Re: [Qemu-devel] [PATCH] vga: make stdvga the global default

[Eduardo Habkost <ehabkost@redhat.com>]

On Wed, Jul 04, 2018 at 01:28:59PM +0200, Gerd Hoffmann wrote:
> This reverts the stdvga vs. cirrus selection logic.  Current state is
> that "cirrus" is the default and MachineClass->default_display is set to
> "std" by some machine types to override that.
> 
> The patch makes "std" the default.  Setting default_display to "std" is
> dropped.  Machine types which likely depend on cirrus (alpha, mips, old
> pc versions) will explicitly set default_display to "cirrus".
> 
> With this patch applied all ppc machine types will use "std" as default
> display, no matter whenever cirrus-vga is compiled in or not.
> 
> Fixes: 29f9cef39e ppc: Include vga cirrus card into the compiling process
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

So, the current state is that default_display==NULL is
unpredictable and fragile.  The last hunk in this patch changes
the default when default_dispay==NULL, but it's still fragile.

I don't think we must audit all machine-types with
default_display=NULL today.  But:

[...]
> diff --git a/hw/alpha/dp264.c b/hw/alpha/dp264.c
> index 80b987f7fb..668e6d099f 100644
> --- a/hw/alpha/dp264.c
> +++ b/hw/alpha/dp264.c
> @@ -182,6 +182,7 @@ static void clipper_machine_init(MachineClass *mc)
>      mc->max_cpus = 4;
>      mc->is_default = 1;
>      mc->default_cpu_type = ALPHA_CPU_TYPE_NAME("ev67");
> +    mc->default_display = "cirrus";

OK.

>  }
>  
>  DEFINE_MACHINE("clipper", clipper_machine_init)
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index dc09466b3e..30ad22e2e3 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -424,7 +424,6 @@ static void pc_i440fx_machine_options(MachineClass *m)
>      m->family = "pc_piix";
>      m->desc = "Standard PC (i440FX + PIIX, 1996)";
>      m->default_machine_opts = "firmware=bios-256k.bin";
> -    m->default_display = "std";
>      machine_class_allow_dynamic_sysbus_dev(m, TYPE_RAMFB_DEVICE);

I wouldn't like to do this.  Long term, it would be a good idea
to have zero machines with default_display==NULL, so let's keep
default_machine="std" on PC?


>  }
>  
> @@ -566,7 +565,7 @@ static void pc_i440fx_2_1_machine_options(MachineClass *m)
>      PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
>      pc_i440fx_2_2_machine_options(m);
>      m->hw_version = "2.1.0";
> -    m->default_display = NULL;
> +    m->default_display = "cirrus";

OK.

>      SET_MACHINE_COMPAT(m, PC_COMPAT_2_1);
>      pcmc->smbios_uuid_encoded = false;
>      pcmc->enforce_aligned_dimm = false;
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index 532241e3f8..8f2c8c8b8b 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -303,7 +303,6 @@ static void pc_q35_machine_options(MachineClass *m)
>      m->desc = "Standard PC (Q35 + ICH9, 2009)";
>      m->units_per_default_bus = 1;
>      m->default_machine_opts = "firmware=bios-256k.bin";
> -    m->default_display = "std";

Same comment as pc_i440fx_machine_options() above.

>      m->no_floppy = 1;
>      machine_class_allow_dynamic_sysbus_dev(m, TYPE_AMD_IOMMU_DEVICE);
>      machine_class_allow_dynamic_sysbus_dev(m, TYPE_INTEL_IOMMU_DEVICE);
> diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
> index 3467451482..998971c53a 100644
> --- a/hw/mips/mips_malta.c
> +++ b/hw/mips/mips_malta.c
> @@ -1242,6 +1242,7 @@ static void mips_malta_machine_init(MachineClass *mc)
>      mc->block_default_type = IF_IDE;
>      mc->max_cpus = 16;
>      mc->is_default = 1;
> +    mc->default_display = "cirrus";

OK.

>  #ifdef TARGET_MIPS64
>      mc->default_cpu_type = MIPS_CPU_TYPE_NAME("20Kc");
>  #else
> diff --git a/hw/mips/mips_r4k.c b/hw/mips/mips_r4k.c
> index d5725d0555..c4c7ee8aa5 100644
> --- a/hw/mips/mips_r4k.c
> +++ b/hw/mips/mips_r4k.c
> @@ -295,6 +295,7 @@ static void mips_machine_init(MachineClass *mc)
>      mc->desc = "mips r4k platform";
>      mc->init = mips_r4k_init;
>      mc->block_default_type = IF_IDE;
> +    mc->default_display = "cirrus";

OK.

>  #ifdef TARGET_MIPS64
>      mc->default_cpu_type = MIPS_CPU_TYPE_NAME("R4000");
>  #else
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 3f5e1d3ec2..0ab90f3aa8 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3962,7 +3962,6 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
>      mc->no_parallel = 1;
>      mc->default_boot_order = "";
>      mc->default_ram_size = 512 * MiB;
> -    mc->default_display = "std";

Same comment as pc_i440fx_machine_options() above.

>      mc->kvm_type = spapr_kvm_type;
>      machine_class_allow_dynamic_sysbus_dev(mc, TYPE_SPAPR_PCI_HOST_BRIDGE);
>      mc->pci_allow_0_address = true;
> diff --git a/vl.c b/vl.c
> index 16b913f9d5..e60bf2d6cd 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -4475,10 +4475,10 @@ int main(int argc, char **argv, char **envp)
>      if (default_vga) {
>          if (machine_class->default_display) {
>              vga_model = machine_class->default_display;
> -        } else if (vga_interface_available(VGA_CIRRUS)) {
> -            vga_model = "cirrus";
>          } else if (vga_interface_available(VGA_STD)) {
>              vga_model = "std";
> +        } else if (vga_interface_available(VGA_CIRRUS)) {
> +            vga_model = "cirrus";

If we don't make the machines above have default_display=NULL, we
won't need this hunk, right?  In either case, I suggest doing
this change on a separate patch.

-- 
Eduardo