mips-fulong2e: obey -vga none

[Qemu-devel] [PATCH] mips-fulong2e: obey -vga none

Posted by Paolo Bonzini 5 years, 1 month ago

Do not create an ATI VGA if "-vga none" was passed on the command line.

Cc: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/mips/mips_fulong2e.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/hw/mips/mips_fulong2e.c b/hw/mips/mips_fulong2e.c
index 9d7480ed31..05a5a823a1 100644
--- a/hw/mips/mips_fulong2e.c
+++ b/hw/mips/mips_fulong2e.c
@@ -349,10 +349,12 @@ static void mips_fulong2e_init(MachineState *machine)
                                &smbus, &isa_bus);
 
     /* GPU */
-    dev = DEVICE(pci_create(pci_bus, -1, "ati-vga"));
-    qdev_prop_set_uint32(dev, "vgamem_mb", 16);
-    qdev_prop_set_uint16(dev, "x-device-id", 0x5159);
-    qdev_init_nofail(dev);
+    if (vga_interface_type != VGA_NONE) {
+        dev = DEVICE(pci_create(pci_bus, -1, "ati-vga"));
+        qdev_prop_set_uint32(dev, "vgamem_mb", 16);
+        qdev_prop_set_uint16(dev, "x-device-id", 0x5159);
+        qdev_init_nofail(dev);
+    }
 
     /* Populate SPD eeprom data */
     spd_data = spd_data_generate(DDR, ram_size, &err);
-- 
2.20.1

Re: [Qemu-devel] [PATCH] mips-fulong2e: obey -vga none

Posted by Aleksandar Markovic 5 years, 1 month ago

> From: Paolo Bonzini <pbonzini@redhat.com>
> Cc: philmd@redhat.com; BALATON Zoltan; Aleksandar Markovic; Aleksandar Rikalo; Aurelien Jarno
> Subject: [PATCH] mips-fulong2e: obey -vga none
> 
> Do not create an ATI VGA if "-vga none" was passed on the command line.
> 
> Cc: BALATON Zoltan <balaton@eik.bme.hu>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

This looks like a very good point to me.

I am going to wait for comments of others.

Many thanks, Paolo!
Aleksandar

P.S. Balaton Zoltan, what is your first, and what is your last name? I know "Zoltan" can be both.

>  hw/mips/mips_fulong2e.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/mips/mips_fulong2e.c b/hw/mips/mips_fulong2e.c
> index 9d7480ed31..05a5a823a1 100644
> --- a/hw/mips/mips_fulong2e.c
> +++ b/hw/mips/mips_fulong2e.c
> @@ -349,10 +349,12 @@ static void mips_fulong2e_init(MachineState *machine)
>                                 &smbus, &isa_bus);
> 
>      /* GPU */
> -    dev = DEVICE(pci_create(pci_bus, -1, "ati-vga"));
> -    qdev_prop_set_uint32(dev, "vgamem_mb", 16);
> -    qdev_prop_set_uint16(dev, "x-device-id", 0x5159);
> -    qdev_init_nofail(dev);
> +    if (vga_interface_type != VGA_NONE) {
> +        dev = DEVICE(pci_create(pci_bus, -1, "ati-vga"));
> +        qdev_prop_set_uint32(dev, "vgamem_mb", 16);
> +        qdev_prop_set_uint16(dev, "x-device-id", 0x5159);
> +        qdev_init_nofail(dev);
> +    }
> 
>      /* Populate SPD eeprom data */
>      spd_data = spd_data_generate(DDR, ram_size, &err);
> --
> 2.20.1
>

Re: [Qemu-devel] [PATCH] mips-fulong2e: obey -vga none

Posted by BALATON Zoltan 5 years, 1 month ago

On Tue, 19 Mar 2019, Paolo Bonzini wrote:
> Do not create an ATI VGA if "-vga none" was passed on the command line.
>
> Cc: BALATON Zoltan <balaton@eik.bme.hu>

Thanks, I did not know about this variable. Although the real hardware has 
the GPU soldered on the mainboard it makes sense to allow it to be 
disabled in QEMU especially at this stage when Linux kernel has some 
problem with it so this is a good idea.

Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>

When changing it you could also replace the -1 in pci_create with 
PCI_DEVFN(FULONG2E_ATI_SLOT, 0) to match the address the board has or 
should that be a separate patch?

Regards,
BALATON Zoltan

> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> hw/mips/mips_fulong2e.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/hw/mips/mips_fulong2e.c b/hw/mips/mips_fulong2e.c
> index 9d7480ed31..05a5a823a1 100644
> --- a/hw/mips/mips_fulong2e.c
> +++ b/hw/mips/mips_fulong2e.c
> @@ -349,10 +349,12 @@ static void mips_fulong2e_init(MachineState *machine)
>                                &smbus, &isa_bus);
>
>     /* GPU */
> -    dev = DEVICE(pci_create(pci_bus, -1, "ati-vga"));
> -    qdev_prop_set_uint32(dev, "vgamem_mb", 16);
> -    qdev_prop_set_uint16(dev, "x-device-id", 0x5159);
> -    qdev_init_nofail(dev);
> +    if (vga_interface_type != VGA_NONE) {
> +        dev = DEVICE(pci_create(pci_bus, -1, "ati-vga"));
> +        qdev_prop_set_uint32(dev, "vgamem_mb", 16);
> +        qdev_prop_set_uint16(dev, "x-device-id", 0x5159);
> +        qdev_init_nofail(dev);
> +    }
>
>     /* Populate SPD eeprom data */
>     spd_data = spd_data_generate(DDR, ram_size, &err);
>

[Qemu-devel] What should a virtual board emulate? (was: [PATCH] mips-fulong2e: obey -vga none)

Posted by Markus Armbruster 5 years, 1 month ago

BALATON Zoltan <balaton@eik.bme.hu> writes:

> On Tue, 19 Mar 2019, Paolo Bonzini wrote:
>> Do not create an ATI VGA if "-vga none" was passed on the command line.
>>
>> Cc: BALATON Zoltan <balaton@eik.bme.hu>
>
> Thanks, I did not know about this variable. Although the real hardware
> has the GPU soldered on the mainboard it makes sense to allow it to be
> disabled in QEMU especially at this stage when Linux kernel has some
> problem with it so this is a good idea.

I'm not sure.

For better or worse, we have a whole bunch of global variables
(manipulated with command line options) our board code may elect to
honor.

When a command line option ends up in a global variable the board
doesn't honor, we sometimes warn the user his option is being ignored,
and we sometimes ignore it silently.  But that's not what I'd like to
discuss today.

My question today is what a virtual board should emulate, and what
-nodefaults should mean.

The most straightforward case is emulating a single physical board, so
that we emulate exactly what's on the board, no more, no less.  Anything
that can be plugged into the board we model as pluggable device you add
with -device.

We can still have convenience options for adding such pluggable devices
in a simpler way.

We can even plug some by default.  -nodefaults suppresses that, i.e. it
gives you exactly the physical board with nothing plugged in.

Things get a bit more interesting when we're emulating a family of
physical boards.  Say there's a bare-bones version, and another with
more goodies soldered on.  While we can model the two as distinct
machine types, modelling as a single machine type with options (machine
properties or the global variables) may be more convenient.  That's
okay.

Note that -nodefault still gives you a faithful emulation of a physical
board: the bare-bones one.

Things get more interesting still when we're emulating a somewhat fuzzy
idea of a zoo of physical boards, like x86 PC.  I think the difference
to the previous case is mostly ambiguity that comes out of the
fuzziness.

Here, -nodefault gives you an emulation of a physical board that could
plausibly exist.

Now let's circle back to this patch.  mips-fulong2e emulates a physical
board that has ATI VGA soldered on.  After this patch, -nodefaults gives
you an emulation of something that doesn't exist.  Right now, that
virtual frankenboard happens to work better than the more faithful
emulation that has the VGA, but that's just bugs.  Working around bugs
is certainly relevant, just not for guiding us on basic design issues.

Mind, I'm not demanding mips-fulong2e should continue to ignore -vga;
that's for its maintainer to decide.  I don't demand, I ask: what should
a virtual board emulate?  What should -nodefaults do?

[...]

