAM at 0x0000000080000000 - 0x00000000808cffff

  
  As my investigation, it looks Ubuntu efi boot stub cannot get 64-bit address 
by GOP.

  1) create a EFI shell app to get the fb address, it’s 64-bit
  2) Build bzImage.efi to load 4.13 custom kernel, efifb driver also could get 
64-bit address.

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