Re: [PATCH v8 13/15] hw/pci: Use UINT32_MAX as a default value for rombar

[Markus Armbruster]

Akihiko Odaki <akihiko.odaki@daynix.com> writes:

> Currently there is no way to distinguish the case that rombar is
> explicitly specified as 1 and the case that rombar is not specified.
>
> Set rombar UINT32_MAX by default to distinguish these cases just as it
> is done for addr and romsize. It was confirmed that changing the default
> value to UINT32_MAX will not change the behavior by looking at
> occurences of rom_bar.
>
> $ git grep -w rom_bar
> hw/display/qxl.c:328:    QXLRom *rom = memory_region_get_ram_ptr(&d->rom_bar);
> hw/display/qxl.c:431:    qxl_set_dirty(&qxl->rom_bar, 0, qxl->rom_size);
> hw/display/qxl.c:1048:    QXLRom *rom = 
> memory_region_get_ram_ptr(&qxl->rom_bar);
> hw/display/qxl.c:2131:    memory_region_init_rom(&qxl->rom_bar, OBJECT(qxl), 
> "qxl.vrom",
> hw/display/qxl.c:2154: PCI_BASE_ADDRESS_SPACE_MEMORY, &qxl->rom_bar);
> hw/display/qxl.h:101:    MemoryRegion       rom_bar;
> hw/pci/pci.c:74:    DEFINE_PROP_UINT32("rombar",  PCIDevice, rom_bar, 1),
> hw/pci/pci.c:2329:    if (!pdev->rom_bar) {
> hw/vfio/pci.c:1019:    if (vdev->pdev.romfile || !vdev->pdev.rom_bar) {
> hw/xen/xen_pt_load_rom.c:29:    if (dev->romfile || !dev->rom_bar) {
> include/hw/pci/pci_device.h:150:    uint32_t rom_bar;
>
> rom_bar refers to a different variable in qxl. It is only tested if
> the value is 0 or not in the other places.
>
> If a user explicitly set UINT32_MAX, we still cannot distinguish that
> from the implicit default. However, it is unlikely to be a problem as
> nobody would type literal UINT32_MAX (0xffffffff or 4294967295) by
> chance.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>

Not exactly elegant, but I believe we have similar "default value means
not set by user (good enough because the default value is sufficiently
odd)" logic elsewhere.

Reviewed-by: Markus Armbruster <armbru@redhat.com>