Re: [Qemu-devel] What should a virtual board emulate? (was: [PATCH] mips-fulong2e: obey -vga none)

Posted by Philippe Mathieu-Daudé 5 years, 1 month ago

Le mer. 20 mars 2019 07:13, Markus Armbruster <armbru@redhat.com> a écrit :

> BALATON Zoltan <balaton@eik.bme.hu> writes:
>
> > On Tue, 19 Mar 2019, Paolo Bonzini wrote:
> >> Do not create an ATI VGA if "-vga none" was passed on the command line.
> >>
> >> Cc: BALATON Zoltan <balaton@eik.bme.hu>
> >
> > Thanks, I did not know about this variable. Although the real hardware
> > has the GPU soldered on the mainboard it makes sense to allow it to be
> > disabled in QEMU especially at this stage when Linux kernel has some
> > problem with it so this is a good idea.
>
> I'm not sure.
>
> For better or worse, we have a whole bunch of global variables
> (manipulated with command line options) our board code may elect to
> honor.
>
> When a command line option ends up in a global variable the board
> doesn't honor, we sometimes warn the user his option is being ignored,
> and we sometimes ignore it silently.  But that's not what I'd like to
> discuss today.
>
> My question today is what a virtual board should emulate, and what
> -nodefaults should mean.
>
> The most straightforward case is emulating a single physical board, so
> that we emulate exactly what's on the board, no more, no less.  Anything
> that can be plugged into the board we model as pluggable device you add
> with -device.
>

Yes.


> We can still have convenience options for adding such pluggable devices
> in a simpler way.
>
> We can even plug some by default.  -nodefaults suppresses that, i.e. it
> gives you exactly the physical board with nothing plugged in.


Ideally.


> Things get a bit more interesting when we're emulating a family of
> physical boards.  Say there's a bare-bones version, and another with
> more goodies soldered on.  While we can model the two as distinct
> machine types, modelling as a single machine type with options (machine
> properties or the global variables) may be more convenient.  That's
> okay.
>
> Note that -nodefault still gives you a faithful emulation of a physical
> board: the bare-bones one.
>
> Things get more interesting still when we're emulating a somewhat fuzzy
> idea of a zoo of physical boards, like x86 PC.  I think the difference
> to the previous case is mostly ambiguity that comes out of the
> fuzziness.
>
> Here, -nodefault gives you an emulation of a physical board that could
> plausibly exist.
>
> Now let's circle back to this patch.  mips-fulong2e emulates a physical
> board that has ATI VGA soldered on.  After this patch, -nodefaults gives
> you an emulation of something that doesn't exist.  Right now, that
> virtual frankenboard happens to work better than the more faithful
> emulation that has the VGA, but that's just bugs.  Working around bugs
> is certainly relevant, just not for guiding us on basic design issues.
>

-display/-vga options suffers same clarity problems than -net. Is it a card
device or a cable linking to a network? Here is it a card device or a cable
connecting a monitor display?
When cards plugged on bus via extractible slots, they are optional. If no
slot (soldered) or no bus (mmio) they aren't optional. Display monitors are
optional.


> Mind, I'm not demanding mips-fulong2e should continue to ignore -vga;
> that's for its maintainer to decide.  I don't demand, I ask: what should
> a virtual board emulate?  What should -nodefaults do?
>

IMHO -nodefaults contains soldered/mmio chipsets.
Whether you plug a display or not is a different story.


> [...]
>
>

Re: [Qemu-devel] What should a virtual board emulate? (was: [PATCH] mips-fulong2e: obey -vga none)

Posted by Paolo Bonzini 5 years, 1 month ago

On 20/03/19 11:03, Philippe Mathieu-Daudé wrote:
> 
> 
> -display/-vga options suffers same clarity problems than -net. Is it a
> card device or a cable linking to a network? Here is it a card device or
> a cable connecting a monitor display? 

-display is a cable, -vga is a card ("-nic none" is a card, "-nic
anythingelse" is a card+cable; "-net nic" is a card, "-net anythingelse"
is a cable).

>     Mind, I'm not demanding mips-fulong2e should continue to ignore -vga;
>     that's for its maintainer to decide.  I don't demand, I ask: what should
>     a virtual board emulate?  What should -nodefaults do?
> 
> IMHO -nodefaults contains soldered/mmio chipsets.
> Whether you plug a display or not is a different story.

In principle you could also cut the copper tracks that connect the card
to the PCI bus...

Paolo