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Re: [PATCH-for-6.2 0/2] hw/display: Do not allow multiple (identical) VG

From: Mark Cave-Ayland
Subject: Re: [PATCH-for-6.2 0/2] hw/display: Do not allow multiple (identical) VGA devices
Date: Fri, 19 Nov 2021 08:21:43 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0

On 18/11/2021 19:20, Philippe Mathieu-Daudé wrote:

Commit 7852a77f598 fixed creating multiple TYPE_ISA_VGA devices,
generalize the fix to all VGA devices.

See https://gitlab.com/qemu-project/qemu/-/issues/44

Philippe Mathieu-Daudé (2):
   hw/display: Add Error* handle to vga_common_init()
   hw/display: Do not allow multiple identical VGA devices

  hw/display/vga_int.h        |  2 +-
  hw/display/ati.c            |  4 +++-
  hw/display/cirrus_vga.c     |  4 +++-
  hw/display/cirrus_vga_isa.c |  4 +++-
  hw/display/qxl.c            |  4 +++-
  hw/display/vga-isa-mm.c     |  3 ++-
  hw/display/vga-isa.c        | 11 ++---------
  hw/display/vga-pci.c        |  8 ++++++--
  hw/display/vga.c            | 17 ++++++++++++++++-
  hw/display/virtio-vga.c     |  4 +++-
  hw/display/vmware_vga.c     |  2 +-
  11 files changed, 43 insertions(+), 20 deletions(-)

Hi Phil,

I don't think this is correct for non-ISA devices: for example years ago I had a PC running Windows 98SE with 2 identical PCI graphics cards configured in dual-head mode.

IIRC the BIOS would bring up the first graphics card and configure it to use the legacy ISA VGA ioports for compatibility, and then once the main OS drivers loaded both cards were switched to PCI mode and configured using the BARs as normal.



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