Re: In "pci_fixup_video" check if this is or should be the primaryvideo d

Re: In "pci_fixup_video" check if this is or should be the primaryvideo d

[Bjorn Helgaas]

On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
> June 9, 2003 Chapter 12. VGA Support".

And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
pages long.  Is there something there that prohibits two VGA devices
on the same bus?  I'm not a qemu developer, but if I were, I would
need a better hint about what is wrong before I could fix it.

Again, sorry if you said this already and I missed it.

>>[+cc Michael, Jesse, David, qemu-devel]
>>
>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
>>> I suggest you should not break the PCI specification, as a developer of proprietary
>>> hypervisor, but I think your patch is no problem.
>>> Your PCI structure is specialized structure for your virtual machine.
>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
>>> because of breaking the PCI specification.
>>
>>I assume you think qemu is breaking the PCI spec.  What exactly do you
>>think is broken?  Please give specific references to the spec.  This
>>conversation is pretty fragmented, and I came in late, so I apologize
>>if I missed this.
>>
>>Bjorn
>>

Re: Re[2]: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Bjorn Helgaas]

On Fri, Jan 17, 2014 at 3:43 AM,  <eiichiro.oiwa.nm@hitachi.com> wrote:

To make progress here, I think you'll have to be even more detailed.

> Because legacy VGA is only one device on x86 System,

Where is it documented that there can be only one legacy VGA device in
an x86 system?  I assume there exists a system with two slots on bus
0.  What happens if a user installs two VGA cards in those slots?
Does that prevent the system from working at all because it's an
illegal configuration?

I think such a system could work correctly if the I/O Space and Memory
Space bits in the command registers were only set on one of the VGA
devices.

> I think qemu has to emulate a bridge
> for legacy VGA.

My Lenovo T410 has "00:02.0 VGA compatible controller," which I assume
would qualify as a "legacy VGA device," and there's no bridge related
to it.

> The VGA Enable bit on its bridge control register has to set to 1. The VGA
> Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards
> on the same system, I think its system needs two bridges for each device.

I think you meant to say that if there are two VGA cards, we need
*one* bridge for each device, e.g., two bridges and two VGA cards.
But where does the requirement for the bridges come from?

> These bridges
> need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
> to 1. Another VGA Enable bit for second VGA has to set to 0.

If you have a set of peer bridges, i.e., bridges on the same primary
bus, I agree that at most one of them should have VGA Enable set.  If
more than one had VGA Enable set, a read on the primary bus could
receive multiple responses, which would be a PCI protocol violation.

Similarly, if there are multiple VGA devices on the same bus, I
believe that at most one could have I/O Space and Memory Space enabled
in their command registers.

But I don't see the requirement for a bridge for every VGA device.

>>On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
>>> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
>>> June 9, 2003 Chapter 12. VGA Support".
>>
>>And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
>>pages long.  Is there something there that prohibits two VGA devices
>>on the same bus?  I'm not a qemu developer, but if I were, I would
>>need a better hint about what is wrong before I could fix it.
>>
>>Again, sorry if you said this already and I missed it.
>>
>>>>[+cc Michael, Jesse, David, qemu-devel]
>>>>
>>>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
>>>>> I suggest you should not break the PCI specification, as a developer of proprietary
>>>>> hypervisor, but I think your patch is no problem.
>>>>> Your PCI structure is specialized structure for your virtual machine.
>>>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
>>>>> because of breaking the PCI specification.
>>>>
>>>>I assume you think qemu is breaking the PCI spec.  What exactly do you
>>>>think is broken?  Please give specific references to the spec.  This
>>>>conversation is pretty fragmented, and I came in late, so I apologize
>>>>if I missed this.
>>>>
>>>>Bjorn
>>>>
>>

Re: Re[2]: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Bjorn Helgaas]

By the way, your emails are not being forwarded to the mailing lists,
probably because they contain MIME or something else considered "fancy" by
the mailing list manager.  So people reading this conversation via the list
never see your emails.

There are some hints here:
  http://vger.kernel.org/majordomo-info.html
  https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches#n228
  https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/email-clients.txt

Re: Re[2]: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Michael S. Tsirkin]

On Fri, Jan 17, 2014 at 08:39:45AM -0700, Bjorn Helgaas wrote:
> On Fri, Jan 17, 2014 at 3:43 AM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> 
> To make progress here, I think you'll have to be even more detailed.

sorry, could you restate what the problem is please?

