[Qemu-devel] [Bug 1833101] Re: vexpress-a9 (but not -a15) creates two pl111 LCDs due to duplicate sysbus_create_simple("pl111", ...) calls

[Peter Maydell]

Our vexpress-a9 model instantiates two PL111s because the hardware has
two PL111s. One is on the daughterboard, at address 0x10020000, and the
other is on the motherboard, at address 0x40001F000.

The vexpress-a15 hardware has only one PL111, which is why you only see
one being created for that hardware. (Instead it has one PL111 and one
HDLCD controller, but QEMU has no model of the HDLCD controller at the
moment. We might add one one day.)

In an ideal world we would implement the video multiplexing that the
hardware does to allow the guest to select which of the two display
devices gets to send output (this is controlled by the SYS_CFG_MUXFPGA
system configuration register), at which point we'd be able to only show
a single screen window.

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https://bugs.launchpad.net/bugs/1833101

Title:
  vexpress-a9 (but not -a15) creates two pl111 LCDs due to duplicate
  sysbus_create_simple("pl111", ...) calls

Status in QEMU:
  New

Bug description:
  Hi,

  Just a small report that (12ec8bd is current master)

  https://github.com/qemu/qemu/blob/12ec8bd/hw/arm/vexpress.c#L652:

    ...
    vexpress_common_init() {
      ...
      sysbus_create_simple("pl111", map[VE_CLCD], pic[14]);
      ...
    ...

  and

  https://github.com/qemu/qemu/blob/12ec8bd/hw/arm/vexpress.c#L304:

    ...
    a9_daughterboard_init() {
      ...
      sysbus_create_simple("pl111", 0x10020000, pic[44]);
      ...
    ...

  result in two LCD panels when using vexpress-a9.

  vexpress-a15 does not appear to be affected (my -a9 kernel does not
  work with it, but I see only one pl111 created).

  Understandably (but still annoyingly), -nodefaults has no effect.

  This bug is most evident when using SDL (so I can use ",frame=off"),
  which dumps two top-level windows onto the screen. GTK hides this
  because, coincidentally, the pl111 that ends up being used is the one
  that is selected (possibly the one created last?), relegating this to
  an obscure glitch only noticeable if you scrutinize the menu.

  This is a bugreport as opposed to a pull request as I have no idea
  which call to remove - and complete ignorance of the potential
  housekeeping and consideration that may be warranted first.

  FWIW, a simple testcase can be made with the vmlinuz from
  https://people.debian.org/~aurel32/qemu/armhf/ and

  qemu-system-arm -M vexpress-a9 -kernel vmlinuz-3.2.0-4-vexpress
  -nodefaults -sdl

  Thanks!

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