Re: [PATCH 3/3] sam460ex: Use type cast macro instead of simple cast

[Greg Kurz <groug@kaod.org>]

On Wed, 6 Jan 2021 16:24:01 +0100
BALATON Zoltan via <qemu-ppc@nongnu.org> wrote:

> Use the PCI_BUS type cast macro to convert result of
> qdev_get_child_bus(). Also remove the check for NULL afterwards which
> should not be needed because sysbus_create_simple() uses error_abort

It seems to me that sysbus_create_simple() doesn't return NULL because
it ends up calling object_new_with_type(). This allocates the object
with either g_malloc() or qemu_memalign(), both of which abort on
failure.

> and PCI_BUS macro also checks its argument by default so this

AFAICT, PCI_BUS() and all other instance type checking macros are
happy with a NULL argument. They simply return NULL in this case.

> shouldn't fail here.
> 
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> ---
>  hw/ppc/sam460ex.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/ppc/sam460ex.c b/hw/ppc/sam460ex.c
> index 14e6583eb0..cc67e9c39b 100644
> --- a/hw/ppc/sam460ex.c
> +++ b/hw/ppc/sam460ex.c
> @@ -384,11 +384,8 @@ static void sam460ex_init(MachineState *machine)
>      ppc460ex_pcie_init(env);
>      /* All PCI irqs are connected to the same UIC pin (cf. UBoot source) */
>      dev = sysbus_create_simple("ppc440-pcix-host", 0xc0ec00000, uic[1][0]);
> -    pci_bus = (PCIBus *)qdev_get_child_bus(dev, "pci.0");
> -    if (!pci_bus) {
> -        error_report("couldn't create PCI controller!");
> -        exit(1);
> -    }
> +    pci_bus = PCI_BUS(qdev_get_child_bus(dev, "pci.0"));
> +

But PCI_BUS() is being passed qdev_get_child_bus(dev, "pci.0"), not
dev... so the real question here is whether this can return NULL
or not. And if this happens, is this a (1) user or (2) programming
error ?

If (1) then the "if (!pci_bus) { }" should be kept. If (2) then
it should be converted to an assert().

>      memory_region_init_alias(isa, NULL, "isa_mmio", get_system_io(),
>                               0, 0x10000);
>      memory_region_add_subregion(get_system_memory(), 0xc08000000, isa);