It all started with Sander trying to have two
video cards on his VM.
I suggested several solutions.
See 20140115190315.GA6661@redhat.com

Is there any other problematic configuration that's
not addressed by any of the suggested solutions?

> > Because legacy VGA is only one device on x86 System,
> 
> Where is it documented that there can be only one legacy VGA device in
> an x86 system?  I assume there exists a system with two slots on bus
> 0.  What happens if a user installs two VGA cards in those slots?
> Does that prevent the system from working at all because it's an
> illegal configuration?
> 
> I think such a system could work correctly if the I/O Space and Memory
> Space bits in the command registers were only set on one of the VGA
> devices.

Yes.
If you like, this is a bios bug - it enabled both devices.
But the disabled device would be completely non functional -
one wonders why have it in the first place.
So the cure's worse than the illness - at the moment
things actually kind of work because only one of
the devices actually claims the VGA addresses.

> > I think qemu has to emulate a bridge
> > for legacy VGA.
> 
> My Lenovo T410 has "00:02.0 VGA compatible controller," which I assume
> would qualify as a "legacy VGA device," and there's no bridge related
> to it.

If it says (prog-if 00 [VGA controller]) then it is.


> > The VGA Enable bit on its bridge control register has to set to 1. The VGA
> > Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards
> > on the same system, I think its system needs two bridges for each device.
> 
> I think you meant to say that if there are two VGA cards, we need
> *one* bridge for each device, e.g., two bridges and two VGA cards.

No, it's enough to have one device behind a bridge
with disabled VGA forwarding.

> But where does the requirement for the bridges come from?

The bridge is just a way to filter out VGA addresses
without disabling memory and IO on the device.
PCI spec could include a device independent flag to
disable VGA on the device, but it does not have that.

> > These bridges
> > need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
> > to 1. Another VGA Enable bit for second VGA has to set to 0.
> 
> If you have a set of peer bridges, i.e., bridges on the same primary
> bus, I agree that at most one of them should have VGA Enable set.  If
> more than one had VGA Enable set, a read on the primary bus could
> receive multiple responses, which would be a PCI protocol violation.
> 
> Similarly, if there are multiple VGA devices on the same bus, I
> believe that at most one could have I/O Space and Memory Space enabled
> in their command registers.
> 
> But I don't see the requirement for a bridge for every VGA device.

No, as long as you don't need all of them to work.

> >>On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> >>> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
> >>> June 9, 2003 Chapter 12. VGA Support".
> >>
> >>And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
> >>pages long.  Is there something there that prohibits two VGA devices
> >>on the same bus?  I'm not a qemu developer, but if I were, I would
> >>need a better hint about what is wrong before I could fix it.
> >>
> >>Again, sorry if you said this already and I missed it.
> >>
> >>>>[+cc Michael, Jesse, David, qemu-devel]
> >>>>
> >>>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> >>>>> I suggest you should not break the PCI specification, as a developer of proprietary
> >>>>> hypervisor, but I think your patch is no problem.
> >>>>> Your PCI structure is specialized structure for your virtual machine.
> >>>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
> >>>>> because of breaking the PCI specification.
> >>>>
> >>>>I assume you think qemu is breaking the PCI spec.  What exactly do you
> >>>>think is broken?  Please give specific references to the spec.  This
> >>>>conversation is pretty fragmented, and I came in late, so I apologize
> >>>>if I missed this.
> >>>>
> >>>>Bjorn
> >>>>
> >>

Re: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Michael S. Tsirkin]

On Fri, Jan 17, 2014 at 07:43:30PM +0900, eiichiro.oiwa.nm@hitachi.com wrote:
> Because legacy VGA is only one device on x86 System, I think qemu has to emulate a bridge
> for legacy VGA. The VGA Enable bit on its bridge control register has to set to 1. The VGA
> Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards 
> on the same system, I think its system needs two bridges for each device. These bridges
> need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
> to 1. Another VGA Enable bit for second VGA has to set to 0.
> 
> 
> >On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> >> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
> >> June 9, 2003 Chapter 12. VGA Support".
> >
> >And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
> >pages long.  Is there something there that prohibits two VGA devices
> >on the same bus?  I'm not a qemu developer, but if I were, I would
> >need a better hint about what is wrong before I could fix it.
> >
> >Again, sorry if you said this already and I missed it.
> >
> >>>[+cc Michael, Jesse, David, qemu-devel]
> >>>
> >>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> >>>> I suggest you should not break the PCI specification, as a developer of proprietary
> >>>> hypervisor, but I think your patch is no problem.
> >>>> Your PCI structure is specialized structure for your virtual machine.
> >>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
> >>>> because of breaking the PCI specification.
> >>>
> >>>I assume you think qemu is breaking the PCI spec.  What exactly do you
> >>>think is broken?  Please give specific references to the spec.  This
> >>>conversation is pretty fragmented, and I came in late, so I apologize
> >>>if I missed this.
> >>>
> >>>Bjorn
> >>>
> >

None of the bridges included in QEMU implements VGA support.
The spec explicitly says its optional, so that's ok.

