On Thu, Nov 18, 2010 at 01:55:29PM +0200, Gleb Natapov wrote: > On Thu, Nov 18, 2010 at 01:33:08PM +0200, Michael S. Tsirkin wrote: > > On Thu, Nov 18, 2010 at 11:57:51AM +0200, Gleb Natapov wrote: > > > On Thu, Nov 18, 2010 at 11:30:27AM +0200, Michael S. Tsirkin wrote: > > > > On Thu, Nov 18, 2010 at 11:11:49AM +0200, Gleb Natapov wrote: > > > > > On Thu, Nov 18, 2010 at 11:03:21AM +0200, Michael S. Tsirkin wrote: > > > > > > On Thu, Nov 18, 2010 at 10:09:35AM +0200, Gleb Natapov wrote: > > > > > > > On Wed, Nov 17, 2010 at 08:00:08PM +0200, Michael S. Tsirkin > > > > > > > wrote: > > > > > > > > > >> If so: does qemu > > > > > > > > > >>emulate this correctly? > > > > > > > > > > > > > > > > > > > >It mostly does. > > > > > > > > > > > > > > > > > > I doubt it actually enables/disables the legacy vga ports. > > > > > > > > > > > > > > > > I'll check when I have the time. We can fix it if it doesn't, > > > > > > > > > > > > > > > So many guests (all of them?) just assume that vga ports and > > > > > > > framebuffer is there. > > > > > > > > > > > > Why do you think they disable io memory then? > > > > > > > > > > > Who and how and when disables io memory? > > > > > > > > I think guest will do this if you disable the device through the device > > > > manager. This might need a reboot to become effective. > > > > > > > Try to do it with primary VGA adapter and tell us what happens :) > > > > > > > > Some guests are designed to run > > > > > even on old ISA machines that have no way to disable anything. The > > > > > device is just there. > > > > > > > > > > This is the same with IDE ports. BIOS "knows" legacy ISA ports and > > > > > just > > > > > program them into PCI IO bars to be nice. > > > > > > > > HAven't checked IDE, for VGA AFAIK BIOS does not program legacy ports in > > > > the card, they are hardwired there. However, the card must not claim any > > > > io transactions if IO memory is disabled in command register. > > > > > > > Is this correct also for legacy ports? > > > > Yes. The spec is quite explicit on this point: > > > > A function that supports a PC legacy function (IDE, VGA, etc.) is > > allowed to claim those addresses associated with the specific function > > when the I/O Space (see Figure 6-2) enable bit is set. These addresses > > are not requested using a Base Address register but are assigned by > > initialization software. If a device identifies itself as a legacy > > function (class code), the initialization software grants the device > > permission to claim the I/O legacy addresses by setting the device’s I/O > > Space enable bit. > > > > > What do they mean by "initialization software".
BIOS or OS. > How addresses is > assigned by initialization software without use of Base Address register? As it says: " If a device identifies itself as a legacy " function (class code), the initialization software grants the device " permission to claim the I/O legacy addresses by setting the device’s " I/O " Space enable bit. So you look at the class code and know which addresses will be claimed. The relevant table is in the appendix D, take a look there. > Looks like "initialization software" is something internal to HW. Not really. Seabios does this simply by enabling io unconditionally. It could easily detect multiple VGA cards and only enable one. > And what spec says about legacy mmio? What do you want to know? > > > This wouldn't be backwards > > > compatible to ISA machines, so old software my not run properly back in > > > the days when transaction from ISA to PCI happened. > > > > initialization software could be the BIOS. > > So maybe BIOS update was needed in the transition. > > > That is possible. > > > > So my guess is that > > > old ISA ports works in backwards compatible way. > > > > The spec seems to contradict this. > > > > > > When qemu is started, it works correctly: the io memory is disabled and > > > > card does > > > > not claim any io. Then BIOS comes along and enables io. At this point > > > > map callback is invoked and maps io memory, card starts claiming io. > > > Looking at the code I see that cirrus claims all IO ports and > > > framebuffer memory during init function unconditionally. > > > > So that may be OK for ISA, but not for PCI. > > > The code does it for both. Yep. So it's a bug. > > > > > > > > What is broken is that if BIOS/guest then disables IO memory, > > > > (I think - even if guest is rebooted!) we will keep claiming IO > > > > transactions. > > > > That our emulation does this seems to be a clear spec violation, we are > > > > just lucky that BIOS/guest does not do this at the moment. > > > > > > > > > > > > > > > > > > > So what "fixing" this will buy us? > > > > > > > > > > > > Besides spec compliancy, you mean? Ability to support multiple VGA > > > > > > cards. That's how it works I think: BIOS enables IO on the primary > > > > > > VGA device only. > > > > > > > > > > > What spec defines hot-plug for primary VGA adapter? > > > > > > > > No idea about hotplug. I am talking about multiple VGA cards, > > > > enabling/disabling them dynamically should be possible. > > > Of course. With properly designed VGA card you should be able to have > > > more then one, > > > > And, for that to have a chance to work when all cards are identical, you > > don't claim IO when IO is disabled. > > > But then only one card will be able to use IO since enabling IO on more > the one cards will cause conflict. Sure. That's life for legacy io though. > > > but one of them will provide legacy functionality > > > and is not removable. > > > > The guest might not support hotplug. But there's no way > > it can prevent surprise removal. qemu should not crash > > when this happens. > Qemu can prevent any removal, surprise or not. Qemu can just > disallow device removal. Yes, but that won't emulate real hardware faithfully. On real hardware with a hotplug supporting slot (and without an EM lock :) ) you can yank the card out and the guest can do nothing about it. > -- > Gleb.
