Showing the residual in petitboot menu when connecting the VGA device

[chcyjoy]

We found VGA or OpenBMC Web KVM will show the residual in petitboot menu when connecting the VGA device. There's no problem in serial console or BMC port 2200.

• Platform:
  Mihawk

• FW version:
  Opbuild: v2.3-rc2-409-g6ad3be1
  Buildroot: 2019.05.2-11-g8e3337d
  Skiboot: v6.5.1
  Hostboot: a8024a3
  Occ: 3472e6c
  Linux: 5.3.7-openpower1-p1406925
  Petitboot: v1.10.4
  Machinexml: f6ec5aa
  Hostbootbinaries: hw080119a.940
  Cappucode: p9-dd2-v4
  Sbe: 53c1726
  Hcode: hw102619a.op940

• Reproduce steps:

1. Connect a local VGA device to Mihawk machine
2. Host power on
3. Boot into Petitboot
4. Enter system information, system configuration or system status log
5. Go back to petitboot menu. The residual shows in VGA device or Web KVM
   
   Here's the video.
   residual_in_petiboot.zip

• Current Petitboot patch we used for this issue:
  https://github.com/alvintpwang/petitboot/commit/cba327862bacf0f133438b3cc7e39d78c8d762b7.patch

[chcyjoy]

@jk-ozlabs Could you please help us check this issue?