As a result, you need to put device which has to work in
VGA mode on the root bus, any device behind a bridge
won't work in VGA mode (but might work in non VGA mode).

-- 
MST

Re: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Alex Williamson]

On Sun, 2014-01-19 at 12:44 +0200, Michael S. Tsirkin wrote:
> On Fri, Jan 17, 2014 at 07:43:30PM +0900, eiichiro.oiwa.nm@hitachi.com wrote:
> > Because legacy VGA is only one device on x86 System, I think qemu has to emulate a bridge
> > for legacy VGA. The VGA Enable bit on its bridge control register has to set to 1. The VGA
> > Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards 
> > on the same system, I think its system needs two bridges for each device. These bridges
> > need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
> > to 1. Another VGA Enable bit for second VGA has to set to 0.
> > 
> > 
> > >On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> > >> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
> > >> June 9, 2003 Chapter 12. VGA Support".
> > >
> > >And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
> > >pages long.  Is there something there that prohibits two VGA devices
> > >on the same bus?  I'm not a qemu developer, but if I were, I would
> > >need a better hint about what is wrong before I could fix it.
> > >
> > >Again, sorry if you said this already and I missed it.
> > >
> > >>>[+cc Michael, Jesse, David, qemu-devel]
> > >>>
> > >>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> > >>>> I suggest you should not break the PCI specification, as a developer of proprietary
> > >>>> hypervisor, but I think your patch is no problem.
> > >>>> Your PCI structure is specialized structure for your virtual machine.
> > >>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
> > >>>> because of breaking the PCI specification.
> > >>>
> > >>>I assume you think qemu is breaking the PCI spec.  What exactly do you
> > >>>think is broken?  Please give specific references to the spec.  This
> > >>>conversation is pretty fragmented, and I came in late, so I apologize
> > >>>if I missed this.
> > >>>
> > >>>Bjorn
> > >>>
> > >
> 
> None of the bridges included in QEMU implements VGA support.
> The spec explicitly says its optional, so that's ok.
> 
> As a result, you need to put device which has to work in
> VGA mode on the root bus, any device behind a bridge
> won't work in VGA mode (but might work in non VGA mode).

The ioh3420 root ports support VGA, so a q35 model is an option for
multiple VGA devices.

Re: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Michael S. Tsirkin]

On Sun, Jan 19, 2014 at 07:04:29AM -0700, Alex Williamson wrote:
> On Sun, 2014-01-19 at 12:44 +0200, Michael S. Tsirkin wrote:
> > On Fri, Jan 17, 2014 at 07:43:30PM +0900, eiichiro.oiwa.nm@hitachi.com wrote:
> > > Because legacy VGA is only one device on x86 System, I think qemu has to emulate a bridge
> > > for legacy VGA. The VGA Enable bit on its bridge control register has to set to 1. The VGA
> > > Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards 
> > > on the same system, I think its system needs two bridges for each device. These bridges
> > > need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
> > > to 1. Another VGA Enable bit for second VGA has to set to 0.
> > > 
> > > 
> > > >On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> > > >> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
> > > >> June 9, 2003 Chapter 12. VGA Support".
> > > >
> > > >And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
> > > >pages long.  Is there something there that prohibits two VGA devices
> > > >on the same bus?  I'm not a qemu developer, but if I were, I would
> > > >need a better hint about what is wrong before I could fix it.
> > > >
> > > >Again, sorry if you said this already and I missed it.
> > > >
> > > >>>[+cc Michael, Jesse, David, qemu-devel]
> > > >>>
> > > >>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> > > >>>> I suggest you should not break the PCI specification, as a developer of proprietary
> > > >>>> hypervisor, but I think your patch is no problem.
> > > >>>> Your PCI structure is specialized structure for your virtual machine.
> > > >>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
> > > >>>> because of breaking the PCI specification.
> > > >>>
> > > >>>I assume you think qemu is breaking the PCI spec.  What exactly do you
> > > >>>think is broken?  Please give specific references to the spec.  This
> > > >>>conversation is pretty fragmented, and I came in late, so I apologize
> > > >>>if I missed this.
> > > >>>
> > > >>>Bjorn
> > > >>>
> > > >
> > 
> > None of the bridges included in QEMU implements VGA support.
> > The spec explicitly says its optional, so that's ok.
> > 
> > As a result, you need to put device which has to work in
> > VGA mode on the root bus, any device behind a bridge
> > won't work in VGA mode (but might work in non VGA mode).
> 
> The ioh3420 root ports support VGA, so a q35 model is an option for
> multiple VGA devices.

