On Fri, Jan 17, 2014 at 3:43 AM, <eiichiro.oiwa.nm@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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 >>>> >> -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