Hmm, you are right, I forgot you implemented this in March.
In fact, I see that you updated bridges to support VGA
so if user wants to put both devices behind bridges,
that's also possible.

-- 
MST

Re: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Sander Eikelenboom]

Sunday, January 19, 2014, 4:09:26 PM, you wrote:

> On Sun, Jan 19, 2014 at 07:04:29AM -0700, Alex Williamson wrote:
>> On Sun, 2014-01-19 at 12:44 +0200, Michael S. Tsirkin wrote:
>> > On Fri, Jan 17, 2014 at 07:43:30PM +0900, eiichiro.oiwa.nm@hitachi.com wrote:
>> > > Because legacy VGA is only one device on x86 System, I think qemu has to emulate a bridge
>> > > for legacy VGA. The VGA Enable bit on its bridge control register has to set to 1. The VGA
>> > > Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards 
>> > > on the same system, I think its system needs two bridges for each device. These bridges
>> > > need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
>> > > to 1. Another VGA Enable bit for second VGA has to set to 0.
>> > > 
>> > > 
>> > > >On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
>> > > >> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
>> > > >> June 9, 2003 Chapter 12. VGA Support".
>> > > >
>> > > >And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
>> > > >pages long.  Is there something there that prohibits two VGA devices
>> > > >on the same bus?  I'm not a qemu developer, but if I were, I would
>> > > >need a better hint about what is wrong before I could fix it.
>> > > >
>> > > >Again, sorry if you said this already and I missed it.
>> > > >
>> > > >>>[+cc Michael, Jesse, David, qemu-devel]
>> > > >>>
>> > > >>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
>> > > >>>> I suggest you should not break the PCI specification, as a developer of proprietary
>> > > >>>> hypervisor, but I think your patch is no problem.
>> > > >>>> Your PCI structure is specialized structure for your virtual machine.
>> > > >>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
>> > > >>>> because of breaking the PCI specification.
>> > > >>>
>> > > >>>I assume you think qemu is breaking the PCI spec.  What exactly do you
>> > > >>>think is broken?  Please give specific references to the spec.  This
>> > > >>>conversation is pretty fragmented, and I came in late, so I apologize
>> > > >>>if I missed this.
>> > > >>>
>> > > >>>Bjorn
>> > > >>>
>> > > >
>> > 
>> > None of the bridges included in QEMU implements VGA support.
>> > The spec explicitly says its optional, so that's ok.
>> > 
>> > As a result, you need to put device which has to work in
>> > VGA mode on the root bus, any device behind a bridge
>> > won't work in VGA mode (but might work in non VGA mode).
>> 
>> The ioh3420 root ports support VGA, so a q35 model is an option for
>> multiple VGA devices.

> Hmm, you are right, I forgot you implemented this in March.
> In fact, I see that you updated bridges to support VGA
> so if user wants to put both devices behind bridges,
> that's also possible.


Unfortunately Xen seems to be old "pc" for the moment and the passthrough
implementation doesn't seem to have the support for defining and using bridges either.
With my limited c coding skills i also can't find how in hw/xen_pt.c it actually inits a
pci device in Qemu.

Although I still find it strange that the pci_video_fixup is ignoring the decisions that the
vga arbitration code has already made .. (make the device with the vgacon be the
primary card unless arch code overrides), for the moment i will keep my patch in my private patch queue then :-)

Re: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Michael S. Tsirkin]

On Sun, Jan 19, 2014 at 04:14:38PM +0100, Sander Eikelenboom wrote:
> 
> Sunday, January 19, 2014, 4:09:26 PM, you wrote:
> 
> > On Sun, Jan 19, 2014 at 07:04:29AM -0700, Alex Williamson wrote:
> >> On Sun, 2014-01-19 at 12:44 +0200, Michael S. Tsirkin wrote:
> >> > On Fri, Jan 17, 2014 at 07:43:30PM +0900, eiichiro.oiwa.nm@hitachi.com wrote:
> >> > > Because legacy VGA is only one device on x86 System, I think qemu has to emulate a bridge
> >> > > for legacy VGA. The VGA Enable bit on its bridge control register has to set to 1. The VGA
> >> > > Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards 
> >> > > on the same system, I think its system needs two bridges for each device. These bridges
> >> > > need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
> >> > > to 1. Another VGA Enable bit for second VGA has to set to 0.
> >> > > 
> >> > > 
> >> > > >On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> >> > > >> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
> >> > > >> June 9, 2003 Chapter 12. VGA Support".
> >> > > >
> >> > > >And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
> >> > > >pages long.  Is there something there that prohibits two VGA devices
> >> > > >on the same bus?  I'm not a qemu developer, but if I were, I would
> >> > > >need a better hint about what is wrong before I could fix it.
> >> > > >
> >> > > >Again, sorry if you said this already and I missed it.
> >> > > >
> >> > > >>>[+cc Michael, Jesse, David, qemu-devel]
> >> > > >>>
> >> > > >>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
> >> > > >>>> I suggest you should not break the PCI specification, as a developer of proprietary
> >> > > >>>> hypervisor, but I think your patch is no problem.
> >> > > >>>> Your PCI structure is specialized structure for your virtual machine.
> >> > > >>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
> >> > > >>>> because of breaking the PCI specification.
> >> > > >>>
> >> > > >>>I assume you think qemu is breaking the PCI spec.  What exactly do you
> >> > > >>>think is broken?  Please give specific references to the spec.  This
> >> > > >>>conversation is pretty fragmented, and I came in late, so I apologize
> >> > > >>>if I missed this.
> >> > > >>>
> >> > > >>>Bjorn
> >> > > >>>
> >> > > >
> >> > 
> >> > None of the bridges included in QEMU implements VGA support.
> >> > The spec explicitly says its optional, so that's ok.
> >> > 
> >> > As a result, you need to put device which has to work in
> >> > VGA mode on the root bus, any device behind a bridge
> >> > won't work in VGA mode (but might work in non VGA mode).
> >> 
> >> The ioh3420 root ports support VGA, so a q35 model is an option for
> >> multiple VGA devices.
> 
> > Hmm, you are right, I forgot you implemented this in March.
> > In fact, I see that you updated bridges to support VGA
> > so if user wants to put both devices behind bridges,
> > that's also possible.
> 
> 
> Unfortunately Xen seems to be old "pc" for the moment and the passthrough
> implementation doesn't seem to have the support for defining and using bridges either.

What do you base this claim on?
Did you actually try?
Bridges work fine for pc too.
See this for how to create a bridge and put a device behind it:
http://lists.gnu.org/archive/html/qemu-devel/2012-02/msg02765.html
this should work for all pci devices.

> With my limited c coding skills i also can't find how in hw/xen_pt.c it actually inits a
> pci device in Qemu.

hw/xen_pt.c means you use an old Qemu.
It's now in hw/xen/xen_pt.c
This is the relevant code:
    type_register_static(&xen_pci_passthrough_info);
As you can see parent is TYPE_PCI_DEVICE
which will make xen-pci-passthrough a pci device.


> Although I still find it strange that the pci_video_fixup is ignoring the decisions that the
> vga arbitration code has already made .. (make the device with the vgacon be the
> primary card unless arch code overrides), for the moment i will keep my patch in my private patch queue then :-)

Re: In "pci_fixup_video" check if this is or should be theprimaryvideo d

[Sander Eikelenboom]

Sunday, January 19, 2014, 7:27:30 PM, you wrote:

> On Sun, Jan 19, 2014 at 04:14:38PM +0100, Sander Eikelenboom wrote:
>> 
>> Sunday, January 19, 2014, 4:09:26 PM, you wrote:
>> 
>> > On Sun, Jan 19, 2014 at 07:04:29AM -0700, Alex Williamson wrote:
>> >> On Sun, 2014-01-19 at 12:44 +0200, Michael S. Tsirkin wrote:
>> >> > On Fri, Jan 17, 2014 at 07:43:30PM +0900, eiichiro.oiwa.nm@hitachi.com wrote:
>> >> > > Because legacy VGA is only one device on x86 System, I think qemu has to emulate a bridge
>> >> > > for legacy VGA. The VGA Enable bit on its bridge control register has to set to 1. The VGA
>> >> > > Enable bit describes in Table 3-10 Bridge Control register. When there are two VGA cards 
>> >> > > on the same system, I think its system needs two bridges for each device. These bridges
>> >> > > need bridge control registers. One VGA Enable bit on its bridge for legacy VGA has to set
>> >> > > to 1. Another VGA Enable bit for second VGA has to set to 0.
>> >> > > 
>> >> > > 
>> >> > > >On Thu, Jan 16, 2014 at 7:16 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
>> >> > > >> I think qemu is breaking "PCI-to-PCI Bridge Architecture Specification Revison 1.2
>> >> > > >> June 9, 2003 Chapter 12. VGA Support".
>> >> > > >
>> >> > > >And what exactly do you think qemu is doing wrong?  Chapter 12 is ten
>> >> > > >pages long.  Is there something there that prohibits two VGA devices
>> >> > > >on the same bus?  I'm not a qemu developer, but if I were, I would
>> >> > > >need a better hint about what is wrong before I could fix it.
>> >> > > >
>> >> > > >Again, sorry if you said this already and I missed it.
>> >> > > >
>> >> > > >>>[+cc Michael, Jesse, David, qemu-devel]
>> >> > > >>>
>> >> > > >>>On Wed, Jan 15, 2014 at 8:58 PM,  <eiichiro.oiwa.nm@hitachi.com> wrote:
>> >> > > >>>> I suggest you should not break the PCI specification, as a developer of proprietary
>> >> > > >>>> hypervisor, but I think your patch is no problem.
>> >> > > >>>> Your PCI structure is specialized structure for your virtual machine.
>> >> > > >>>> Maybe, your virtual machine will be causing another problem on Linux or other kernels
>> >> > > >>>> because of breaking the PCI specification.
>> >> > > >>>
>> >> > > >>>I assume you think qemu is breaking the PCI spec.  What exactly do you
>> >> > > >>>think is broken?  Please give specific references to the spec.  This
>> >> > > >>>conversation is pretty fragmented, and I came in late, so I apologize
>> >> > > >>>if I missed this.
>> >> > > >>>
>> >> > > >>>Bjorn
>> >> > > >>>
>> >> > > >
>> >> > 
>> >> > None of the bridges included in QEMU implements VGA support.
>> >> > The spec explicitly says its optional, so that's ok.
>> >> > 
>> >> > As a result, you need to put device which has to work in
>> >> > VGA mode on the root bus, any device behind a bridge
>> >> > won't work in VGA mode (but might work in non VGA mode).
>> >> 
>> >> The ioh3420 root ports support VGA, so a q35 model is an option for
>> >> multiple VGA devices.
>> 
>> > Hmm, you are right, I forgot you implemented this in March.
>> > In fact, I see that you updated bridges to support VGA
>> > so if user wants to put both devices behind bridges,
>> > that's also possible.
>> 
>> 
>> Unfortunately Xen seems to be old "pc" for the moment and the passthrough
>> implementation doesn't seem to have the support for defining and using bridges either.

> What do you base this claim on?
> Did you actually try?
> Bridges work fine for pc too.
> See this for how to create a bridge and put a device behind it:
> http://lists.gnu.org/archive/html/qemu-devel/2012-02/msg02765.html
> this should work for all pci devices.

I was saying Xen (and it's toolstack incombination with it's specific xen pci passthrough implementation), not Qemu ..
Creating a bridge is not that difficult as you can easily let xen add things to the commandline that's being
generated to start Qemu. Changing things is more difficult and the pci passthrough stuff is going with QMP anyway.


>> With my limited c coding skills i also can't find how in hw/xen_pt.c it actually inits a
>> pci device in Qemu.

> hw/xen_pt.c means you use an old Qemu.
> It's now in hw/xen/xen_pt.c
> This is the relevant code:
>     type_register_static(&xen_pci_passthrough_info);
> As you can see parent is TYPE_PCI_DEVICE
> which will make xen-pci-passthrough a pci device.

A sorry no i'm using Qemu pulled from the Qemu git tree .. just typed that path from memory ..

Ok thx for the pointer, hope i can find how to add it to a specific bridge instead of the root bus.

>> Although I still find it strange that the pci_video_fixup is ignoring the decisions that the
>> vga arbitration code has already made .. (make the device with the vgacon be the
>> primary card unless arch code overrides), for the moment i will keep my patch in my private patch queue then :-)